The orbiters that carried the radar hardware, along with one or two others, have been orbiting long enough that any major changes in Mars’ gravity caused by ice accumulation or crustal displacement would have shown up in their orbital behavior. The orbital changes they do see, “indicates that the increase in the gravitational potential associated with long-term ice accumulation is higher than the decrease in gravitational potential from downward deflection.” They calculate that the deformation has to be less than 0.13 millimeters per year to be consistent with the gravitational signal.
Finally, the model had to have realistic conditions at the polar ice cap, with a density consistent with a mixture of ice and dust.
Out of those 84 models, only three were consistent with all of these constraints. All three had a very viscous Martian interior, consistent with a relatively cold interior. That’s not a surprise, given what we’ve already inferred about Mars’ history. But it also suggests that most of the radioactive elements that provide heat to the red planet are in the crust, rather than deeper in the interior. That’s something we might have been able to check, had InSight’s temperature measurement experiment deployed correctly. But as it is, we’ll have to wait until some unidentified future mission to get a picture of Mars’ heat dynamics.
In any case, the models also suggest that Mars’ polar ice cap is less than 10 million years old, consistent with the orbitally driven climate models.
In a lot of ways, the new information is an update of earlier attempts to model the Martian interior, given a few more years of orbital data and the information gained from the InSight lander, which also determined the thickness of Mars’ crust and size of its core. But it’s also a good way of understanding how scientists can take bits and pieces of information from seemingly unrelated sources and build them into a coherent picture.
More data will likely reduce the chance of an impact to zero. If not, we have options.
Discovery images of asteroid 2024 YR4. Credit: ATLAS
Something in the sky captured the attention of astronomers in the final days of 2024. A telescope in Chile scanning the night sky detected a faint point of light, and it didn’t correspond to any of the thousands of known stars, comets, and asteroids in astronomers’ all-sky catalog.
The detection on December 27 came from one of a network of telescopes managed by the Asteroid Terrestrial-impact Last Alert System (ATLAS), a NASA-funded project to provide warning of asteroids on a collision course with Earth.
Within a few days, scientists gathered enough information on the asteroid—officially designated 2024 YR4—to determine that its orbit will bring it quite close to Earth in 2028, and then again in 2032. Astronomers ruled out any chance of an impact with Earth in 2028, but there’s a small chance the asteroid might hit our planet on December 22, 2032.
How small? The probability has fluctuated in recent days, but as of Thursday, NASA’s Center for Near Earth Object Studies estimated a 1.9 percent chance of an impact with Earth in 2032. The European Space Agency (ESA) put the probability at 1.8 percent. So as of now, NASA believes there’s a 1-in-53 chance of 2024 YR4 striking Earth. That’s about twice as likely as the lifetime risk of dying in a motor vehicle crash, according to the National Safety Council.
These numbers are slightly higher than the probabilities published last month, when ESA estimated a 1.2 percent chance of an impact. In a matter of weeks or months, the number will likely drop to zero.
No surprise here, according to ESA.
“It is important to remember that an asteroid’s impact probability often rises at first before quickly dropping to zero after additional observations,” ESA said in a press release. The agency released a short explainer video, embedded below, showing how an asteroid’s cone of uncertainty shrinks as scientists get a better idea of its trajectory.
Refining the risk
Scientists estimate that 2024 YR4 is between 130 to 300 feet (40 and 90 meters) wide, large enough to cause localized devastation near the impact site. The asteroid responsible for the Tunguska event of 1908, which leveled some 500 square miles (1,287 square kilometers) of forest in remote Siberia, was probably about the same size. The meteor that broke apart in the sky over Chelyabinsk, Russia, in 2013 was about 20 meters wide.
Astronomers use the Torino scale for measuring the risk of potential asteroid impacts. Asteroid 2024 YR4 is now rated at Level 3 on this scale, meaning it merits close attention from astronomers, the public, and government officials. This is the second time an asteroid has reached this level since the scale’s adoption in 1999. The other case happened in 2004, when asteroid Apophis briefly reached a Level 4 rating until further observations of the asteroid eliminated any chance of an impact with the Earth in 2029.
In the unlikely event that it impacts the Earth, an asteroid the size of 2024 YR4 could cause blast damage as far as 30 miles (50 kilometers) from the location of the impact or airburst if the object breaks apart in the atmosphere, according to the International Asteroid Warning Network (IAWN), established in the aftermath of the Chelyabinsk event.
The asteroid warning network is affiliated with the United Nations. Officials activate the IAWN when an asteroid bigger than 10 meters has a greater than 1 percent chance of striking Earth within the next 20 years. The risk of 2024 YR4 meets this threshold.
The red points on this image show the possible locations of asteroid 2024 YR4 on December 22, 2032, as projected by a Monte Carlo simulation. As this image shows, most of the simulations project the asteroid missing the Earth. Credit: ESA/Planetary Defense Office
Determining the asteroid’s exact size will be difficult. Scientists would need deep space radar observations, thermal infrared observations, or imagery from a spacecraft that could closely approach the asteroid, according to the IAWN. The asteroid won’t come close enough to Earth for deep space radar observations until shortly before its closest approach in 2032.
Astronomers need numerous observations to precisely plot an asteroid’s motion through the Solar System. Over time, these observations will reduce uncertainty and narrow the corridor the asteroid will follow as it comes near Earth.
Scientists already know a little about asteroid 2024 YR4’s orbit, which follows an elliptical path around the Sun. The orbit brings the asteroid inside of Earth’s orbit at its closest point to the Sun and then into the outer part of the asteroid belt when it is farthest from the Sun.
But there’s a complication in astronomers’ attempts to nail down the asteroid’s path. The object is currently moving away from Earth in almost a straight line. This makes it difficult to accurately determine its orbit by studying how its trajectory curves over time, according to ESA.
It also means observers will need to use larger telescopes to see the asteroid before it becomes too distant to see it from Earth in April. By the end of this year’s observing window, the asteroid warning network says the impact probability could increase to a couple tens of percent, or it could more likely drop back below the notification threshold (1 percent impact probability).
“It is possible that asteroid 2024 YR4 will fade from view before we are able to entirely rule out any chance of impact in 2032,” ESA said. “In this case, the asteroid will likely remain on ESA’s risk list until it becomes observable again in 2028.”
Planetary defenders
This means that public officials might need to start planning what to do later this year.
For the first time, an international board called the Space Mission Planning Advisory Group met this week to discuss what we can do to respond to the risk of an asteroid impact. This group, known as SMPAG, coordinates planning among representatives from the world’s space agencies, including NASA, ESA, China, and Russia.
The group decided on Monday to give astronomers a few more months to refine their estimates of the asteroid’s orbit before taking action. They will meet again in late April or early May or earlier if the impact risk increases significantly. If there’s still a greater than 1 percent probability of 2024 YR4 hitting the Earth, the group will issue a recommendation for further action to the United Nations Office for Outer Space Affairs.
