Science

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NIH budget cuts affect research funding beyond US borders

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European leaders say they will fill the funding void. Is that realistic?

Credit: E+ via Getty Images

Rory de Vries, an associate professor of virology in the Netherlands, was lifting weights at the gym when he noticed a WhatsApp message from his research partners at Columbia University, telling him his research funding had been cancelled. The next day he received the official email: “Hi Rory, Columbia has received a termination notice for this contract, including all subcontracts,” it stated. “Unfortunately, we must advise you to immediately stop work and cease incurring charges on this subcontract.”

De Vries was disappointed, though not surprised—his team knew this might happen under the new Trump administration. His projects focused on immune responses and a new antiviral treatment for respiratory viruses like Covid-19. Animals had responded well in pre-clinical trials, and he was about to explore the next steps for applications in humans. But the news, which he received in March, left him with a cascade of questions: What would happen to the doctoral student he had just hired for his project, a top candidate plucked from a pool of some 300 aspiring scientists? How would his team comply with local Dutch law, which, unlike the US, forbids terminating a contract without cause or notice? And what did the future hold for his projects, two of which contained promising data for treating Covid-19 and other respiratory illnesses in humans?

It was all up in the air, leaving de Vries, who works at the Erasmus Medical Center in Rotterdam and whose research has appeared in top-tier publications scrambling for last-minute funding from the Dutch government or the European Union.

Of the 20 members in his group, he will soon run out of money to pay the salaries for four. As of June, he

estimated that his team has enough to keep going for about six months in its current form if it draws money from other funding sources.

But that still leaves funding uncertain in the long-term: “So, yeah, that’s a little bit of an emergency solution,” he said.

Cuts to science funding in the US have devastated American institutions, hitting cancer research and other vital fields, but they also affect a raft of international collaborations and scientists based abroad. In Canada, Australia, South Africa and elsewhere, projects receiving funds from the National Institutes of Health have been terminated or stalled due to recent budget cuts.

Researchers in Europe and the US have long collaborated to tackle tough scientific questions. Certain fields, like rare diseases, particularly benefit from international collaboration because it widens the pool of patients available to study. European leaders have said that they will step into the gap created by Trump’s NIH cuts to make Europe a magnet for science—and they have launched a special initiative to attract US scientists. But some researchers doubt that Europe alone can truly fill the void.

In many European countries, scientist salaries are modest and research funding has lagged behind inflation in recent years. In a May press release, a French scientists’ union described current pay as “scandalously low” and said research funding in France and Europe as a whole lags behind the US, South Korea, China, Taiwan, and Japan. Europe and its member states would need to increase research funding by up to 150 billion euros (roughly USD $173 billion) per year to properly support science, said Boris Gralak, general secretary of the French union, in an interview with Undark.

The shifts are not just about money, but the pattern of how international research unfolds, said Stefan Pfister, a pediatric cancer specialist in Germany who has also received NIH funds. The result, he said, is “this kind of capping and compromising well-established collaborations.”

Funding beyond US borders

For decades, international researchers have received a small slice of the National Institutes of Health budget. In 2024, out of an overall budget of $48 billion, the NIH dispensed $69 million to 125 projects across the European continent and $262 million in funding worldwide, according to the NIH award database.

The US and Europe “have collaborated in science for, you know, centuries at this point,” said Cole Donovan, associate director of science and technology ecosystem development at the Federation of American Scientists, noting that the relationship was formalized in 1997 in an agreement highlighting the two regions’ common interests.

And it has overall been beneficial, said Donovan, who worked in the State Department for a decade to help facilitate such collaborations. In some cases, European nations simply have capabilities that do not exist in the US, like the Czech Republic and Romania, he said, which have some of the most sophisticated laser facilities in the world.

“If you’re a researcher and you want to use those facilities,” he added, “you have to have a relationship with people in those countries.”

Certain fields, like rare diseases, particularly benefit from international collaboration because it widens the pool of patients available to study.

The shared nature of research is driven by personal connections and scientific interest, Donovan said: “The relationship in science and technology is organic.”

But with the recent cuts to NIH funding, the fate of those research projects—particularly on the health effects of climate change, transgender health, and Covid-19—has been thrown into question. On May 1, the NIH said it would not reissue foreign subawards, which fund researchers outside the US who work with American collaborators—or agree to US researchers asking to add a foreign colleague to a project. The funding structure lacked transparency and could harm national security, the NIH stated, though it noted that it would not “retroactively revise ongoing awards to remove foreign subawards at this time.” (The NIH would continue to support direct foreign awards, according to the statement.)

The cuts have hit European researchers like de Vries, whose institution, Erasmus MC, was a sub-awardee on three Columbia University grants to support his work. Two projects on Covid-19 transmission and treatment have ended abruptly, while another, on a potential treatment for measles, has been frozen, awaiting review at the end of May, though by late June he still had no news and said he assumed it would not be renewed. “We’re trying to scrape together some money to do some two or three last experiments, so we at least can publish the work and that it’s in literature and anyone else can pick it up,” he said. “But yeah, the work has stopped.”

His Ph.D. students must now shift the focus of their theses; for some, that means pivoting after nearly three years of study.

De Vries’ team has applied for funds from the Dutch government, as well as sought industry funding, for a new project evaluating a vaccine for RSV—something he wouldn’t have done otherwise, he said, since industry funding can limit research questions. “Companies might not be interested in in-depth immunological questions, or a side-by-side comparison of their vaccine with the direct competition,” he wrote in an email.

International scientists who have received direct awards have so far been unaffected, but say they are still nervous about potential further cuts. Pfister, for example, is now leading a five-year project to develop treatments for childhood tumors; with the majority of funding coming from NIH and Cancer Research U.K., a British-based cancer charity, “not knowing what the solution will look like next year,” he said, “generates uncertainties.”

The jointly funded $25 million project—which scientists from nine institutions across five countries including the US are collaborating on—explores treatments for seven childhood cancers and offers a rare opportunity to make progress in tackling tumors in children, Pfister added, as treatments have lagged in the field due to the small market and the high costs of development. Tumors in children differ from those in adults and, until recently, were harder to target, said Pfister. But new discoveries have allowed researchers to target cancer more specifically in children, and global cooperation is central to that progress.

The US groups, which specialize in drug chemistry, develop lead compounds for potential drugs. Pfister’s team then carries out experiments on toxicity and effectiveness. The researchers hope to bring at least one treatment, into early-phase clinical trials.

Funding from NIH is confirmed for this financial year. Beyond that, the researchers are staying hopeful, Pfister said.

“It’s such an important opportunity for all of us to work together,” said Pfister, “that we don’t want to think about worst-case scenarios.”

Pfister told Undark that his team in Heidelberg, Germany, has assembled the world´s biggest store of pediatric cancer models; no similar stock currently exists in the US The work of the researchers is complementary, he stressed: “If significant parts would drop out, you cannot run the project anymore.”

Rare diseases benefit from international projects, he added. In these fields, “We don’t have the patient numbers, we don’t have the critical mass,” in one country alone, he said. In his field, researchers conduct early clinical trials in patients on both sides of the Atlantic. “That’s just not because we are crazy, but just because this the only way to physically conduct them.”

The US has spearheaded much drug development, he noted. “Obviously the US has been the powerhouse for biomedical research for the last 50 years, so it’s not surprising that some of the best people and the best groups are sitting there,” he said. A smaller US presence in the field would reduce the critical mass of people and resources available, which would be a disaster for patients, he said. “Any dreams of this all moving to Europe are illusions in my mind.”

While Europe has said it will step in to fill the gap, the amounts discussed were not enough, Gralak said. The amount of money available in Europe “is a very different order of magnitude,” Pfister said. It also won’t help their colleagues in the US, who European researchers need to thrive in order to maintain necessary collaborations, he said. “In the US, we are talking about dozens of billions of dollars less in research, and this cannot be compensated by any means, by the EU or any other funder.” Meanwhile, the French scientists’ union said the country has failed to meet funding promises made as long ago as 2010.

And although Europe receives a sliver of NIH funds, these cuts could have a real impact on public health. De Vries said that his measles treatment was at such an early stage that its potential benefits remained unproven, but if effective it could have been the only treatment of its kind at a time when cases are rising.

And he said the stalling of both his work and other research on Covid-19 leaves the world less prepared for a future pandemic. The antiviral drug he has developed had positive results in ferrets but needs further refinement to work in humans. If the drugs were available for people, “that would be great,” he said. “Then we could actually work on interrupting a pandemic early.”

New opportunities for Europe

The shift in US direction offers an opportunity for the EU, said Mike Galsworthy, a British scientist who campaigned to unite British and EU science in the wake of Brexit. The US will no longer be the default for ambitious researchers from across the world, he said: “It’s not just US scientists going to Canada and Europe. There’s also going to be the huge brain diversion.” he said. “If you are not a native English speaker and not White, you might be extra nervous about going to the States for work there right now,” he added.

And in recent weeks, European governments have courted fleeing scientists. In April, France launched a platform called Choose France for Science, which allows institutions to request funding for international researchers, and highlights an interest in health, climate science, and artificial intelligence, among other research areas Weeks later, the European Union announced a new program called Choose Europe for Science, aiming to make Europe a “magnet for researchers.” It includes a 500 million Euro (roughly USD $578 million) funding package for 2025-2027, new seven-year “super grants,” to attract the best researchers, and top-up funds that would help scientists from outside Europe settle into their new institution of choice.

The initial funding comes from money already allocated to Horizon Europe—the EU’s central research and innovation funding program. But some researchers are skeptical. The French union leader, Gralak, who is also a researcher in mathematical physics, described the programs as PR initiatives. He criticized European leaders for taking advantage of the problems in US science to attract talent to Europe, and said leaders should support science in Europe through proper and sufficient investment. The programs are “derisory and unrealistic,” he said.

“It’s not just US scientists going to Canada and Europe. There’s also going to be the huge brain diversion.”

Others agreed that Europe’s investment in science is inadequate. Bringing scientists to Europe would be “great for science and the talent, but that also means that will come from a line where there’s normally funding for European researchers,” said de Vries, the researcher from Rotterdam. As Mathilde Richard, a colleague of de Vries who works on viruses and has five active NIH grants, told Undark: “Why did I start to apply to NIH funds? And still, the most straightforward answer is that there isn’t enough in Europe.”