So what are the options? If the data in a few months still shows that the asteroid poses a hazard to Earth, it will be time for the world’s space agencies to consider a deflection mission. NASA demonstrated its ability to alter the orbit of an asteroid in 2022 with a first-of-its-kind experiment in space. The mission, called DART, put a small spacecraft on a collision course with an asteroid two to four times larger than 2024 YR4.
The kinetic energy from the spacecraft’s death dive into the asteroid was enough to slightly nudge the object off its natural orbit around a nearby larger asteroid. This proved that an asteroid deflection mission could work if scientists have enough time to design and build it, an undertaking that took about five years for DART.
Italy’s LICIACube spacecraft snapped this image of asteroids Didymos (lower left) and Dimorphos (upper right) a few minutes after the impact of DART on September 26, 2022. Credit: ASI/NASA
A deflection mission is most effective well ahead of an asteroid’s potential encounter with the Earth, so it’s important not to wait until the last minute.
Fans of Hollywood movies know there’s a nuclear option for dealing with an asteroid coming toward us. The drawback of using a nuclear warhead is that it could shatter one large asteroid into many smaller objects, although recent research suggests a more distant nuclear explosion could produce enough X-ray radiation to push an asteroid off a collision course.
Waiting for additional observations in 2028 would leave little time to develop a deflection mission. Therefore, in the unlikely event that the risk of an impact rises over the next few months, it will be time for officials to start seriously considering the possibility of an intervention.
Even without a deflection, there’s plenty of time for government officials to do something here on Earth. It should be possible for authorities to evacuate any populations that might be affected by the asteroid.
The asteroid could devastate an area the size of a large city, but any impact is most likely to happen in a remote region or in the ocean. The risk corridor for 2024 YR4 extends from the eastern Pacific Ocean to northern South America, the Atlantic Ocean, Africa, the Arabian Sea, and South Asia.
There’s an old joke that dinosaurs went extinct because they didn’t have a space program. Whatever happens in 2032, we’re not at risk of extinction. However, occasions like this are exactly why most Americans think we should have a space program. A 2019 poll showed that 68 percent of Americans considered it very or extremely important for the space program to monitor asteroids, comets, or other objects from space that could strike the planet.
In contrast, about a quarter of those polled placed such importance on returning astronauts to the Moon or sending people to Mars. The cost of monitoring and deflecting asteroids is modest compared to the expensive undertakings of human missions to the Moon and Mars.
From taxpayers’ point of view, it seems this part of NASA offers the greatest bang for their buck.
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.
The huge area covered by these mounds gives a sense of just how significant this erosion was. “The dichotomy boundary has receded several hundred kilometres,” the researchers note. “Nearly all intervening material—approximately 57,000 cubic kilometers over an area of 284,000 square kilometers west of Ares Vallis alone—has been removed, leaving only remnant mounds.”
Based on the distribution of the different clays, the team argues that their water-driven formation took place before the erosion of the material. This would indicate that water-rock interactions were going on over a very wide region early in the history of Mars, which likely required an extensive hydrological cycle on the red planet. As the researchers note, a nearby ocean would have improved the chances of exposing this region to water, but the exposure could also have been due to processes like melting at the base of an ice cap.
Complicating matters further, many of the mounds top out below one proposed shoreline of the northern ocean and above a second. It’s possible that a receding ocean could have contributed to their erosion. But, at the same time, some of the features of a proposed shoreline now appear to have been caused by the general erosion of the original plateau, and may not be associated with an ocean at all.
Overall, the new results provide mixed evidence for the presence of a Martian ocean. They clearly show an active water cycle and erosion on a massive scale, which are both consistent with having a lot of water around. At the same time, however, the water exposure the mesas and buttes have experienced needn’t have come through their being submerged by said ocean and, given their elevation, might best be explained through some other process.
“We want to have the quickest, cheapest way to get these 30 samples back.”
This photo montage shows sample tubes shortly after they were deposited onto the surface by NASA’s Perseverance Mars rover in late 2022 and early 2023. Credit: NASA/JPL-Caltech/MSSS
For nearly four years, NASA’s Perseverance rover has journeyed across an unexplored patch of land on Mars—once home to an ancient river delta—and collected a slew of rock samples sealed inside cigar-sized titanium tubes.
These tubes might contain tantalizing clues about past life on Mars, but NASA’s ever-changing plans to bring them back to Earth are still unclear.
On Tuesday, NASA officials presented two options for retrieving and returning the samples gathered by the Perseverance rover. One alternative involves a conventional architecture reminiscent of past NASA Mars missions, relying on the “sky crane” landing system demonstrated on the agency’s two most recent Mars rovers. The other option would be to outsource the lander to the space industry.
NASA Administrator Bill Nelson left a final decision on a new mission architecture to the next NASA administrator working under the incoming Trump administration. President-elect Donald Trump nominated entrepreneur and commercial astronaut Jared Isaacman as the agency’s 15th administrator last month.
“This is going to be a function of the new administration in order to fund this,” said Nelson, a former Democratic senator from Florida who will step down from the top job at NASA on January 20.
The question now is: will they? And if the Trump administration moves forward with Mars Sample Return (MSR), what will it look like? Could it involve a human mission to Mars instead of a series of robotic spacecraft?
The Trump White House is expected to emphasize “results and speed” with NASA’s space programs, with the goal of accelerating a crew landing on the Moon and sending people to explore Mars.
NASA officials had an earlier plan to bring the Mars samples back to Earth, but the program slammed into a budgetary roadblock last year when an independent review team concluded the existing architecture would cost up to $11 billion—double the previous cost projection—and wouldn’t get the Mars specimens back to Earth until 2040.
This budget and schedule were non-starters for NASA. The agency tasked government labs, research institutions, and commercial companies to come up with better ideas to bring home the roughly 30 sealed sample tubes carried aboard the Perseverance rover. NASA deposited 10 sealed tubes on the surface of Mars a couple of years ago as insurance in case Perseverance dies before the arrival of a retrieval mission.
“We want to have the quickest, cheapest way to get these 30 samples back,” Nelson said.
How much for these rocks?
NASA officials said they believe a stripped-down concept proposed by the Jet Propulsion Laboratory in Southern California, which previously was in charge of the over-budget Mars Sample Return mission architecture, would cost between $6.6 billion and $7.7 billion, according to Nelson. JPL’s previous approach would have put a heavier lander onto the Martian surface, with small helicopter drones that could pick up sample tubes if there were problems with the Perseverance rover.
NASA previously deleted a “fetch rover” from the MSR architecture and instead will rely on Perseverance to hand off sample tubes to the retrieval lander.
An alternative approach would use a (presumably less expensive) commercial heavy lander, but this concept would still utilize several elements NASA would likely develop in a more traditional government-led manner: a nuclear power source, a robotic arm, a sample container, and a rocket to launch the samples off the surface of Mars and back into space. The cost range for this approach extends from $5.1 billion to $7.1 billion.
Artist’s illustration of SpaceX’s Starship approaching Mars. Credit: SpaceX
JPL will have a “key role” in both paths for MSR, said Nicky Fox, head of NASA’s science mission directorate. “To put it really bluntly, JPL is our Mars center in NASA science.”
If the Trump administration moves forward with either of the proposed MSR plans, this would be welcome news for JPL. The center, which is run by the California Institute of Technology under contract to NASA, laid off 955 employees and contractors last year, citing budget uncertainty, primarily due to the cloudy future of Mars Sample Return.
Without MSR, engineers at the Jet Propulsion Laboratory don’t have a flagship-class mission to build after the launch of NASA’s Europa Clipper spacecraft last year. The lab recently struggled with rising costs and delays with the previous iteration of MSR and NASA’s Psyche asteroid mission, and it’s not unwise to anticipate more cost overruns on a project as complex as a round-trip flight to Mars.
Ars submitted multiple requests to interview Laurie Leshin, JPL’s director, in recent months to discuss the lab’s future, but her staff declined.
Both MSR mission concepts outlined Tuesday would require multiple launches and an Earth return orbiter provided by the European Space Agency. These options would bring the Mars samples back to Earth as soon as 2035, but perhaps as late as 2039, Nelson said. The return orbiter and sample retrieval lander could launch as soon as 2030 and 2031, respectively.
“The main difference is in the landing mechanism,” Fox said.
To keep those launch schedules, Congress must immediately approve $300 million for Mars Sample Return in this year’s budget, Nelson said.
NASA officials didn’t identify any examples of a commercial heavy lander that could reach Mars, but the most obvious vehicle is SpaceX’s Starship. NASA already has a contract with SpaceX to develop a Starship vehicle that can land on the Moon, and SpaceX founder Elon Musk is aggressively pushing for a Mars mission with Starship as soon as possible.
NASA solicited eight studies from industry earlier this year. SpaceX, Blue Origin, Rocket Lab, and Lockheed Martin—each with their own lander concepts—were among the companies that won NASA study contracts. SpaceX and Blue Origin are well-capitalized with Musk and Amazon’s Jeff Bezos as owners, while Lockheed Martin is the only company to have built a lander that successfully reached Mars.
This slide from a November presentation to the Mars Exploration Program Analysis Group shows JPL’s proposed “sky crane” architecture for a Mars sample retrieval lander. The landing system would be modified to handle a load about 20 percent heavier than the sky crane used for the Curiosity and Perseverance rover landings. Credit: NASA/JPL
The science community has long identified a Mars Sample Return mission as the top priority for NASA’s planetary science program. In the National Academies’ most recent decadal survey released in 2022, a panel of researchers recommended NASA continue with the MSR program but stated the program’s cost should not undermine other planetary science missions.
Teeing up for cancellation?
That’s exactly what is happening. Budget pressures from the Mars Sample Return mission, coupled with funding cuts stemming from a bipartisan federal budget deal in 2023, have prompted NASA’s planetary science division to institute a moratorium on starting new missions.
“The decision about Mars Sample Return is not just one that affects Mars exploration,” said Curt Niebur, NASA’s lead scientist for planetary flight programs, in a question-and-answer session with solar system researchers Tuesday. “It’s going to affect planetary science and the planetary science division for the foreseeable future. So I think the entire science community should be very tuned in to this.”
Rocket Lab, which has been more open about its MSR architecture than other companies, has posted details of its sample return concept on its website. Fox declined to offer details on other commercial concepts for MSR, citing proprietary concerns.
“We can wait another year, or we can get started now,” Rocket Lab posted on X. “Our Mars Sample Return architecture will put Martian samples in the hands of scientists faster and more affordably. Less than $4 billion, with samples returned as early as 2031.”
Through its own internal development and acquisitions of other aerospace industry suppliers, Rocket Lab said it has provided components for all of NASA’s recent Mars missions. “We can deliver MSR mission success too,” the company said.
Rocket Lab’s concept for a Mars Sample Return mission. Credit: Rocket Lab
Although NASA’s deferral of a decision on MSR to the next administration might convey a lack of urgency, officials said the agency and potential commercial partners need time to assess what roles the industry might play in the MSR mission.
“They need to flesh out all of the possibilities of what’s required in the engineering for the commercial option,” Nelson said.
On the program’s current trajectory, Fox said NASA would be able to choose a new MSR architecture in mid-2026.
Waiting, rather than deciding on an MSR plan now, will also allow time for the next NASA administrator and the Trump White House to determine whether either option aligns with the administration’s goals for space exploration. In an interview with Ars last week, Nelson said he did not want to “put the new administration in a box” with any significant MSR decisions in the waning days of the Biden administration.
One source with experience in crafting and implementing US space policy told Ars that Nelson’s deferral on a decision will “tee up MSR for canceling.” Faced with a decision to spend billions of dollars on a robotic sample return or billions of dollars to go toward a human mission to Mars, the Trump administration will likely choose the latter, the source said.
If that happens, NASA science funding could be freed up for other pursuits in planetary science. The second priority identified in the most recent planetary decadal survey is an orbiter and atmospheric probe to explore Uranus and its icy moons. NASA has held off on the development of a Uranus mission to focus on the Mars Sample Return first.
Science and geopolitics
Whether it’s with robots or humans, there’s a strong case for bringing pristine Mars samples back to Earth. The titanium tubes carried by the Perseverance rover contain rock cores, loose soil, and air samples from the Martian atmosphere.
“Bringing them back will revolutionize our understanding of the planet Mars and indeed, our place in the solar system,” Fox said. “We explore Mars as part of our ongoing efforts to safely send humans to explore farther and farther into the solar system, while also … getting to the bottom of whether Mars once supported ancient life and shedding light on the early solar system.”
Researchers can perform more detailed examinations of Mars specimens in sophisticated laboratories on Earth than possible with the miniature instruments delivered to the red planet on a spacecraft. Analyzing samples in a terrestrial lab might reveal biosignatures, or the traces of ancient life, that elude detection with instruments on Mars.
“The samples that we have taken by Perseverance actually predate—they are older than any of the samples or rocks that we could take here on Earth,” Fox said. “So it allows us to kind of investigate what the early solar system was like before life began here on Earth, which is amazing.”
Fox said returning Mars samples before a human expedition would help NASA prioritize where astronauts should land on the red planet.
In a statement, the Planetary Society said it is “concerned that NASA is again delaying a decision on the program, committing only to additional concept studies.”
“It has been more than two years since NASA paused work on MSR,” the Planetary Society said. “It is time to commit to a path forward to ensure the return of the samples already being collected by the Perseverance rover.