In the Netherlands, a rightwing government has said it will cut science funding by a billion euros over the next five years. And while the flagship program Horizon Europe encourages large-scale projects spanning multiple countries, scientists spend years putting together the major cross-country collaborations the system requires. Meanwhile, European Research Council grants are “extremely competitive and limited,” de Vries said.

Richard’s NIH grants pay for 65 percent of her salary and for 80 percent of her team, and she believes she’s the most dependent on US funds of anyone in her department at Erasmus Medical Center in Rotterdam. She applied because the NIH funding seemed more sustainable than local money, she said. In Europe, too often funding is short-term and has a time-consuming administrative burden, she said, which hinders researchers from developing long-term plans. “We have to battle so much to just do our work and find funds to just do our basic work,” she said. “I think we need to advocate for a better and more sustainable way of funding research.”

Scientists, too, are worried about what US cuts mean for global science, beyond the short-term. Paltry science funding could discourage a generation of talented people from entering the field, Pfister suggested: “In the end, the resources are not only monetary, but also the brain resources are reduced.”

Let’s not talk about it

A few months ago, Pfister attended a summit in Boston for Cancer Grand Challenges, a research initiative co-funded by the NIH’s National Cancer Institute and Cancer Research U.K. Nobody from the NIH came because they had no funding to travel. “So we are all sitting in Boston, and they are sitting like 200 miles away,” he said.

More concerning was the fact that those present seemed afraid to discuss why the NIH staff were absent, he said. “It was us Europeans to basically, kind of break the ice to, you know, at least talk about it.”

Pfister said that some European researchers are now hesitant about embarking on US collaborations, even if there is funding available. And some German scientists are taking steps to ensure that they are protected if a similar budget crackdown occurred in Germany, he said—devising independent review processes, separating research policy from funding, and developing funding models less dependent on government-only sources, he said. “I think the most scary part is that you know, this all happened in three months.”

Despite the worry and uncertainty, de Vries offered a hopeful view of the future. “We will not be defeated by NIH cuts,” he said. “I feel confident that Europe will organize itself.”

This article was originally published on Undark. Read the original article.

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Ars reflects on Apollo 13 turning 30

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Ron Howard’s 1995 love letter to NASA’s Apollo program takes a few historical liberties but it still inspires awe.

Credit: Universal Pictures

This year marks the 30th anniversary of the 1995 Oscar-winning film, Apollo 13, director Ron Howard’s masterful love letter to NASA’s Apollo program in general and the eponymous space mission in particular. So we’re taking the opportunity to revisit this riveting homage to American science, ingenuity, and daring.

(Spoilers below.)

Apollo 13 is a fictional retelling of the aborted 1970 lunar mission that became a “successful failure” for NASA because all three astronauts made it back to Earth alive against some pretty steep odds. The film opens with astronaut Jim Lovell (Tom Hanks) hosting a watch party in July 1969 for Neil Armstrong’s historic first walk on the Moon. He is slated to command the Apollo 14 mission, and is ecstatic when he and his crew—Ken Mattingly (Gary Sinise) and Fred Haise (Bill Paxton)—are bumped to Apollo 13 instead. His wife, Marilyn (Kathleen Quinlan) is more superstitious and hence less thrilled: “It had to be 13.” To which her pragmatic husband replies, “It comes after 12.”

A few days before launch, Mattingly is grounded because he was exposed to the measles and replaced with backup Jack Swigert (Kevin Bacon), who is the only one happy about the situation. But Lovell and Haise rebound from the disappointment and the launch goes off without a hitch. The public, alas, just isn’t interested in what they think has become routine. But the mission is about to become anything but that.

During a maintenance task to stir the oxygen tanks, an electrical short causes one of the tanks to explode, with the other rapidly venting its oxygen into space. The crew has less than an hour to evacuate the command module Odyssey into the lunar module Aquarius, using it as a lifeboat. There is no longer any chance of landing on the Moon; the new mission is to keep the astronauts alive long enough to figure out how to bring them safely home. That means overcoming interpersonal tensions, freezing conditions, dwindling rations, and unhealthy CO2 levels, among other challenges, as well as taking on a pulse-pounding manual course correction with no navigational computer. (Spoiler alert: they make it!)

The Apollo 13 crew: Jim Lovell (Tom Hanks), Jack Swigert (Kevin Bacon), and Fred Haise (Bill Paxton). Universal Pictures

The film is loosely based on Lovell’s 1994 memoir, Lost Moon. While Lovell initially hoped Kevin Costner would portray him, Howard ultimately cast Hanks in the role, in part because the latter already had extensive knowledge of the Apollo program and space history. Hanks, Paxton, and Bacon all went to US Space Camp to prepare for their roles, participating in astronaut training exercises and flying on the infamous “Vomit Comet” (the KC-135) to experience simulated weightlessness. Howard ultimately shot most of the weightless scenes aboard the KC-135 since recreating those conditions on a soundstage and with CGI would have been prohibitively expensive.

In fact, Howard didn’t rely on archival mission footage at all, insisting on shooting his own footage. That meant constructing realistic spacecraft interiors—incorporating some original Apollo materials—and reproducing exactly the pressure suits worn by astronauts. (The actors, once locked in, breathed air pumped into the suits just like the original Apollo astronauts.) The Mission Control set at Universal Studios was so realistic that one NASA consultant kept looking for the elevator when he left each day, only to remember he was on a movie set.

The launch sequence was filmed using miniature models augmented with digital image stitching. Ditto for the splashdown, in which actual parachutes and a prop capsule were tossed out of a helicopter to shoot the scene. Only the exhaust from the attitude control thrusters was generated with CGI. A failed attempt at using CGI for the in-space urine dump was scrapped in favor of just spraying droplets from an Evian bottle.

It all paid off in the end. Apollo 13 premiered on June 30, 1995, to critical acclaim and racked up over $355 million globally at the box office. It was nominated for nine Oscars and won two—Best Film Editing and Best Sound—although it lost Best Picture to another Hanks film, Forrest Gump. (We can’t quite believe it either.) And the film has stood the test of time, capturing the essence of America’s early space program for posterity. A few Ars staffers shared their thoughts on Apollo 13‘s enduring legacy.

Failure should be an option

White Team Flight Director Gene Krantz (Ed Harris) insists, “We are not losing those men!” Universal Pictures

The tagline for Apollo 13 is “Failure is not an option.” But this is a bit of Hollywood magic. It turns out that NASA Flight Director Gene Kranz never said the line during the actual Apollo 13 mission to the Moon, or the subsequent efforts to save the crew.

Instead the line was conceived after the script writers, Al Reinert and Bill Broyles, interviewed Kranz at his home Texas, south of Johnson Space Center. They were so taken by the notion it became synonymous with the film and with Kranz himself, one of NASA most storied flight directors. He has lived with the line in the decades since, and embraced it by using it as the title of his autobiography. Ever since then the public has associated the idea that NASA would never accept failure with the space agency.

Of course it is great that the public believes so strongly in NASA. But this also turned out to be a millstone around the agency’s neck. This is not really the fault of Kranz. However, as the public became unaccepting of failure, so did Congress, and NASA’s large programs became intolerant of failure. This is one of the reasons why the timeline and cost of NASA’s rockets and spacecraft and interplanetary missions have ballooned. There are so many people looking for things that could possibly go wrong, the people actually trying to build hardware and fly missions are swamped by requirements.

This is why companies like SpaceX, with an iterative design methodology that accepts some level of failure in order to go more quickly, have thrived. They have moved faster, and at significantly less cost, than the government. I asked Kranz about this a few years ago, the idea that NASA (and its Congressional paymasters) should probably be a little more tolerant of failure.

“Space involves risk, and I think that’s the one thing about Elon Musk and all the various space entrepreneurs: they’re willing to risk their future in order to accomplish the objective that they have decided on,” he told me. “I think we as a nation have to learn that, as an important part of this, to step forward and accept risk.”

—Eric Berger

The perfect gateway drug

“Gentlemen, that’s not good enough.” Universal Pictures

Technically I am a child of the ’60s (early Gen-X), but I was far too young to grasp the significance of the Apollo 11 moon landing in 1969, or just how impressive NASA’s achievement really was. The adults made us sit around the TV in our PJs and seemed very excited about the grainy picture. That’s it. That’s all I remember. My conscious knowledge of space exploration was more influenced by Star Wars and the 1986 Challenger explosion. So going to see Apollo 13 in 1995 as a young science writer was a revelation. I walked out of the theater practically vibrating with excitement, turned to my friends and exclaimed, “Oh my god, we went to the Moon in a souped-up Buick!”

Apollo 13 makes space exploration visceral, makes the audience feel like they are right there in the capsule with the crew battling the odds to get back home. It perfectly conveys the huge risks and stalwart courage of everyone involved in the face of unimaginable pressure. Nerds are the heroes and physics and math are critical: I love the scene where Lovell has to calculate gimbal conversions by hand and asks mission control to check his work. A line of men with slide rules feverishly make their own calculations and one-by-one give the thumbs up.

Then there’s the pragmatic ingenuity of the engineers who had to come up with a way to fit square air filters into a round hole using nothing but items already onboard the spacecraft. There’s a reason I rewatch Apollo 13 every couple of years when I’m in the mood for a “let’s work the problem, people” pick-me-up. (Shoutout to Lovell’s mother, Blanche—played by Howard’s mother, the late Jean Speegle Howard—and her classic line: “If they could get a washing machine to fly, my Jimmy could land it.”)

Naturally, Howard had to sacrifice some historical accuracy in the name of artistic license, sparking the inevitable disgruntled griping among hardcore space nerds. For instance, the mission’s original commander, Alan Shepard, wasn’t grounded because of an ear infection but by Meniere’s disease (an inner ear issue that can cause dizziness). Mission control didn’t order the shutdown of the fuel cells; they were already dead. Swigert and Haise didn’t really argue about who was to blame for the accident. And the film ignores the critical role of Flight Director Glynn Lunney and his Black Team (among others), choosing to focus on Kranz’s White Team to keep the story streamlined.

Look, I get it: nobody wants to see a topic they’re passionate about misrepresented in a movie. But there’s no question that thanks to Howard’s narrative instincts, the film continues to resonate with the general public in ways that a by-the-book docudrama obsessing over the tiniest technical details never could.