“We urge the incoming Trump administration to expedite a decision on a path forward for this ambitious project, and for Congress to provide the funding necessary to ensure the return of these priceless samples from the Martian surface.”
China says it is developing its own mission to bring Mars rocks back to Earth. Named Tianwen-3, the mission could launch as soon as 2028 and return samples to Earth by 2031. While NASA’s plan would bring back carefully curated samples from an expansive environment that may have once harbored life, China’s mission will scoop up rocks and soil near its landing site.
“They’re just going to have a mission to grab and go—go to a landing site of their choosing, grab a sample and go,” Nelson said. “That does not give you a comprehensive look for the scientific community. So you cannot compare the two missions. Now, will people say that there’s a race? Of course, people will say that, but it’s two totally different missions.”
Still, Nelson said he wants NASA to be first. He said he has not had detailed conversations with Trump’s NASA transition team.
“I think it was a responsible thing to do, not to hand the new administration just one alternative if they want to have a Mars Sample Return,” Nelson said. “I can’t imagine that they don’t. I don’t think we want the only sample return coming back on a Chinese spacecraft.”
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.
Notably, the Dragonfly launch was one of the first times United Launch Alliance has been eligible to bid its new Vulcan rocket for a NASA launch contract. NASA officials gave the green light for the Vulcan rocket to compete head-to-head with SpaceX’s Falcon 9 and Falcon Heavy after ULA’s new launcher had a successful debut launch earlier this year. With this competition, SpaceX came out on top.
A half-life of 88 years
NASA’s policy for new space missions is to use solar power whenever possible. For example, Europa Clipper was originally supposed to use a nuclear power generator, but engineers devised a way for the spacecraft to use expansive solar panels to capture enough sunlight to produce electricity, even at Jupiter’s vast distance from the Sun.
But there are some missions where this isn’t feasible. One of these is Dragonfly, which will soar through the soupy nitrogen-methane atmosphere of Titan. Saturn’s largest moon is shrouded in cloud cover, and Titan is nearly 10 times farther from the Sun than Earth, so its surface is comparatively dim.
The Dragonfly mission, seen here in an artist’s concept, is slated to launch no earlier than 2027 on a mission to explore Saturn’s moon Titan. Credit: NASA/JHUAPL/Steve Gribben
Dragonfly will launch with about 10.6 pounds (4.8 kilograms) of plutonium-238 to fuel its power generator. Plutonium-238 has a half-life of 88 years. With no moving parts, RTGs have proven quite reliable, powering spacecraft for many decades. NASA’s twin Voyager probes are approaching 50 years since launch.
The Dragonfly rotorcraft will launch cocooned inside a transit module and entry capsule, then descend under parachute through Titan’s atmosphere, which is four times denser than Earth’s. Finally, Dragonfly will detach from its descent module and activate its eight rotors to reach a safe landing.
Once on Titan, Dragonfly is designed to hop from place to place on numerous flights, exploring environments rich in organic molecules, the building blocks of life. This is one of NASA’s most exciting, and daring, robotic missions of all time.
After launching from NASA’s Kennedy Space Center in Florida in July 2028, it will take Dragonfly about six years to reach Titan. When NASA selected the Dragonfly mission to begin development in 2019, the agency hoped to launch the mission in 2026. NASA later directed Dragonfly managers to target a launch in 2027, and then 2028, requiring the mission to change from a medium-lift to a heavy-lift rocket.
Dragonfly has also faced rising costs NASA blames on the COVID-19 pandemic and supply chain issues and an in-depth redesign since the mission’s selection in 2019. Collectively, these issues caused Dragonfly’s total budget to grow to $3.35 billion, more than double its initial projected cost.
Our Solar System’s Kuiper Belt appears to be substantially larger than we thought.
Back in 2017, NASA graphics indicated that New Horizons would be at the outer edge of the Kuiper Belt by around 2020. That hasn’t turned out to be true. Credit: NASA
Back in 2017, NASA graphics indicated that New Horizons would be at the outer edge of the Kuiper Belt by around 2020. That hasn’t turned out to be true. Credit: NASA
In the outer reaches of the Solar System, beyond the ice giant Neptune, lies a ring of comets and dwarf planets known as the Kuiper Belt. The closest of these objects are billions of kilometers away. There is, however, an outer limit to the Kuiper Belt. Right?
Until now, it was thought there was nothing beyond 48 AU (astronomical units) from the Sun, (one AU is slightly over 150 million km). It seemed there was little beyond that. That changed when NASA’s New Horizons team detected 11 new objects lurking from 60 to 80 AU. What was thought to be empty space turned out to be a gap between the first ring of Kuiper Belt objects and a new, second ring. Until now, it was thought that our Solar System is unusually small when compared to exosolar systems, but it evidently extends farther out than anyone imagined.
While these objects are only currently visible as pinpoints of light, and Fraser is allowing room for error until the spacecraft gets closer, what their existence could tell us about the Kuiper Belt and the possible origins of the Solar System is remarkable.
Living on the edge
The extreme distance of the new objects has put them in a class all their own. Whether they are similar to other Kuiper Belt objects in morphology and composition remains unknown since they are so faint. As New Horizons approaches them, observations are now simultaneously being made with its LORRI (Long Range Reconnaissance Imager) telescope and the Subaru Telescope, which might reveal that they actually do not belong to a different class in terms of composition.
“The reason we’re using Subaru is its Hyper Suprime-Cam, which has a really wide field of vision,” New Horizons researcher Wesley Fraser, who led the study, told Ars Technica (the results are soon to be published in the Planetary Science Journal). “The camera can go deep and wide quickly, and we stare down the pipe of LORRI, looking down that trajectory to find anything nearby.”
These objects are near the edge of the heliosphere of the Solar System, where it transitions to interstellar space. The heliosphere is formed by the outflow of charged particles, or solar wind, that creates something of a bubble around our Solar System; combined with the Sun’s magnetic field, this protects us from outside cosmic radiation.
The new objects are located where the strength of the Sun’s magnetic field starts to break down. They might even be far enough for their orbits to occasionally take them beyond the heliosphere, where they will be pummeled by intense cosmic radiation from the interstellar medium. This, combined with their solar wind exposure, might affect their composition, making it different from that of closer Kuiper Belt objects.
Even though it is impossible to know what these objects are like up close for now, how can we think of them? Fraser has an idea.
“If I had to guess, they are probably red and dark and devoid of water ice on the surface, which is quite common in the Kuiper Belt,” he said. “I think these objects will look a lot like the dwarf planet Sedna, but it’s possible they will look even more unusual.”
Many Kuiper Belt objects are a deep reddish color as a result of their organic chemicals being exposed to cosmic radiation. This breaks the hydrogen bonds in those chemicals, releasing much of the hydrogen into space and leaving behind an amorphous organic sludge that keeps getting redder the longer it is irradiated.
Fraser also predicts these objects are lacking in surface water ice because more distant Kuiper Belt objects (though not nearly as far-flung as the newly discovered ones) have not shown signs of it in observations. While water ice is common in the Kuiper Belt, he thinks these objects are probably hiding water ice underneath their red exterior.
Emerging from the dark
Investigating objects like this could change views on the origins of the Solar System and how it compares to the exosolar systems we have observed. Is our Solar System even normal?
Because the Kuiper Belt was thought to end at a distance of about 48 AU, the Solar System used to seem small compared to exosolar systems, where there are still objects floating around 150 AU from their star. The detection of objects at up to 80 AU from the Sun has put the Solar System in more of a normal range. It also seems to suggest that, since it is larger than we thought, that it also formed in a larger nebula.
“The timeline for Solar System formation is what we have to work out, and looking at the Kuiper Belt sets the stage for that very earliest moment, when gas and dust start to coalesce into macroscopic objects,” said New Horizons researcher Marc Buie. Buie discovered the object Arrokoth and led another study recently published in The Planetary Science Journal.
Arrokoth itself altered ideas about planet formation since its two lobes appear to have gently stuck together instead of crashing into each other in a violent collision, as some of our ideas had assumed. Nothing like it has ever been observed before or since.
Dust to dust
There is another potential thing that the New Horizons team is watching out for, and that is whether the new objects are binary.
About 10 to 15 percent of all known Kuiper Belt objects orbit partners in binary systems, and Fraser thinks binarity can reveal many things about the formation of planetesimals, solid objects that form in a young star system through gentle mergers with other objects that cause them to stick together. Some of these objects can become gravitationally bound to each other and form binaries.
As New Horizons travels farther, its dust counter, which sends back information about the velocity and mass of dust that hits it, shows that the amount of dust in its surroundings has not gone down. This dust comes from objects running into each other.
“It’s been finding that, as we go farther and farther out, the Solar System is getting dustier and dustier, which is exactly the opposite of what is expected at that distance,” New Horizons Principal Investigator Alan Stern told Ars Technica. “There might be a massive population of bodies colliding out there.”
NASA had previously decided that it was unlikely New Horizons would be able to pull off another Kuiper Belt object flyby like it did with Arrokoth, so the mission’s focus shifted to the heliosphere. Now that the New Horizons team has found unexpected objects this distant with the help of the Subaru Telescope, and dust keeps being detected as the spacecraft travels farther out, there might be an opportunity for another flyby. Stern is still cautious about the chances of that.
“We’re going to see how they compare to closer Kuiper Belt objects, but if we can find one we can get close to, we’ll get a chance to really compare their geology and their mode of origin,” Stern said. “But that’s a longshot because we’re running on a tenth of a tank of gas.”
The advantage of using Subaru combined with LORRI is that LORRI can be pointed sideways to see objects, or at least slightly past them, at right angles. This will be the dream team of telescopes if New Horizons can approach at least one of the new objects. If an object is behind the spacecraft, combining observations from different angles gives information about the physical surface of an object.
Using the Nancy Grace Roman Telescope could yield even more surprising observations in the future. It has a smaller mirror and a very wide field of view, Stern likens it to space binoculars, and it only has to be pointed at a target region once or twice (in comparison to hundreds of times for the James Webb Space Telescope) to search for and possibly discover objects in an extremely vast expanse of sky. Most other telescopes would have to be pointed thousands of times to do that.
“The desperate hope for all of us is that we will find more flyby targets,” Buie said. “If we could just get an object to register as a couple of pixels on LORRI, that would be incredible.”
Just a note to you on some stuff that’s going on in the background here. About a year ago, NASA decided that another KBO flyby was really unlikely, so they switched the mission focus to heliophysics (i.e., the edge of the heliosphere). Stern tried to fight that, and he has really looked to keep the focus on KBOs, which NASA now considers a “if we find one it can image, it will” situation. So I think a lot of his phrasing is in keeping with what he wants—more flybys. But it’s our job to give an accurate picture, which is that this event is unlikely.
Elizabeth Rayne is a creature who writes. Her work has appeared on SYFY WIRE, Space.com, Live Science, Grunge, Den of Geek, and Forbidden Futures. She lurks right outside New York City with her parrot, Lestat. When not writing, she is either shapeshifting, drawing, or cosplaying as a character nobody has ever heard of. Follow her on Threads and Instagram @quothravenrayne.
Enlarge/ Sandia National Labs’ Z machine in action.
The old joke about the dinosaurs going extinct because they didn’t have a space program may be overselling the need for one. It turns out you can probably divert some of the more threatening asteroids with nothing more than the products of a nuclear weapons program. But it doesn’t work the way you probably think it does.
Obviously, nuclear weapons are great at destroying things, so why not asteroids? That won’t work because a lot of the damage that nukes generate comes from the blast wave as it propagates through the atmosphere. And the environment around asteroids is notably short on atmosphere, so blast waves won’t happen. But you can still use a nuclear weapon’s radiation to vaporize part of the asteroid’s surface, creating a very temporary, very hot atmosphere on one side of the asteroid. This should create enough pressure to deflect the asteroid’s orbit, potentially causing it to fly safely past Earth.
But will it work? Some scientists at Sandia National Lab have decided to tackle a very cool question with one of the cooler bits of hardware on Earth: the Z machine, which can create a pulse of X-rays bright enough to vaporize rock. They estimate that a nuclear weapon can probably impart enough force to deflect asteroids as large as 4 kilometers across.
No nukes! (Just a nuclear simulation)
The Z machine is at the heart of Sandia’s Z Pulsed Power Facility. It’s basically a mechanism for storing a whole lot of electrical energy—up to 22 megajoules—and releasing it nearly instantaneously. Anything in the immediate vicinity experiences extremely intense electromagnetic fields. Among other things, this can be used to heavily ionize materials, like the argon gas used here, generating intense X-rays. These served as a stand-in for the radiation generated by a nuclear weapon.
For an asteroid, the researcher used disks of rock, either quartz or fused silica. (Notably, they only did one sample of each but got reasonably consistent results from them.) Mere mortals might have stuck the disk on a device that could register the force it experienced and left it at that. But these scientists were made of sterner stuff and decided that this wouldn’t really replicate the asteroid experience of floating freely in space.
To mimic that, the researchers held the rock disks in place using thin pieces of foil. These would vaporize almost instantly as the X-ray burst arrives, leaving the rock briefly suspended in the air. While gravity would have its way, the events triggered by the radiation evaporating away a bunch of the rock would be over before the sample experienced any significant downward acceleration. Its movement during this time, and thus the force imparted to it by the evaporation of its surface, was tracked by a laser interferometer placed on the far side of the disk from the X-ray source.
With all that set, all that was left was to fire up the Z machine and vaporize some rock.
Enlarge/ A “selfie” photo of China’s Zhurong rover and the Tianwen-1 landing platform on Mars in 2021.