In the grand scheme of things, that matters far more than whether Lovell really said, “Houston, we have a problem” in those exact words.  If you want the public to support space exploration and—crucially—for Congress to fund it, you need to spark their imaginations and invite them to share in the dream. Apollo 13 is the perfect gateway drug for future space fans, who might find themselves also vibrating with excitement afterward, so inspired by the film that they decide they want to learn more—say, by watching the 12-part Emmy-winning docuseries From the Earth to the Moon that Howard and Hanks co-produced (which is historically accurate). And who knows? They might even decide they want to be space explorers themselves one day.

—Jennifer Ouellette

A common touchstone

Lift-off! Universal Pictures

My relationship with Apollo 13 is somewhat different from most folks: I volunteer as a docent at Space Center Houston, the visitor’s center for Houston’s Johnson Space Center. Specifically, I’m an interpretive guide for the center’s Saturn V exhibit—the only one of the three remaining Saturn V exhibits in the world composed of tip-to-tip of flight stages.

I reference Apollo 13 constantly during guide shifts because it’s a common touchstone that I can count on most folks visiting SCH to have seen, and it visually explicates so many of the more technical aspects of the Apollo program. If I’m explaining that the near-avalanche of white stuff one sees falling off of a Saturn V at launch is actually ice (the rocket’s cryogenic fuels are fantastically cold, and the launch pad at Florida is usually warm and humid, so ice forms on the rocket’s outer skin over the liquid oxygen and liquid hydrogen tanks as it sits on the pad), I reference the launch scene in the movie. If I’m explaining the transposition and docking maneuver by which the Apollo command module docked with and extracted the lunar module from its little garage, I reference the T&D scene in the movie.

Questions about breathing and carbon dioxide? Movie scene. The well-known tension between the astronaut corps and the flight surgeons? Movie scene. And the list goes on. It’s the most amazing reference material I could possibly have.

The film has its detractors, of course, and most geeks wanting to take issue with it will fire shots at the film’s historical accuracy. (Apollo EECOM Sy Liebergot, played in the film by director Ron Howard’s brother Clint, griped once to me that the movie had the audacity to depict the Apollo spacecraft’s trans-lunar injection burn as occurring with the Moon visible in the windows instead of on the far side of the planet—an apparently unforgivable astronavigational sin.) The movie amps up the drama in all respects, adds dialog no astronaut or controller would say, mashes people together into composite characters, compresses or expands the timelines of many of the events in the mission, shows many of those same events happening out of order, and puts people (like Gary Sinise’s Ken Mattingly) in places and roles they were never in.

All these things are true—but they’re also necessary additions in order to get one’s hands around a messy historical event (an event, like all events, that was basically just a whole bunch of stuff all happening at the same time) and fit it into a three-act structure that preserves the important things and that non-technical non-astronaut audiences can follow and understand. And the film succeeds brilliantly, telling a tale that both honors the historicity and technical details of the mission, and that also continues to function as a powerful interpretive tool that teaches people even 35 years after release.

Is every button pressed in the right way? No. Does it bug the crap out of me every time Kevin Bacon answers Tom Hanks’ “How’s the alignment?” question by nonsensically saying “GDC align” and pressing the GDC align button, which is neither what Lovell was asking nor the proper procedure to get the answer Lovell was looking for? Yes. But’s also pure competence porn—an amazing love letter to the space program and the 400,000 men and women who put humans on the Moon.

And like Lovell says: “It’s not a miracle. We just decided to go.”

—Lee Hutchinson

Photo of Jennifer Ouellette

Jennifer is a senior writer at Ars Technica with a particular focus on where science meets culture, covering everything from physics and related interdisciplinary topics to her favorite films and TV series. Jennifer lives in Baltimore with her spouse, physicist Sean M. Carroll, and their two cats, Ariel and Caliban.

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A neural brain implant provides near instantaneous speech

Biology, brain implants, neurobiology, neuroprosthesis, Science, Speech / /

Focusing on sound production instead of word choice makes for a flexible system.

The participant’s implant gets hooked up for testing. Credit: UC Regents

Stephen Hawking, a British physicist and arguably the most famous man suffering from amyotrophic lateral sclerosis (ALS), communicated with the world using a sensor installed in his glasses. That sensor used tiny movements of a single muscle in his cheek to select characters on a screen. Once he typed a full sentence at a rate of roughly one word per minute, the text was synthesized into speech by a DECtalk TC01 synthesizer, which gave him his iconic, robotic voice.

But a lot has changed since Hawking died in 2018. Recent brain-computer-interface (BCI) devices have made it possible to translate neural activity directly into text and even speech. Unfortunately, these systems had significant latency, often limiting the user to a predefined vocabulary, and they did not handle nuances of spoken language like pitch or prosody. Now, a team of scientists at the University of California, Davis has built a neural prosthesis that can instantly translate brain signals into sounds—phonemes and words. It may be the first real step we have taken toward a fully digital vocal tract.

Text messaging

“Our main goal is creating a flexible speech neuroprosthesis that enables a patient with paralysis to speak as fluently as possible, managing their own cadence, and be more expressive by letting them modulate their intonation,” says Maitreyee Wairagkar, a neuroprosthetics researcher at UC Davis who led the study. Developing a prosthesis ticking all these boxes was an enormous challenge because it meant Wairagkar’s team had to solve nearly all the problems BCI-based communication solutions have faced in the past. And they had quite a lot of problems.

The first issue was moving beyond text—most successful neural prostheses developed so far have translated brain signals into text—the words a patient with an implanted prosthesis wanted to say simply appeared on a screen. Francis R. Willett led a team at Stanford University that achieved brain-to-text translation with around a 25 percent error rate. “When a woman with ALS was trying to speak, they could decode the words. Three out of four words were correct. That was super exciting but not enough for daily communication,” says Sergey Stavisky, a neuroscientist at UC Davis and a senior author of the study.

Delays and dictionaries

One year after the Stanford work, in 2024, Stavisky’s team published its own research on a brain-to-text system that bumped the accuracy to 97.5 percent. “Almost every word was correct, but communicating over text can be limiting, right?” Stavisky said. “Sometimes you want to use your voice. It allows you to make interjections, it makes it less likely other people interrupt you—you can sing, you can use words that aren’t in the dictionary.” But the most common approach to generating speech relied on synthesizing it from text, which led straight into another problem with BCI systems: very high latency.

In nearly all BCI speech aids, sentences appeared on a screen after a significant delay, long after the patient finished stringing the words together in their mind. The speech synthesis part usually happened after the text was ready, which caused even more delay. Brain-to-text solutions also suffered from a limited vocabulary. The latest system of this kind supported a dictionary of roughly 1,300 words. When you tried to speak a different language, use more elaborate vocabulary, or even say the unusual name of a café just around the corner, the systems failed.

So, Wairagkar designed her prosthesis to translate brain signals into sounds, not words—and do it in real time.

Extracting sound

The patient who agreed to participate in Wairagkar’s study was codenamed T15 and was a 46-year-old man suffering from ALS. “He is severely paralyzed and when he tries to speak, he is very difficult to understand. I’ve known him for several years, and when he speaks, I understand maybe 5 percent of what he’s saying,” says David M. Brandman, a neurosurgeon and co-author of the study. Before working with the UC Davis team, T15 communicated using a gyroscopic head mouse to control a cursor on a computer screen.

To use an early version of Stavisky’s brain-to-text system, the patient had 256 microelectrodes implanted into his ventral precentral gyrus, an area of the brain responsible for controlling vocal tract muscles.

For the new brain-to-speech system, Wairagkar and her colleagues relied on the same 256 electrodes. “We recorded neural activities from single neurons, which is the highest resolution of information we can get from our brain,” Wairagkar says. The signal registered by the electrodes was then sent to an AI algorithm called a neural decoder that deciphered those signals and extracted speech features such as pitch or voicing. In the next step, these features were fed into a vocoder, a speech synthesizing algorithm designed to sound like the voice that T15 had when he was still able to speak normally. The entire system worked with latency down to around 10 milliseconds—the conversion of brain signals into sounds was effectively instantaneous.

Because Wairagkar’s neural prosthesis converted brain signals into sounds, it didn’t come with a limited selection of supported words. The patient could say anything he wanted, including pseudo-words that weren’t in a dictionary and interjections like “um,” “hmm,” or “uh.” Because the system was sensitive to features like pitch or prosody, he could also vocalize questions saying the last word in a sentence with a slightly higher pitch and even sing a short melody.

But Wairagkar’s prosthesis had its limits.

Intelligibility improvements

To test the prosthesis’s performance, Wairagkar’s team first asked human listeners to match a recording of some synthesized speech by the T15 patient with one transcript from a set of six candidate sentences of similar length. Here, the results were completely perfect, with the system achieving 100 percent intelligibility.

The issues began when the team tried something a bit harder: an open transcription test where listeners had to work without any candidate transcripts. In this second test, the word error rate was 43.75 percent, meaning participants identified a bit more than half of the recorded words correctly. This was certainly an improvement compared to the intelligibility of the T15’s unaided speech where the word error in the same test with the same group of listeners was 96.43 percent. But the prosthesis, while promising, was not yet reliable enough to use it for day-to-day communication.

“We’re not at the point where it could be used in open-ended conversations. I think of this as a proof of concept,” Stavisky says. He suggested that one way to improve future designs would be to use more electrodes. “There are a lot of startups right now building BCIs that are going to have over a thousand electrodes. If you think about what we’ve achieved with just 250 electrodes versus what could be done with a thousand or two thousand—I think it would just work,” he argued. And the work to make that happen is already underway.

Paradromics, a BCI-focused startup based in Austin, Texas, wants to go ahead with clinical trials of a speech neural prosthesis and is already seeking FDA approval. “They have a 1,600 electrode system, and they publicly stated they are going to do speech,” Stavisky says. “David Brandman, our co-author, is going to be the lead principal investigator for these trials, and we’re going to do it here at UC Davis.”

Nature, 2025.  DOI: 10.1038/s41586-025-09127-3

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Jacek Krywko is a freelance science and technology writer who covers space exploration, artificial intelligence research, computer science, and all sorts of engineering wizardry.

A neural brain implant provides near instantaneous speech Read More »

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Robotic sucker can adapt to surroundings like an actual octopus

Biology, octopus, robotics, Science / /

This isn’t the first time suction cups were inspired by highly adaptive octopus suckers. Some models have used pressurized chambers meant to push against a surface and conform to it. Others have focused more on matching the morphology of a biological sucker. This has included giving the suckers microdenticles, the tiny tooth-like projections on octopus suckers that give them a stronger grip.

Previous methods of artificial conformation have had some success, but they could be prone to leakage from gaps between the sucker and the surface it is trying to stick to, and they often needed vacuum pumps to operate. Yue and his team created a sucker that was morphologically and mechanically similar to that of an octopus.

Suckers are muscular structures with an extreme flexibility that helps them conform to objects without leakage, contract when gripping objects, and release tension when letting them go. This inspired the researchers to create suckers from a silicone sponge material on the inside and a soft silicone pad on the outside.

For the ultimate biomimicry, Yue thought that the answer to the problems experienced with previous models was to come up with a sucker that simulated the mucus secretion of octopus suckers.

This really sucks

Cephalopod suction was previously thought to be a product of these creatures’ soft, flexible bodies, which can deform easily to adapt to whatever surface it needs to grip. Mucus secretion was mostly overlooked until Yue decided to incorporate it into his robo-suckers.

Mollusk mucus is known to be five times more viscous than water. For Yue’s suckers, an artificial fluidic system, designed to mimic the secretions released by glands on a biological sucker, creates a liquid seal between the sucker and the surface it is adhering to, just about eliminating gaps. It might not have the strength of octopus slime, but water is the next best option for a robot that is going to be immersed in water when it goes exploring, possibly in underwater caves or at the bottom of the ocean.

Robotic sucker can adapt to surroundings like an actual octopus Read More »

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Rocket Report: SpaceX’s dustup on the border; Northrop has a nozzle problem

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NASA has finally test-fired the first of its new $100 million SLS rocket engines.

Backdropped by an offshore thunderstorm, a SpaceX Falcon 9 booster stands on its landing pad at Cape Canaveral after returning to Earth from a mission launching four astronauts to the International Space Station early Wednesday. Credit: SpaceX

Welcome to Edition 7.50 of the Rocket Report! We’re nearly halfway through the year, and it seems like a good time to look back on the past six months. What has been most surprising to me in the world of rockets? First, I didn’t expect SpaceX to have this much trouble with Starship Version 2. Growing pains are normal for new rockets, but I expected the next big hurdles for SpaceX to clear with Starship to be catching the ship from orbit and orbital refueling, not completing a successful launch. The state of Blue Origin’s New Glenn program is a little surprising to me. New Glenn’s first launch in January went remarkably well, beating the odds for a new rocket. Now, production delays are pushing back the next New Glenn flights. The flight of Honda’s reusable rocket hopper also came out of nowhere a few weeks ago.

As always, we welcome reader submissions. If you don’t want to miss an issue, please subscribe using the box below (the form will not appear on AMP-enabled versions of the site). Each report will include information on small-, medium-, and heavy-lift rockets, as well as a quick look ahead at the next three launches on the calendar.

Isar raises 150 million euros. German space startup Isar Aerospace has obtained 150 million euros ($175 million) in funding from an American investment company, Reuters reports. The company, which specializes in satellite launch services, signed an agreement for a convertible bond with Eldridge Industries, it said. Isar says it will use the funding to expand its launch service offerings. Isar’s main product is the Spectrum rocket, a two-stage vehicle designed to loft up to a metric ton (2,200 pounds) of payload mass to low-Earth orbit. Spectrum flew for the first time in March, but it failed moments after liftoff and fell back to the ground near its launch pad. Still, Isar became the first in a new crop of European launch startups to launch a rocket theoretically capable of reaching orbit.

Flush with cash … Isar is leading in another metric, too. The Munich-based company has now raised more than 550 million euros ($642 million) from venture capital investors and government-backed funds. This far exceeds the fundraising achievements of any other European launch startup. But the money will only go so far before Isar must prove it can successfully launch a rocket into orbit. Company officials have said they aim to launch the second Spectrum rocket before the end of this year. (submitted by EllPeaTea)

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Rocket Lab aiming for record turnaround. Rocket Lab demonstrated a notable degree of flexibility this week. Two light-class Electron rockets were nearing launch readiness at the company’s privately owned spaceport in New Zealand, but one of the missions encountered a technical problem, and Rocket Lab scrubbed a launch attempt Tuesday. The spaceport has two launch pads next to one another, so while technicians worked to fix that problem, Rocket Lab slotted in another Electron rocket to lift off from the pad next door. That mission, carrying a quartet of small commercial signals intelligence satellites for HawkEye 360, successfully launched Thursday.

Giving it another go … A couple of hours after that launch, Rocket Lab announced it was ready to try again with the mission it had grounded earlier in the week. “Can’t get enough of Electron missions? How about another one tomorrow? With our 67th mission complete, we’ve scheduled our next launch from LC-1 in less than 48 hours—Electron’s fastest turnaround from the same launch site yet!” Rocket Lab hasn’t disclosed what satellite is flying on this mission, citing the customer’s preference to remain anonymous for now.

You guessed it! Baguette One will launch from France. French rocket builder HyPrSpace will launch its Baguette One demonstrator from a missile testing site in mainland France, after signing an agreement with the country’s defense procurement agency, European Spaceflight reports. HyPrSpace was founded in 2019 to begin designing an orbital-class rocket named Orbital Baguette 1 (OB-1). The Baguette One vehicle is a subscale, single-stage suborbital demonstrator to prove out technologies for the larger satellite launcher, mainly its hybrid propulsion system.

Sovereign launch … HyPrSpace’s Baguette One will stand roughly 10 meters (30 feet) tall and will be capable of carrying payloads of up to 300 kilograms (660 pounds) to suborbital space. It is scheduled to launch next year from a French missile testing site in the south of France. “Gaining access to this dual-use launch pad in mainland France is a major achievement after many years of work on our hybrid propulsion technology,” said Sylvain Bataillard, director general of HyPrSpace. “It’s a unique opportunity for HyPrSpace and marks a decisive turning point. We’re eager to launch Baguette One and to play a key role in building a more sovereign, more sustainable, and boldly innovative European dual-use space industry.” (submitted by EllPeaTea)

Firefly moves closer to launching from Sweden. An agreement between the United States and Sweden brings Firefly Aerospace one step closer to launching its Alpha rocket from a Swedish spaceport, Space News reports. The two countries signed a technology safeguards agreement (TSA) at a June 20 ceremony at the Swedish embassy in Washington, DC. The TSA allows the export of American rockets to Sweden for launches there, putting in place measures to protect launch vehicle technology.

A special relationship … The US government has signed launch-related safeguard agreements with only a handful of countries, such as Australia, the United Kingdom, and now Sweden. Rocket exports are subject to strict controls because of the potential military applications of that technology. Firefly currently launches its Alpha rocket from Vandenberg Space Force Base, California, and is building a launch site at Wallops Island, Virginia. Firefly also has a lease for a launch pad at Cape Canaveral, Florida, although the company is prioritizing other sites. Then, last year, Firefly announced an agreement with the Swedish Space Corporation to launch Alpha from Esrange Space Center as soon as 2026. (submitted by EllPeaTea)

Amazon is running strong out of the gate. For the second time in two months, United Launch Alliance sent a batch of 27 broadband Internet satellites into orbit for Amazon on Monday morning, Ars reports. This was the second launch of a full load of operational satellites for Amazon’s Project Kuiper, a network envisioned to become a competitor to SpaceX’s Starlink. Just like the last flight on April 28, an Atlas V rocket lifted off from Cape Canaveral, Florida, and delivered Amazon’s satellites into an on-target orbit roughly 280 miles (450 kilometers) above Earth.

Time to put up or shut up … After lengthy production delays at Amazon’s satellite factory, the retail giant is finally churning out Kuiper satellites at scale. Amazon has already shipped the third batch of Kuiper satellites to Florida to prepare for launch on a SpaceX Falcon 9 rocket next month. ULA won the lion’s share of Amazon’s multibillion-dollar launch contract in 2022, committing to up to 38 Vulcan launches for Kuiper and nine Atlas V flights. Three of those Atlas Vs have now launched. Amazon also reserved 18 launches on Europe’s Ariane 6 rocket, and at least 12 on Blue Origin’s New Glenn. Vulcan, Ariane 6, and New Glenn have only flown one or two times, and Amazon is asking them to quickly ramp up their cadence to deliver 3,232 Kuiper satellites to orbit in the next few years. The handful of Falcon 9s and Atlas Vs that Amazon has on contract are the only rockets in the bunch with a proven track record. With Kuiper satellites now regularly shipping out of the factory, any blame for future delays may shift from Amazon to the relatively unproven rockets it has chosen to launch them.

Falcon 9 launches with four commercial astronauts. Retired astronaut Peggy Whitson, America’s most experienced space flier, and three rookie crewmates from India, Poland, and Hungary blasted off on a privately financed flight to the International Space Station early Wednesday, CBS News reports. This is the fourth non-government mission mounted by Houston-based Axiom Space. The four commercial astronauts rocketed into orbit on a SpaceX Falcon 9 launcher from NASA’s Kennedy Space Center in Florida, and their Dragon capsule docked at the space station Thursday to kick off a two-week stay.

A brand-new Dragon … The Crew Dragon spacecraft flown on this mission, serial number C213, is the fifth and final addition to SpaceX’s fleet of astronaut ferry ships built for NASA trips to the space station and for privately funded commercial missions to low-Earth orbit. Moments after reaching orbit Wednesday, Whitson revealed the name of the new spacecraft: Crew Dragon Grace. “We had an incredible ride uphill, and now we’d like to set our course for the International Space Station aboard the newest member of the Dragon fleet, our spacecraft named Grace. … Grace reminds us that spaceflight is not just a feat of engineering, but an act of goodwill to the benefit of every human everywhere.”

How soon until Ariane 6 is flying regularly? It’ll take several years for Arianespace to ramp up the launch cadence of Europe’s new Ariane 6 rocket, Space News reports. David Cavaillolès, chief executive of Arianespace, addressed questions at the Paris Air Show about how quickly Arianespace can reach its target of launching 10 Ariane 6 rockets per year. “We need to go to 10 launches per year for Ariane 6 as soon as possible,” he said. “It’s twice as more as for Ariane 5, so it’s a big industrial change.” Two Ariane 6 rockets have launched so far, and a third mission is on track to lift off in August. Arianespace’s CEO reiterated earlier plans to conduct four more Ariane 6 launches through the end of this year, including the first flight of the more powerful Ariane 64 variant with four solid rocket boosters.