China plans to launch two heavy-lift Long March 5 rockets with elements of the Tianwen-3 Mars sample return mission in 2028, the mission’s chief designer said Thursday.
In a presentation at a Chinese space exploration conference, the chief designer of China’s robotic Mars sample return project described the mission’s high-level design and outlined how the mission will collect samples from the Martian surface. Reports from the talk published on Chinese social media and by state-run news agencies were short on technical details and did not discuss any of the preparations for the mission.
Public pronouncements by Chinese officials on future space missions typically come true, but China is embarking on challenging efforts to explore the Moon and Mars. China aims to land astronauts on the lunar surface by 2030 in a step toward eventually building a Moon base called the International Lunar Research Station.
Liu Jizhong, chief designer of the Tianwen-3 mission, did not say when China could have Mars samples back on Earth. In past updates on the Tianwen-3 mission, the launch date has alternated between 2028 and 2030, and officials previously suggested the round-trip mission would take about three years. This would suggest Mars rocks could return to Earth around 2031, assuming an on-time launch in 2028.
NASA, meanwhile, is in the middle of revamping its architecture for a Mars sample return mission in cooperation with the European Space Agency. In June, NASA tapped seven companies, including SpaceX and Blue Origin, to study ways to return Mars rocks to Earth for less than $11 billion and before 2040, the cost and schedule for NASA’s existing plan for Mars sample return.
That is too expensive and too long to wait for Mars sample return, NASA Administrator Bill Nelson said in April. Mars sample return is the highest priority for NASA’s planetary science division and has been the subject of planning for decades. The Perseverance rover currently on Mars is gathering several dozen specimens of rock powder, soil, and Martian air in cigar-shaped titanium tubes for eventual return to Earth.
This means China has a shot at becoming the first country to bring pristine samples from Mars back to Earth, and China doesn’t intend to stop there.
“If all the missions go as planned, China is likely to become the first country to return samples from Mars,” said Wu Weiren, chief designer of China’s lunar exploration program, in a July interview with Chinese state television. “And we will explore giant planets, such as Jupiter. We will also explore some of the asteroids, including sample return missions from an asteroid, and build an asteroid defense system.”
The asteroid sample return mission is known as Tianwen-2, and is scheduled for launch next year. Tianwen means “questions to heaven.”
China doesn’t have a mission currently on Mars gathering material for its Tianwen-3 sample return mission. The country’s first Mars mission, Tianwen-1, landed on the red planet in May 2021 and deployed a rover named Zhurong. China’s space agency hasn’t released any update on the rover since 2022, suggesting it may have succumbed to the harsh Martian winter.
So, the Tianwen-3 mission must carry everything it needs to land on Mars, collect samples, package them for return to Earth, and then launch them from the Martian surface back into space. Then, the sample carrier will rendezvous with a return vehicle in orbit around Mars. Once the return spacecraft has the samples, it will break out of Mars orbit, fly across the Solar System, and release a reentry capsule to bring the Mars specimens to the Earth.
All of the kit for the Tianwen-3 mission will launch on two Long March 5 rockets, the most powerful operational launcher in China’s fleet. One Long March 5 will launch the lander and ascent vehicle, and another will propel the return spacecraft and Earth reentry capsule toward Mars.
Liu, Tianwen-3’s chief designer, said an attempt to retrieve samples from Mars is the most technically challenging space exploration mission since the Apollo program, according to China’s state-run Xinhua news agency. Liu said China will adhere to international agreements on planetary protection to safeguard Mars, Earth, and the samples themselves from contamination. The top scientific goal of the Tianwen-3 mission is to search for signs of life, he said.
Tianwen-3 will collect samples with a robotic arm and a subsurface drill, and Chinese officials previously said the mission may carry a helicopter and a mobile robot to capture more diverse Martian materials farther away from the stationary lander.
Liu said China is open to putting international payloads on Tianwen-3 and will collaborate with international scientists to analyze the Martian samples the mission returns to Earth. China is making lunar samples returned by the Chang’e 5 mission available for analysis by international researchers, and Chinese officials have said they anticipate a similar process to loan out samples from the far side of the Moon brought home by the Chang’e 6 mission earlier this year.
Enlarge/ The eruptions that produced the dark mare on the lunar surface ended billions of years ago.
Signs of volcanic activity on the Moon can be viewed simply by looking up at the night-time sky: The large, dark plains called “maria” are the product of massive outbursts of volcanic material. But these were put in place relatively early in the Moon’s history, with their formation ending roughly 3 billion years ago. Smaller-scale additions may have continued until roughly 2 billion years ago. Evidence of that activity includes samples obtained by China’s Chang’e-5 lander.
But there are hints that small-scale volcanism continued until much more recent times. Observations from space have identified terrain that seems to be the product of eruptions, but only has a limited number of craters, suggesting a relatively young age. But there’s considerable uncertainty about these deposits.
Now, further data from samples returned to Earth by the Chang’e-5 mission show clear evidence of volcanism that is truly recent in the context of the history of the Solar System. Small beads that formed during an eruption have been dated to just 125 million years ago.
Counting beads
Obviously, some of the samples returned by Chang’e-5 are solid rock. But it also returned a lot of loose material from the lunar regolith. And that includes a decent number of rounded, glassy beads formed from molten material. There are two potential sources of those beads: volcanic activity and impacts.
The Moon is constantly bombarded by particles ranging in size from individual atoms to small rocks, and many of these arrive with enough energy to melt whatever it is they smash into. Some of that molten material will form these beads, which may then be scattered widely by further impacts. The composition of these beads can vary wildly, as they’re composed of either whatever smashed into the Moon or whatever was on the Moon that got smashed. So, the relative concentrations of different materials will be all over the map.
By contrast, any relatively recent volcanism on the Moon will be extremely rare, so is likely to be from a single site and have a single composition. And, conveniently, the Apollo missions already returned samples of volcanic lunar rocks, which provide a model for what that composition might look like. So, the challenge was one of sorting through the beads returned from the Chang’e-5 landing site, and figuring out which ones looked volcanic.
And it really was a challenge, as there were over 3,000 beads returned, and the vast majority of them would have originated in impacts.
As a first cutoff, the team behind the new work got rid of anything that had a mixed composition, such as unmelted material embedded in the bead, or obvious compositional variation. This took the 3,000 beads down to 764. Those remaining beads were then subject to a technique that could determine what chemicals were present. (The team used an electron probe microanalyzer, which bombards the sample with electrons and uses the photons that are emitted to determine what elements are present.) As expected, compositions were all over the map. Some beads were less than 1 percent magnesium oxide; others nearly 30 percent. Silicon dioxide ranged from 16 to 60 percent.