Not a heavy lift … Arianespace’s target flight rate of 10 Ariane 6 rockets per year is modest compared to other established companies with similarly sized launch vehicles. United Launch Alliance is seeking to launch as many as 25 Vulcan rockets per year. Blue Origin’s New Glenn is designed to eventually fly often, although the company hasn’t released a target launch cadence. SpaceX, meanwhile, aims to launch up to 170 Falcon 9 rockets this year. But European governments are perhaps more committed than ever to maintaining a sovereign launch capability for the continent, so Ariane 6 isn’t going away. Arianespace has sold more than 30 Ariane 6 launches, primarily to European institutional customers and Amazon.

SLS booster blows its nozzle. NASA and Northrop Grumman test-fired a new solid rocket booster in Utah on Thursday, and it didn’t go exactly according to plan, Ars reports. This booster features a new design that NASA would use to power Space Launch System rockets, beginning with the ninth mission, or Artemis IX. The motor tested on Thursday isn’t flight-worthy. It’s a test unit that engineers will use to learn about the rocket’s performance. It turns out they did learn something, but perhaps not what they wanted. About 1 minute and 40 seconds into the booster’s burn, a fiery plume emerged from the motor’s structure just above its nozzle. Moments later, the nozzle violently disintegrated. The booster kept firing until it ran out of pre-packed solid propellant.

A questionable future … NASA’s Space Launch System appears to have a finite shelf life. The Trump administration wants to cancel it after just three launches, while the preliminary text of a bill making its way through Congress would extend it to five flights. But chances are low the Space Launch System will make it to nine flights, and if it does, it’s questionable if it would reach that point before 2040. The SLS rocket is a core piece of NASA’s plan to return US astronauts to the Moon under the Artemis program, but the White House seeks to cancel the program in favor of cheaper commercial alternatives.

NASA conducts a low-key RS-25 engine test. The booster ground test on Thursday was the second time in less than a week that NASA test-fired new propulsion hardware for the Space Launch System. Last Friday, June 20, NASA ignited a new RS-25 engine on a test stand at Stennis Space Center in Mississippi. The hydrogen-fueled engine is the first of its kind to be manufactured since the end of the space shuttle program. This particular RS-25 engine is assigned to power the fifth launch of the SLS rocket, a mission known as Artemis V, that may end up never flying. While NASA typically livestreams engine tests at Stennis, the agency didn’t publicize this event ahead of time.

It has been 10 years … The SLS rocket was designed to recycle leftover parts from the space shuttle program, but NASA will run out of RS-25 engines after the rocket’s fourth flight and will exhaust its inventory of solid rocket booster casings after the eighth flight. Recognizing that shuttle-era parts will eventually run out, NASA signed a contract with Aerojet Rocketdyne (now L3Harris) to set the stage for the production of new RS-25 engines in 2015. NASA later ordered an initial batch of six RS-25 engines from Aerojet, then added 18 more to the order in 2020, at a price of about $100 million per engine. Finally, a brand-new flight-worthy RS-25 engine has fired up on a test stand. If the Trump administration gets its way, these engines will never fly. Maybe that’s fine, but after so long with so much taxpayer investment, last week’s test milestone is worth publicizing, if not celebrating.

SpaceX finds itself in a dustup on the border. President Claudia Sheinbaum of Mexico is considering taking legal action after one of SpaceX’s giant Starship rockets disintegrated in a giant fireball earlier this month as it was being fueled for a test-firing of its engines, The New York Times reports. No one was injured in the explosion, which rained debris on the beaches of the northern Mexican state of Tamaulipas. The conflagration occurred at a test site SpaceX operates a few miles away from the Starship launch pad. This test facility is located next to the Rio Grande River, just a few hundred feet from Mexico. The power of the blast sent wreckage flying across the river into Mexican territory.

Collision course …“We are reviewing everything related to the launching of rockets that are very close to our border,” Sheinbaum said at a news conference Wednesday. If SpaceX violated any international laws, she added, “we will file any necessary claims.” Sheinbaum’s leftist party holds enormous sway around Mexico, and the Times reports she was responding to calls to take action against SpaceX amid a growing outcry among scientists, regional officials, and environmental activists over the impact that the company’s operations are having on Mexican ecosystems. SpaceX, on the other hand, said its efforts to recover debris from the Starship explosion have been “hindered by unauthorized parties trespassing on private property.” SpaceX said it requested assistance from the government of Mexico in the recovery and added that it offered its own resources to help with the cleanup.

Next three launches

June 28: Falcon 9 | Starlink 10-34 | Cape Canaveral Space Force Station, Florida | 04: 26 UTC

June 28: Electron | “Symphony in the Stars” | Māhia Peninsula, New Zealand | 06: 45 UTC

June 28: H-IIA | GOSAT-GW | Tanegashima Space Center, Japan | 16: 33 UTC

Photo of Stephen Clark

Stephen Clark is a space reporter at Ars Technica, covering private space companies and the world’s space agencies. Stephen writes about the nexus of technology, science, policy, and business on and off the planet.

Rocket Report: SpaceX’s dustup on the border; Northrop has a nozzle problem Read More »

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NASA tested a new SLS booster that may never fly, and the end of it blew off

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NASA didn’t want to say much about one of the tests, and the other one lost its nozzle.

An uncontained plume of exhaust appeared near the nozzle of an SLS solid rocket booster moments before its nozzle was destroyed during a test-firing Thursday. Credit: NASA

NASA’s Space Launch System appears to have a finite shelf life. The Trump administration wants to cancel it after just three launches, while the preliminary text of a bill making its way through Congress would extend it to five flights.

But chances are low the Space Launch System will make it to nine flights, and if it does, it’s questionable that it would reach that point before 2040. The SLS rocket is a core piece of NASA’s plan to return US astronauts to the Moon under the Artemis program, but the White House seeks to cancel the program in favor of cheaper commercial alternatives.

For the second time in less than a week, NASA test-fired new propulsion hardware Thursday that the agency would need to keep SLS alive. Last Friday, a new liquid-fueled RS-25 engine ignited on a test stand at NASA’s Stennis Space Center in Mississippi. The hydrogen-fueled engine is the first of its kind to be manufactured since the end of the Space Shuttle program. This particular RS-25 engine is assigned to power the fifth flight of the SLS rocket, a mission known as Artemis V.

Then, on Thursday of this week, NASA and Northrop Grumman test-fired a new solid rocket booster in Utah. This booster features a new design that NASA would use to power SLS rockets beginning with the ninth mission, or Artemis IX. The motor tested on Thursday isn’t flight-worthy. It’s a test unit that engineers will use to gather data on the rocket’s performance.

While the engine test in Mississippi apparently went according to plan, the ground firing of the new solid rocket booster didn’t go quite as smoothly. Less than two minutes into the burn, the motor’s exhaust nozzle violently shattered into countless shards of debris. You can watch the moment in the YouTube video below.

At the start of the program nearly 15 years ago, NASA and its backers in Congress pitched the SLS rocket as the powerhouse behind a new era of deep space exploration. The Space Launch System, they said, would have the advantage of recycling old space shuttle engines and boosters, fast-tracking the new rocket’s path to the launch pad for less money than the cost of an all-new vehicle.

That didn’t pan out. Each Artemis mission costs $4.2 billion per flight, and that’s with shuttle-era engines and boosters that NASA and its contractors already have in their inventories. NASA’s 16 leftover shuttle main engines are enough for the first four SLS flights. NASA has leftover parts for eight pairs of solid rocket boosters.

It has been 10 years

Recognizing that shuttle-era parts will eventually run out, NASA signed a contract with Aerojet Rocketdyne to set the stage for the production of new RS-25 engines in 2015. NASA later ordered an initial batch of six RS-25 engines from Aerojet, then added 18 more to the order in 2020, at a price of about $100 million per engine. NASA and its contractor aim to reduce the cost to $70 million per engine, but even that figure is many times the cost of engines of comparable size and power: Blue Origin’s BE-4 and SpaceX’s Raptor.

Finally, NASA test-fired a new flight-rated RS-25 engine for the first time last week at Stennis Space Center. The agency has often provided a livestream of its engine tests at Stennis, but it didn’t offer the public any live video. And this particular test was a pretty big deal. L3Harris, which acquired Aerojet Rocketdyne in 2023, has finally reactivated the RS-25 production line after a decade and billions of dollars of funding.

In fact, NASA made no public statement about the RS-25 test until Monday, and the agency didn’t mention its assignment to fly on the Artemis V mission. If the Trump administration gets its way, the engine will never fly. Maybe that’s fine, but after so long with so much taxpayer investment, this is a milestone worth publicizing, if not celebrating.

L3Harris issued a press release Tuesday confirming the engine’s planned use on the fifth SLS mission. The engine completed a 500-second acceptance test, throttling up to 111 percent of rated thrust, demonstrating more power than engines that flew on the space shuttle or on the first SLS launch in 2022.

A new RS-25 engine, No. 20001, was installed on its test stand in Mississippi earlier this year. Credit: NASA

“This successful acceptance test shows that we’ve been able to replicate the RS-25’s performance and reliability, while incorporating modern manufacturing techniques and upgraded components such as the main combustion chamber, nozzle, and pogo accumulator assembly,” said Kristin Houston, president of space propulsion and power systems at Aerojet Rocketdyne, L3Harris. “Our propulsion technology is key to ensuring the United States leads in lunar exploration, creates a sustained presence on the Moon and does not cede this strategic frontier to other nations.”

The test-firing last Friday came a few days before the 50th anniversary of the first space shuttle main engine test at Stennis on June 24, 1975. That engine carried the serial number 0001. The new RS-25 engine is designated No. 20001.

Watch out

NASA followed last week’s low-key engine test with the test-firing of a solid-fueled booster at Northrop Grumman’s rocket test site in Promontory, Utah, on Thursday. Held in place on its side, the booster produced 3.9 million pounds of thrust, outclassing the power output of the existing boosters assigned to the first eight SLS missions.

Unlike the RS-25 firing at Stennis, NASA chose to broadcast the booster test. Everything appeared to go well until 1 minute and 40 seconds into the burn, when a fiery plume of super-hot exhaust appeared to burn through part of the booster’s structure just above the nozzle. Moments later, the nozzle disintegrated.

Solid rocket boosters can’t be turned off after ignition, and for better or worse, the motor continued firing until it ran out of propellant about 30 seconds later. The rocket sparked a fire in the hills overlooking the test stand.

This was the first test-firing of the Booster Obsolescence and Life Extension (BOLE) program, which aims to develop a higher-performance solid rocket booster for SLS missions. NASA awarded Northrop Grumman a $3.2 billion contract in 2021 to produce boosters with existing shuttle parts for five SLS missions (Artemis IV-VIII), and design, develop, and test a new booster design for Artemis IX.

The boosters produce more than 75 percent of the thrust required to propel the SLS rocket off the launch pad with NASA’s crewed Orion spacecraft on top. Four RS-25 engines power the core stage, collectively generating more than 2 million pounds of thrust.

Northrop Grumman calls the new booster “the largest and most powerful segmented solid rocket motor ever built for human spaceflight.”

One of the most significant changes with the BOLE booster design is that it replaces shuttle-era steel cases with carbon-fiber composite cases. Northrop says the new cases are lighter and stronger. It also replaces the booster’s hydraulic thrust vector control steering system with an electronic system. The propellant packed inside the booster is also different, using a mix that Northrop packs inside its commercial rocket motors instead of the recipe used for the space shuttle.

Northrop Grumman has had a tough time with rocket nozzles in recent years. In 2019, a test motor for the company’s now-canceled Omega rocket lost its nozzle during a test-firing in Utah. Then, last year, a smaller Northrop-made booster flying on United Launch Alliance’s Vulcan rocket lost its nozzle in flight. Vulcan’s guidance system and main engines corrected for the problem, and the rocket still achieved its planned orbit.

Photo of Stephen Clark

Stephen Clark is a space reporter at Ars Technica, covering private space companies and the world’s space agencies. Stephen writes about the nexus of technology, science, policy, and business on and off the planet.

NASA tested a new SLS booster that may never fly, and the end of it blew off Read More »

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Changing one gene can restore some tissue regeneration to mice

Biology, Mice, regeneration, retinoic acid, Science / /

Regeneration is a trick many animals, including lizards, starfish, and octopuses, have mastered. Axolotls, a salamander species originating in Mexico, can regrow pretty much everything from severed limbs, to eyes and parts of brain, to the spinal cord. Mammals, though, have mostly lost this ability somewhere along their evolutionary path. Regeneration persisted, in a limited number of tissues, in just a few mammalian species like rabbits or goats.

“We were trying to learn how certain animals lost their regeneration capacity during evolution and then put back the responsible gene or pathway to reactivate the regeneration program,” says Wei Wang, a researcher at the National Institute of Biological Sciences in Beijing. Wang’s team has found one of those inactive regeneration genes, activated it, and brought back a limited regeneration ability to mice that did not have it before.

Of mice and bunnies

The idea Wang and his colleagues had was a comparative study of how the wound healing process works in regenerating and non-regenerating mammalian species. They chose rabbits as their regenerating mammals and mice as the non-regenerating species. As the reference organ, the team picked the ear pinna. “We wanted a relatively simple structure that was easy to observe and yet composed of many different cell types,” Wang says. The test involved punching holes in the ear pinna of rabbits and mice and tracking the wound-repairing process.

The healing process began in the same way in rabbits and mice. Within the first few days after the injury, a blastema—a mass of heterogeneous cells—formed at the wound site. “Both rabbits and mice will heal the wounds after a few days,” Wang explains. “But between the 10th and 15th day, you will see the major difference.” In this timeframe, the earhole in rabbits started to become smaller. There were outgrowths above the blastema—the animals were producing more tissue. In mice, on the other hand, the healing process halted completely, leaving a hole in the ear.

Changing one gene can restore some tissue regeneration to mice Read More »

testing-ancient-paleolithic-migration-with-a-replica-canoe

Testing ancient Paleolithic migration with a replica canoe

anthropology, Archaeology, experimental archaeology, paleolithic, Science / /

(Left) GPS tracking and modeling of ocean currents toward the end of the experimental voyage. (Right) The team on the water around the time of the left image.

(Left) GPS tracking and modeling of ocean currents toward the end of the experimental voyage. (Right) The team on the water around the time of the left image. Credit: Kaifu et al., 2025/CC-By-ND

At the 30-hour mark, the captain ordered the entire crew to rest, letting the dugout drift freely for a while, which fortunately brought them closer to Yonaguni Island. At hour 40, the island’s silhouette was visible, and over the next five hours, the crew was able to navigate the strong tidal flow along the coast until they reached their landing site: Nama Beach. So the experimental voyage was a success, augmented by the numerical simulations to demonstrate that the boat could make similar voyages from different departure points across both modern and late-Pleistocene oceans.

Granted, it was not possible to recreate Paleolithic conditions perfectly on a modern ocean. The crew first spotted the island because of its artificial lights, although by that time, they were on track navigationally. They were also accompanied by escort ships to ensure the crew’s safety, supplying fresh water twice during the voyage. But the escort ships did not aid with navigation or the dugout captain’s decision-making, and the authors believe that any effects were likely minimal. The biggest difference was the paddlers’ basic modern knowledge of local geography, which helped them develop a navigation plan—an unavoidable anachronism, although the crew did not rely on compasses, GPS, or watches during the voyage.

“Scientists try to reconstruct the processes of past human migrations, but it is often difficult to examine how challenging they really were,” said Kaifu. “One important message from the whole project was that our Paleolithic ancestors were real challengers. Like us today, they had to undertake strategic challenges to advance. For example, the ancient Polynesian people had no maps, but they could travel almost the entire Pacific. There are a variety of signs on the ocean to know the right direction, such as visible land masses, heavenly bodies, swells and winds. We learned parts of such techniques ourselves along the way.”

DOI: “Traversing the Kuroshio: Paleolithic migration across one of the world’s strongest ocean currents,” Science Advances, 2025. 10.1126/sciadv.adv5508  (About DOIs).

DOI: “Palaeolithic seafaring in East Asia: an experimental test of the dugout canoe hypothesis,” Science Advances, 2025. 10.1126/sciadv.adv5507  (About DOIs).

Testing ancient Paleolithic migration with a replica canoe Read More »

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Researchers develop a battery cathode material that does it all

batteries, chemistry, lithium, materials science, Science / /

Battery electrode materials need to do a lot of things well. They need to be conductors to get charges to and from the ions that shuttle between the electrodes. They also need to have an open structure that allows the ions to move around before they reach a site where they can be stored. The storage of lots of ions also causes materials to expand, creating mechanical stresses that can cause the structure of the electrode material to gradually decay.

Because it’s hard to get all of these properties from a single material, many electrodes are composite materials, with one chemical used to allow ions into and out of the electrode, another to store them, and possibly a third that provides high conductivity. Unfortunately, this can create new problems, with breakdowns at the interfaces between materials slowly degrading the battery’s capacity.

Now, a team of researchers is proposing a material that seemingly does it all. It’s reasonably conductive, it allows lithium ions to move around and find storage sites, and it’s made of cheap and common elements. Perhaps best of all, it undergoes self-healing, smoothing out damage across charge/discharge cycles.

High capacity

The research team, primarily based in China, set out to limit the complexity of cathodes. “Conventional composite cathode designs, which typically incorporate a cathode active material, catholyte, and electronic conducting additive, are often limited by the substantial volume fraction of electrochemically inactive components,” the researchers wrote. The solution, they reasoned, was to create an all-in-one material that gets rid of most of these materials.

A number of papers had reported good luck with chlorine-based chemicals, which allowed ions to move readily through the material but didn’t conduct electricity very well. So the researchers experimented with pre-loading one of these materials with lithium. And they focused on iron chloride since it’s a very cheap material.

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Today! Ars Live: What’s up with the sudden surge in temperatures?

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At 1pm on Thursday, we encourage you to join us for a live chat with Zeke Hausfather, a climate scientist and researcher at Berkeley Earth. We’ll talk a bit about how he got into climate science and ended up at Berkeley Earth and the role that organization plays in the world of climate science. It was launched by a physicist who was somewhat skeptical of the work being done by climate scientists, but it has evolved into one of the key groups that does the math needed to track the planet’s temperatures.

For the past couple of years, those temperatures have seen a remarkable rise to record highs, at one point setting a yearlong string where every month set a record for the warmest instance of that month on record. The rise leaves us at risk of exceeding key climate targets much earlier than expected and has left the climate science community scrambling to explain the intensity of the heat. So we plan to ask Zeke a bit about what scientists are thinking about the dramatic nature of these changes, attempts to explore the relationship between temperatures, and things like tipping points and individual weather events.

And all that leads to the key question: What does this tell us about where our climate is likely to go over the rest of this century?

After that, we’d like to turn things over to your questions. Is there anything you’ve always wanted to know about climate science but didn’t know who to ask? Zeke may be your guy—and if not, then he almost certainly knows who is. So please join us for this discussion, happening Thursday, June 26, at 1 pm US Eastern Time.

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During a town hall Wednesday, NASA officials on stage looked like hostages

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A Trump appointee suggests NASA may not have a new administrator until next year.

NASA press secretary Bethany Stevens, acting administrator Janet Petro, chief of staff Brian Hughes, associate administrator Vanessa Wyche, and deputy associate administrator Casey Swails held a town hall with NASA employees Wednesday. Credit: NASA

The four people at the helm of America’s space agency held a town hall meeting with employees Wednesday, fielding questions about downsizing, layoffs, and proposed budget cuts that threaten to undermine NASA’s mission and prestige.

Janet Petro, NASA’s acting administrator, addressed questions from an auditorium at NASA Headquarters in Washington, DC. She was joined by Brian Hughes, the agency’s chief of staff, a political appointee who was formerly a Florida-based consultant active in city politics and in Donald Trump’s 2024 presidential campaign. Two other senior career managers, Vanessa Wyche and Casey Swails, were also on the stage.