Based on the Apollo samples, the researchers selected for beads that were high in magnesium oxide relative to calcium and aluminum oxides. That got them down to 13 potentially volcanic samples. They also looked for low nickel, as that’s found in many impactors, which got the number down to six. The final step was to look at sulfur isotopes, as impact melting tends to preferentially release the lighter isotope, altering the ratio compared to intact lunar rocks.
After all that, the researchers were left with three of the glassy beads, which is a big step down from the 3,000 they started with.
Erupted
Those three were then used to perform uranium-based radioactive dating, and they all produced numbers that were relatively close to each other. Based on the overlapping uncertainties, the researchers conclude that all were the product of an eruption that took place about 123 million years ago, give or take 15 million years. Considering that the most recent confirmed eruptions were about 2 billion years ago, that’s a major step forward in timing.
And that’s quite a bit of a surprise, as the Moon has had plenty of time to cool, and that cooling would have increased the distance between its surface and any molten material left in the interior. So it’s not obvious what could be creating sufficient heating to generate molten material at present. The researchers note that the Moon has a lot of material called KREEP (potassium, rare earth elements, phosphorus) that is high in radioactive isotopes and might lead to localized heating in some circumstances.
Unfortunately, it will be tough to associate this with any local geology, since there’s no indication of where the eruption occurred. Material this small can travel quite a distance in the Moon’s weak gravitational field and then could be scattered even farther by impacts. So, it’s possible that these belong to features that have been identified as potentially volcanic through orbital images.
In the meantime, the increased exploration of the Moon planned for the next few decades should get us more opportunities to see whether similar materials are widespread on the lunar surface. Eventually, that might potentially allow us to identify an area with higher concentrations of volcanic material than one particle in a thousand.
Enlarge/ Artist’s rendition of the LADEE mission above the lunar surface.
The Moon may not have much of an atmosphere, mostly because of its weak gravitational field (whether it had a substantial atmosphere billions of years ago is debatable). But it is thought to presently be maintaining its tenuous atmosphere—also known as an exosphere—because of meteorite impacts.
Space rocks have been bombarding the Moon for its 4.5-billion-year existence. Researchers from MIT and the University of Chicago have now found that lunar soil samples collected by astronauts during the Apollo era show evidence that meteorites, from hulking meteors to micrometeoroids no bigger than specks of dust, have launched a steady flow of atoms into the exosphere.
Though some of these atoms escape into space and others fall back to the surface, those that do remain above the Moon create a thin atmosphere that keeps being replenished as more meteorites crash into the surface.
“Over long timescales, micrometeorite impact vaporization is the primary source of atoms in the lunar atmosphere,” the researchers said in a study recently published in Science Advances.
Ready for launch
When NASA sent its orbiter LADEE (Lunar Atmosphere and Dust Environment Explorer) to the Moon in 2013, the mission was intended to find out the origins of the Moon’s atmosphere. LADEE observed more atoms in the atmosphere during meteor showers, which suggested impacts had something to do with the atmosphere. However, it left questions about the mechanism that converts impact energy into a diffuse atmosphere.
To find these answers, a team of MIT and University of Chicago researchers, led by professor Nicole Nie of MIT’s Department of Earth, Atmospheric and Planetary Sciences, needed to analyze the isotopes of elements in lunar soil that are most susceptible to the effects of micrometeoroid impacts. They chose potassium and rubidium.
Potassium and rubidium ions are especially prone to two processes: impact vaporization and ion sputtering.
Impact vaporization results from particles colliding at high speeds and generating extreme amounts of heat that excite atoms enough to vaporize the material they are in and send them flying. Ion sputtering involves high-energy impacts that set atoms free without vaporization. Atoms that are released by ion sputtering tend to have more energy and move faster than those released by impact vaporization.
Either of these can create and maintain the lunar atmosphere in the wake of meteorite impacts.
So, if atoms sent into the atmosphere by ion sputtering have an energy advantage, then why did the researchers find that most atoms in the atmosphere actually come from impact vaporization?
Touching back down
Since the lunar soil samples provided by NASA had previously had their lighter and heavier isotopes of potassium and rubidium quantified, Lie’s team used calculations to determine which collision process is more likely to keep different isotopes from fleeing the atmosphere.
The researchers found that atoms transferred to the atmosphere by ion sputtering are sent zooming at such high energies that they often reach escape velocity—the minimum velocity needed to escape the Moon’s already feeble gravity—and continue to travel out into space. Atoms that end up in the atmosphere can also be lost from the atmosphere, after all.
The fraction of atoms that reach escape velocity after impact vaporization depends on the temperature of those atoms. Lower energy levels associated with impact vaporization result in lower temperatures, which give atoms a lower chance of escape.
“Impact vaporization is the dominant long-term source of the lunar atmosphere, likely contributing more than 65 percent of atmospheric [potassium] atoms, with ion sputtering accounting for the rest,” Lie and her team said in the same study.
There are other ways atoms are lost from the lunar atmosphere. It is mostly lighter ions that tend to stick around in the exosphere, with ions falling back to the surface if they’re too heavy. Others are photoionized by electromagnetic radiation from the solar wind and often carried off into space by solar wind particles.
What we’ve learned about the lunar atmosphere through lunar soil could influence studies of other bodies. Impact vaporization has already been found to launch atoms into the exosphere of Mercury, which is thinner than the Moon’s. Studying Martian soil, which may land on Earth with sample return missions in the future, could also give more insight into how meteorite impacts affect its atmosphere.
As we approach a new era of manned lunar missions, the Moon may have more to tell us about where its atmosphere comes from—and where it goes.
Enlarge/ Image of Epsilon Indi A at two wavelengths, with the position of its host star indicated by an asterisk.
T. Müller (MPIA/HdA), E. Matthews (MPIA)
We have a couple of techniques that allow us to infer the presence of an exoplanet based on its effects on the light coming from its host star. But there’s an alternative approach that sometimes works: image them directly. It’s much more limited, since the planet has to be pretty big and orbiting far away enough from its star to avoid having light coming from the planet swamped by the far more intense starlight.
Still, it has been done. Massive exoplanets have been captured relatively shortly after their formation, when the heat generated by the collapse of material into the planet causes them to glow in the infrared. But the Webb telescope is far more sensitive than any infrared observatory we’ve ever built, and it has managed to image a relatively nearby exoplanet that’s roughly as old as the ones in our Solar System.
Looking directly at a planet
What do you need to directly image a planet that’s orbiting a star light-years away? The first thing is a bit of hardware called a coronagraph attached to your telescope. This is responsible for blocking the light from the star the planet is orbiting; without it, that light will swamp any other sources in the exosolar system. Even with a good coronagraph, you need the planets to be orbiting at a significant distance from the star so that they’re cleanly separated from the signal being blocked by the coronagraph.
Then, you need the planet to emit a fair bit of light. While the right surface composition might allow the planet to be highly reflective, that’s not going to be a great option considering the distances we’d need the planet to be orbiting to be visible at all. Instead, the planets we’ve spotted so far have been young and still heated by the processes that brought material together to form a planet in the first place. Being really big doesn’t hurt matters either.