They tried to put a positive spin on the situation at NASA. Petro, Wyche, and Swails are civil servants, not Trump loyalists. None of them looked like they wanted to be there. The town hall was not publicized outside of NASA ahead of time, but live video of the event was available—unadvertised—on an obscure NASA streaming website. The video has since been removed.

8 percent down

NASA’s employees are feeling the pain after the White House proposed a budget cut of nearly 25 percent in fiscal year 2026, which begins October 1. The budget request would slash NASA’s topline budget by nearly 25 percent, from $24.8 billion to $18.8 billion. Adjusted for inflation, this would be the smallest NASA budget since 1961, when the first American launched into space.

“The NASA brand is really strong still, and we have a lot of exciting missions ahead of us,” Petro said. “So, I know it’s a hard time that we’re going to be navigating, but again, you have my commitment that I’m here and I will share all of the information that I have when I get it.”

It’s true that NASA employees, along with industry officials and scientists who regularly work with the agency, are navigating through what would most generously be described as a period of great uncertainty. The perception among NASA’s workforce is far darker. “NASA is f—ed,” one current leader in the agency told Ars a few weeks ago, soon after President Trump rescinded his nomination of billionaire businessman and commercial astronaut Jared Isaacman to be the agency’s next administrator.

Janet Petro, NASA’s acting administrator, is seen in 2020 at Kennedy Space Center in Florida. Credit: NASA/Kim Shiflett

Before the White House released its detailed budget proposal in May, NASA and other federal agencies were already scrambling to respond to the Trump administration’s directives to shrink the size of the government. While NASA escaped the mass layoffs of probationary employees that affected other departments, the space agency offered buyouts and incentives for civil servants to retire early or voluntarily leave their posts.

About 900 NASA employees signed up for the first round of the government’s “deferred resignation” program. Casey Swails, NASA’s deputy associate administrator, said Wednesday that number is now up to 1,500 after NASA announced another chance for employees to take the government’s deferred resignation offer. This represents about 8 percent of NASA’s workforce, and the window for employees to apply runs until July 25.

One takeaway from Wednesday’s town hall is that at least some NASA leaders want to motivate more employees to resign voluntarily. Hughes said a “major reason” for luring workers to leave the agency is to avoid “being in a spot where we have to do the involuntary options.”

Rumors of these more significant layoffs, or reductions in force, have hung over NASA for several months. If that happens, workers may not get the incentives the government is offering today to those who leave the agency on their own. Swails said NASA isn’t currently planning any such layoff, although she left the door open for the situation to change: “We’re doing everything we can to avoid going down that path.”

Ultimately, it will depend on how many employees NASA can get to resign on their own. If it’s not enough, layoffs may still be an option.

Many questions, few answers

Nearly all of the questions employees addressed to NASA leadership Wednesday were submitted anonymously, and in writing: When might Trump nominate someone for NASA administrator to take Isaacman’s place? Will any of NASA’s 10 field centers be closed? What is NASA going to do about Trump’s budget proposal, particularly its impact on science missions?

Their responses to these questions, in order: Probably not any time soon, maybe, and nothing.

The Trump administration selected Petro, an engineer and former Army helicopter pilot, to become acting head of NASA on Inauguration Day in January. Bill Nelson, who served as a Florida senator until 2019, resigned the NASA administrator job when former President Biden left the White House.

Petro was previously director of NASA’s Kennedy Space Center since 2021, and before that, she was deputy director of the Florida spaceport for 14 years. She leapfrogged NASA’s top civil servant, associate administrator Jim Free, to become acting administrator in January. Free retired from the agency in February. Before the presidential election last year, Free advocated for the next administration to stay the course with NASA’s Artemis program.

But that’s not what the Trump administration wants to do. The White House seeks to cancel the Space Launch System rocket and Orion spacecraft, both core elements of the Artemis program to return astronauts to the Moon after two more flights. Under the new plan, NASA would procure commercial transportation to ferry crews to the Moon and Mars in a similar way to how the agency buys rides for its astronauts to the International Space Station in low-Earth orbit.

NASA’s Curiosity rover captured images to create this selfie mosaic on the surface of Mars in 2015. If implemented as written, the Trump budget proposal would mark the first time in 30 years that NASA does not have a Mars lander in development. The agency would instead turn to commercial companies to demonstrate they can deliver payloads, and eventually humans, to the red planet.

The Trump administration’s statements on space policy have emphasized the longer-term goal of human missions to Mars. The White House’s plans for what NASA will do at the Moon after the Artemis program’s first landing are still undefined.

Petro has kept a low profile since becoming NASA’s temporary chief executive five months ago. If Trump moved forward with Isaacman’s nomination, he would likely be NASA administrator today. The Senate was a few days away from confirming Isaacman when Trump pulled his nomination, apparently for political reasons. The White House withdrew the nomination the day after Elon Musk, who backed Isaacman to take the top job at NASA, left the Trump administration.

Who’s running NASA?

Now, Petro could serve out the year as NASA’s acting administrator. Petro is well-regarded at Kennedy Space Center, where she was a fixture in the center’s headquarters building for nearly 20 years. But she lacks a political constituency in the Trump administration and isn’t empowered to make major policy decisions. The budget cuts proposed for NASA came from the White House’s Office of Management and Budget, not from within the agency itself.

President Trump has the reins on the process to select the next NASA administrator. Trump named Isaacman for the office in December, more than a month before his inauguration, and the earliest any incoming president has nominated a NASA administrator. Musk had close ties to Trump then, and a human mission to Mars got a mention in Trump’s inauguration speech.

But space issues seem to have fallen far down Trump’s list of priorities. Hughes, who got his job at NASA in part due to his political connections, suggested it might be a while before Trump gets around to selecting another NASA administrator nominee.

“I think the best guess would tell you that it’s hard to imagine it happening before the next six months, and could perhaps go longer than that into the eight- or nine-month range, but that’s purely speculation,” Hughes said, foreseeing impediments such as the large number of other pending nominations for posts across the federal government and high-priority negotiations with Congress over the federal budget.

Congress is also expected to go on recess in August, so the earliest a NASA nominee might get a confirmation hearing is this fall. Then, the Senate must vote to confirm the nominee before they can take office.

The timeline of Isaacman’s nomination for NASA administrator is instructive. Trump nominated Isaacman in December, and his confirmation hearing was in April. He was on the cusp of a confirmation vote in early June when Trump withdrew his nomination on May 31.

As NASA awaits a leader with political backing, Petro said the agency is undergoing an overhaul to make it “leaner and more agile.” This is likely to result in office closures, and Hughes indicated NASA might end up shuttering entire field centers.

“To the specific question, will they be closed or consolidated? I don’t think we’re there yet to answer that question, but it is actively a part of the conversation we’re having as we go step-by-step through this,” Hughes said.

What can $4 billion buy you?

While Trump’s budget proposal includes robust funding for human space exploration, it’s a different story for most of the rest of NASA. The agency’s science budget would be cut in half to approximately $3.9 billion. NASA’s technology development division would also be reduced by 50 percent.

If the White House gets its way, NASA would scale back research on the International Space Station and cancel numerous robotic missions in development or already in space. The agency would terminate missions currently exploring Jupiter, on the way to study an asteroid, and approaching interstellar space. It would shut down the largest X-ray space telescope ever built and the only one in its class likely to be operating for the next 10 years.

“There’s a lot of science that can still be done with $4 billion,” Petro said. “How we do science, and how we do partnerships, may change in the future to sort of multiply what we’re doing.”

These partnerships might include asking academic institutions or wealthy benefactors to pitch in money to fund science projects at NASA. The agency might also invite commercial companies to play bigger roles in NASA robotic missions, which are typically owned by the government.

This view of Jupiter’s turbulent atmosphere from NASA’s Juno spacecraft includes several of the planet’s southern jet streams. Juno is one of the missions currently in space that NASA would shut down under Trump’s budget request. Credit: NASA

One employee asked what NASA could do to secure more funding in the president’s budget request. But that ship has sailed. The options now available to NASA’s leadership are to support the budget proposal, stay silent, or leave. NASA is an executive agency and part of the Trump administration, and the White House’s budget request is NASA’s, too.

“It’s not our job to advocate, but let’s try to look at this in a positive way,” Petro said. “We’ve still got a lot of money. Let’s see how much mission we can do.”

Ultimately, it’s up to Congress to appropriate funding for NASA and other parts of the government. Lawmakers haven’t signaled where they might land on NASA’s budget, but Sen. Ted Cruz (R-Texas), who is influential on space-related matters, released the text of a proposed bill a few weeks ago that would restore funding for the International Space Station and forego cancellation of the Space Launch System rocket, among other things. But Cruz did not have much to say about adding more money for NASA’s science programs.

NASA’s senior leaders acknowledged on Wednesday that the pain of the agency’s downsizing will extend far beyond its walls.

“Eighty-five percent of our budget goes out the door to contractors,” Petro said. “So, with a reduced budget, absolutely, our contractors will also be impacted. In fact, they’re probably the bigger driver that will be impacted.”

It’s clearly a turbulent time for America’s space agency, and NASA employees have another month to decide if they want to be part of it.

“I know there’s a lot to consider,” Swails said. “There’s a lot that people are thinking about. I would encourage you to talk it out. Tap into your support systems. Talk to your spouse, your partner, your friend, your financial advisor, whomever you consider those trusted advisors for you.”

This sounds like hollow advice, but it seems like it’s all NASA’s workers can do. The Trump administration isn’t waiting for Congress to finalize the budget for 2026. The downsizing is here.

Photo of Stephen Clark

Stephen Clark is a space reporter at Ars Technica, covering private space companies and the world’s space agencies. Stephen writes about the nexus of technology, science, policy, and business on and off the planet.

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The axion may help clean up the messy business of dark matter

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We haven’t found evidence of the theoretical particle, but it’s still worth investigating.

In recent years, a curious hypothetical particle called the axion, invented to address challenging problems with the strong nuclear force, has emerged as a leading candidate to explain dark matter. Although the potential for axions to explain dark matter has been around for decades, cosmologists have only recently begun to seriously search for them. Not only might they be able to resolve some issues with older hypotheses about dark matter, but they also offer a dizzying array of promising avenues for finding them.

But before digging into what the axion could be and why it’s so useful, we have to explore why the vast majority of physicists, astronomers, and cosmologists accept the evidence that dark matter exists and that it’s some new kind of particle. While it’s easy to dismiss the dark matter hypothesis as some sort of modern-day epicycle, the reality is much more complex (to be fair to epicycles, it was an excellent idea that fit the data extremely well for many centuries).

The short version is that nothing in the Universe adds up.

We have many methods available to measure the mass of large objects like galaxies and clusters. We also have various methods to assess the effects of matter in the Universe, like the details of the cosmic microwave background or the evolution of the cosmic web. There are two broad categories: methods that rely solely on estimating the amount of light-emitting matter and methods that estimate the total amount of matter, whether it’s visible or not.

For example, if you take a picture of a generic galaxy, you’ll see that most of the light-emitting matter is concentrated in the core. But when you measure the rotation rate of the galaxy and use that to estimate the total amount of matter, you get a much larger number, plus some hints that it doesn’t perfectly overlap with the light-emitting stuff. The same thing happens for clusters of galaxies—the dynamics of galaxies within a cluster suggest the presence of much more matter than what we can see, and the two types of matter don’t always align. When we use gravitational lensing to measure a cluster’s contents, we again see evidence for much more matter than is plainly visible.

The tiny variations in the cosmic microwave background tell us about the influence of both matter that interacts with light and matter that doesn’t. It clearly shows that some invisible component dominated the early Universe. When we look at the large-scale structure, invisible matter rules the day. Matter that doesn’t interact with light can form structures much more quickly than matter that gets tangled up by interacting with itself. Without invisible matter, galaxies like the Milky Way can’t form quickly enough to match observations of the early Universe.

The calculations of Big Bang nucleosynthesis, which correctly predict the abundances of hydrogen and helium in the Universe, put strict constraints on how much light-emitting matter there can be, and that number simply isn’t large enough to accommodate all these disparate results.

Across cosmic scales in time and space, the evidence just piles up: There’s more stuff out there than meets the eye, and it can’t simply be dim-but-otherwise-regular matter.

Weakness of WIMPs

Since pioneering astronomer Vera Rubin first revealed dark matter in a big way in the 1970s, the astronomical community has tried every idea it could think of to explain these observations. One tantalizing possibility is that the dark matter is the entirely wrong approach; instead, we’re misunderstanding gravity itself. But so far, half a century later, all attempts to modify gravity ultimately fail one observational test or another. In fact, the most popular modified gravity theory, known as MOND, still requires the existence of dark matter, just less of it.

As the evidence piled up for dark matter in the 1980s and ’90s, astronomers began to favor a particular explanation known as WIMPs, for weakly interacting massive particles. WIMPs weren’t just made up on the spot. They were motivated by particle physics and our attempts to create theories beyond the Standard Model. Many extensions to the Standard Model predicted the existence of WIMP-like particles that could be made in abundance in the early Universe, generating a population of heavy-ish particles that remained largely in the cosmic background.

WIMPs seemed like a good idea, as they could both explain the dark matter problem and bring us to a new understanding of fundamental physics. The idea is that we are swimming in an invisible sea of dark matter particles that almost always simply pass through us undetected. But every once in a while, a WIMP should interact via the weak nuclear force (hence the origin of its name) and give off a shower of byproducts. One problem: We needed to detect one of these rare interactions. So experiments sprang up around the world to catch an elusive dark matter candidate.

With amazing names like CRESST, SNOLAB, and XENON, these experiments have spent years searching for a WIMP to no avail. They’re not an outright failure, though; instead, with every passing year, we know more and more about what the WIMP can’t be—what mass ranges and interaction strengths are now excluded.

By now, that list of what the WIMP can’t be is rather long, and large regions within the space of possibilities are now hard-and-fast ruled out.

OK, that’s fine. I mean, it’s a huge bummer that our first best guess didn’t pan out, but nature is under no obligation to make this easy for us. Maybe the dark matter isn’t a WIMP at all.

More entities are sitting around the particle physics attic that we might be able to use to explain this deep cosmic mystery. And one of those hypothetical particles is called the axion.

Cleaning up with axions

It was the late 1970s, and physicist Frank Wilczek was shopping for laundry detergent. He found one brand standing out among the bottles: Axion. He thought that would make an excellent name for a particle.

He was right.

For decades, physicists had been troubled by a little detail of the theory used to explain the strong nuclear force, known as quantum chromodynamics. By all measurements, that force obeys charge-parity symmetry, which means if you take an interaction, flip all the charges around, and run it in a mirror, you’ll get the same result. But quantum chromodynamics doesn’t enforce that symmetry on its own.

It seemed to be a rather fine-tuned state of affairs, with the strong force unnaturally maintaining a symmetry when there was nothing in the theory to explain why.

In 1977, Roberto Peccei and Helen Quinn discovered an elegant solution. By introducing a new field into the Universe, it could naturally introduce charge-parity symmetry into the equations of quantum chromodynamics. The next year, Wilczek and Gerard ‘t Hooft independently realized that this new field would imply the existence of a particle.

The axion.

Dark matter was just coming on the cosmic scene. Axions weren’t invented to solve that problem, but physicists very quickly realized that the complex physics of the early Universe could absolutely flood the cosmos with axions. What’s more, they would largely ignore regular matter and sit quietly in the background. In other words, the axion was an excellent dark matter candidate.

But axions were pushed aside as the WIMPs hypothesis gained more steam. Back-of-the-envelope calculations showed that the natural mass range of the WIMP would precisely match the abundances needed to explain the amount of dark matter in the Universe, with no other fine-tuning or adjustments required.

Never ones to let the cosmologists get in the way of a good time, the particle physics community kept up interest in the axion, finding different variations on the particle and devising clever experiments to see if the axion existed. One experiment requires nothing more than a gigantic magnet since, in an extremely strong magnetic field, axions can spontaneously convert into photons.

To date, no hard evidence for the axion has shown up. But WIMPs have proven to be elusive, so cosmologists are showing more love to the axion and identifying surprising ways that it might be found.

A sloshy Universe

Axions are tiny, even for subatomic particles. The lightest known particle is the neutrino, which weighs no more than 0.086 electron-volts (or eV). Compare that to, say, the electron, which weighs over half a million eV. The exact mass of the axion isn’t known, and there are many models and versions of the particle, but it can have a mass all the way down to a trillionth of an eV… and even lower.

In fact, axions belong to a much broader class of “ultra-light” dark matter particle candidates, which can have masses down to 10^-24 eV. This is multiple billions of times lighter than the WIMPs—and indeed most of the particles of the Standard Model.

That means axions and their friends act nothing like most of the particles of the Standard Model.

First off, it may not even be appropriate to refer to them as particles. They have such little mass that their de Broglie wavelength—the size of the quantum wave associated with every particle—can stretch into macroscopic proportions. In some cases, this wavelength can be a few meters across. In others, it’s comparable to a star or a solar system. In still others, a single axion “particle” can stretch across an entire galaxy.

In this view, the individual axion particles would be subsumed into a larger quantum wave, like an ocean of dark matter so large and vast that it doesn’t make sense to talk about its individual components.

And because axions are bosons, they can synchronize their quantum wave nature, becoming a distinct state of matter: a Bose-Einstein condensate. In a Bose-Einstein condensate, most of the particles share the same low-energy state. When this happens, the de Broglie wavelength is larger than the average separation between the particles, and the waves of the individual particles all add up together, creating, in essence, a super-particle.

This way, we may get axion “stars”—clumps of axions acting as a single particle. Some of these axion stars may be a few thousand kilometers across, wandering across interstellar space. Still others may be the size of galactic cores, which might explain an issue with the traditional WIMP picture.

The best description of dark matter in general is that it is “cold,” meaning that the individual particles do not move fast compared to the speed of light. This allows them to gravitationally interact and form the seeds of structures like galaxies and clusters. But this process is a bit too efficient. According to simulations, cold dark matter tends to form more small, sub-galactic clumps than we observe, and it tends to make the cores of galaxies much, much denser than we see.

Axions, and ultra-light dark matter in general, can provide a solution here because they would operate in two modes. At large scales, they can act like regular cold dark matter. But inside galaxies, they can condense, forming tight clumps. Critically, these clumps have uniform densities within them. This smooths out the distribution of axions within galaxies, preventing the formation of smaller clumps and ultra-dense cores.

A messy affair

Over the decades, astronomers and physicists have found an astounding variety of ways that axions might reveal their presence in the Universe. Because of their curious ability to transmute into photons in the presence of strong magnetic fields, any place that features strong fields—think neutron stars or even the solar corona—could produce extra radiation due to axions. That makes them excellent hunting grounds for the particles.

Axion stars—also sometimes known provocatively as dark stars—would be all but invisible under most circumstances. That is, until they destabilize in a cascading chain reaction of axion-to-photon conversion and blow themselves up.

Even the light from distant galaxies could betray the existence of axions. If they exist in a dense swarm surrounding a galaxy, their conversion to photons will contribute to the galaxy’s light, creating a signal that the James Webb Space Telescope can pick up.

To date, despite all these ideas, there hasn’t been a single shred of solid evidence for the existence of axions, which naturally drops them down a peg or two on the credibility scale. But that doesn’t mean that axions aren’t worth investigating further. The experiments conducted so far only place limits on what properties they might have; there’s still plenty of room for viable axion and axion-like candidates, unlike their WIMPy cousins.

There’s definitely something funny going on with the Universe. The dark matter hypothesis—that there is a large, invisible component to matter in the Universe—isn’t that great of an idea, but it’s the best one we have that fits the widest amount of available evidence. For a while, we thought we knew what the identity of that matter might be, and we spent decades (and small fortunes) in that search.

But while WIMPs were the mainstay hypothesis, that didn’t snuff out alternative paths. Dozens of researchers have investigated modified forms of gravity to equal levels of unsuccessfulness. And a small cadre has kept the axion flame alive. It’s a good thing, too, since their obscure explorations of the corners of particle physics laid the groundwork to flesh out axions into a viable competitor to WIMPs.

No, we haven’t found any axions. And we still don’t know what the dark matter is. But it’s only by pushing forward—advancing new ideas, testing them against the reality of observations, and when they fail, trying again—will we come to a new understanding. Axions may or may not be dark matter; the best we can say is that they are promising. But who wouldn’t want to live in a Universe filled with dark stars, invisible Bose-Einstein condensates, and strange new particles?

Photo of Paul Sutter

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