Put that all together, and what you expect to be able to spot is a very young, very distant planet that’s massive enough to fall into the super-Jupiter category.
But the launch of the Webb Space Telescope has given us new capabilities in the infrared range, and a large international team of researchers pointed it at a star called Epsilon Indi A. It’s a bit less than a dozen light years away (which is extremely close in astronomical terms), and the star is both similar in size and age to the Sun, making it an interesting target for observations. Perhaps most significantly previous data had suggested a large exoplanet would be found, based on indications that the star was apparently shifting as the exoplanet tugged on it during its orbit.
And there was in fact an indication of a planet there. It just didn’t look much like the expected planet. “It’s about twice as massive, a little farther from its star, and has a different orbit than we expected,” said Elisabeth Matthews, one of the researchers involved.
At the moment, there’s no explanation for the discrepancy. The odds of it being an unrelated background object are extremely small. And a reanalysis of data on the motion of Epsilon Indi A suggests that this is likely to be the only large planet in the system—there could be additional planets, but they’d be much smaller. So, the researchers named the planet Epsilon Indi Ab, even though that was the same name given to the planet that doesn’t seem to match this one’s properties.
Big, cold, and a bit enigmatic
The revised Epsilon Indi Ab is a large planet, estimated at roughly six times the mass of Jupiter. It’s also orbiting at roughly the same distance as Neptune. It’s generally bright across the mid-infrared, consistent with a planet that’s roughly 275 Kelvin—not too far off from room temperature. That’s also close to what we would estimate for its temperature simply based on the age of the planet. That makes it the coolest exoplanet ever directly imaged.
While the signal from the planet was quite bright at a number of wavelengths, the planet couldn’t even be detected in one area of the spectrum (3.5 to 5 micrometers, for the curious). That’s considered an indication that the planet has high levels of elements heavier than helium, and a high ratio of carbon to oxygen. The gap in the spectrum may influence estimates of the planet’s age, so further observations will probably need to be conducted to clarify why there are no emissions at these wavelengths.
The researchers also suggest that imaging more of these cool exoplanets should be a priority, given that we should be cautious about extrapolating anything from a single example. So, in that sense, this first exoplanet imaging provides an important confirmation that, with Webb and its coronagraph, we’ve now got the tools we need to do so, and they work very well.
Enlarge/ Renditions of a possible composition of LHS 1140 b, with a patch of ocean on the side facing its host star. Earth is included at right for scale.
Of all the potential super-Earths—terrestrial exoplanets more massive than Earth—out there, an exoplanet orbiting a star only 40 light-years away from us in the constellation Cetus might be the most similar to have been found so far.
Exoplanet LHS 1140 b was assumed to be a mini-Neptune when it was first discovered by NASA’s James Webb Space Telescope toward the end of 2023. After analyzing data from those observations, a team of researchers, led by astronomer Charles Cadieux, of Université de Montréal, suggest that LHS 1140 b is more likely to be a super-Earth.
If this planet is an alternate version of our own, its relative proximity to its cool red dwarf star means it would most likely be a gargantuan snowball or a mostly frozen body with a substellar (region closest to its star) ocean that makes it look like a cosmic eyeball. It is now thought to be the exoplanet with the best chance for liquid water on its surface, and so might even be habitable.
Cadieux and his team say they have found “tantalizing evidence for a [nitrogen]-dominated atmosphere on a habitable zone super-Earth” in a study recently published in The Astrophysical Journal Letters.
Sorry, Neptune…
In December 2023, two transits of LHS 1140 b were observed with the NIRISS (Near-Infrared Imager and Slitless Spectrograph) instrument aboard Webb. NIRISS specializes in detecting exoplanets and revealing more about them through transit spectroscopy, which picks up the light of an orbiting planet’s host star as it passes through the atmosphere of that planet and travels toward Earth. Analysis of the different spectral bands in that light can then tell scientists about the specific atoms and molecules that exist in the planet’s atmosphere.
To test the previous hypothesis that LHS 1140 b is a mini-Neptune, the researchers created a 3D global climate model, or GCM. This used complex math to explore different combinations of factors that make up the climate system of a planet, such as land, oceans, ice, and atmosphere. Several different GCMs of a mini-Neptune were compared with the light spectrum observed via transit spectroscopy. The model for a mini-Neptune typically involves a gas giant with a thick, cloudless or nearly cloudless atmosphere dominated by hydrogen, but the spectral bands of this model did not match NIRISS observations.
With the possibility of a mini-Neptune being mostly ruled out (though further observations and analysis will be needed to confirm this), Cadieux’s team turned to another possibility: a super-Earth.
An Earth away from Earth?
The spectra observed with NIRISS were more in line with GCMs of a super-Earth. This type of planet would typically have a thick nitrogen or CO2-rich atmosphere enveloping a rocky surface on which there was some form of water, whether in frozen or liquid form.
The models also suggested a secondary atmosphere, which is an atmosphere formed after the original atmosphere of light elements, (hydrogen and helium) escaped during early phases of a planet’s formation. Secondary atmospheres are formed from heavier elements released from the crust, such as water vapor, carbon dioxide, and methane. They’re usually found on warm, terrestrial planets (Earth has a secondary atmosphere).
The most significant Webb/NIRISS data that did not match the GCMs was that the planet has a lower density (based on measurements of its size and mass) than expected for a rocky world. This is consistent with a water world with a mass that’s about 10 to 20 percent water. Based on this estimate, the researchers think that LHS 1140 b might even be a hycean planet—an ocean planet that has most of the attributes of a super-Earth, but an atmosphere dominated by hydrogen instead of nitrogen.
Since it orbits a dim star closely enough to be tidally locked, some models suggest a mostly icy planet with a substellar liquid ocean on its dayside.
While LHS 1140 b may be a super-Earth, the hycean planet hypothesis might end up being ruled out. Hycean planets are prone to the runaway greenhouse effect, which occurs when enough greenhouse gases accumulate in a planet’s atmosphere and prevent heat from escaping. Liquid water will eventually evaporate on a planet that cannot cool itself off.
Though we are getting closer to finding out what kind of planet LHS 1140 b is, and whether it could be habitable, further observations are needed. Cadieux wants to continue this research by comparing NIRISS data with data on other super-Earths that had previously been collected by Webb’s Near-Infrared Spectrograph, or NIRSpec, instrument. At least three transit observations of the planet with Webb’s MIRI, or Mid-Infrared instrument, are also needed to make sure stellar radiation is not interfering with observations of the planet itself.
“Given the limited visibility of LHS 1140b, several years’ worth of observations may be required to detect its potential secondary atmosphere,” the researchers said in the same study.
So could this planet really be a frozen exo-earth? The suspense is going to last a few years.
