It might not come as a surprise to learn that Lin is a badminton player. “The experience of playing badminton is really the thing that kick-started the idea and led me to ask the right questions,” he said.
Previous explanations attribute the dust alignment to the magnetic influence of the central star, the physics of which can be complicated and not always intuitive. The beauty of the proposed birdie mechanism is its simplicity. “It’s a very good first step,” said Bing Ren, an astronomer at France’s Côte d’Azur Observatory who wasn’t involved in the study.
Still, the birdie-alignment hypothesis is just that—a hypothesis. To confirm whether it holds water, scientists will need to throw their full observational arsenal at protoplanetary disks, such as viewing them at different wavelengths, to sniff out the finer details of particle-gas interactions.
Tracing invisible gas
Real-life protoplanetary disks are likely more complicated than a uniform squadron of space potatoes suspended in thin air. Ren suspects that the grains come in various shapes, sizes, and speeds. Nevertheless, he says Lin’s study is a good foundation for computer models of interstellar clouds, onto which scientists can tack layers of complexity.
The new research points a way forward for probing protoplanetary disks, particularly gas behavior. Given that the grains trace the gas direction, studying dust organization using existing tools like polarized light can allow scientists to map a disk’s aerodynamic flow. Essentially, these grains are tiny flags that signal where the wind blows.
As granular as the details are, the dust alignment is a small but key step in a grand journey of particle-to-planet progression. The nitty-gritty of a particle’s conduct will determine its fate for millions of years—perhaps the primordial seed will hoover up hydrogen and helium to become a gas giant or amass dust to transform into a terrestrial world like Earth. It all starts with it flailing or keeping steady amid a sea of other specks.
Shi En Kim is a DC-based freelance journalist who writes about health, the environment, technology, and the physical sciences. She and three other journalists founded Sequencer Magazine in early 2024. Occasionally, she creates art to accompany her writings or does it simply for fun. Follow her on Twitter at @goes_by_kim, or see more of her work on her personal website.
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/ One of the jets emitted by galaxy M87’s central black hole.
The intense electromagnetic environment near a black hole can accelerate particles to a large fraction of the speed of light and sends the speeding particles along jets that extend from each of the object’s poles. In the case of the supermassive black holes found in the center of galaxies, these jets are truly colossal, blasting material not just out of the galaxy, but possibly out of the galaxy’s entire neighborhood.
But this week, scientists have described how the jets may be doing some strange things inside of a galaxy, as well. A study of the galaxy M87 showed that nova explosions appear to be occurring at an unusual high frequency in the neighborhood of one of the jets from the galaxy’s central black hole. But there’s absolutely no mechanism to explain why this might happen, and there’s no sign that it’s happening at the jet that’s traveling in the opposite direction.
Whether this effect is real, and whether we can come up with an explanation for it, may take some further observations.
Novas and wedges
M87 is one of the larger galaxies in our local patch of the Universe, and its central black hole has active jets. During an earlier period of regular observations, the Hubble Space Telescope had found that stellar explosions called novas appeared to be clustered around the jet.
This makes very little sense. Novas occur in systems with a large, hydrogen-rich star, with a nearby white dwarf in orbit. Over time, the white dwarf draws hydrogen off the surface of its companion, until it reaches a critical mass on its surface. At that point, a thermonuclear explosion blasts the remaining material off the white dwarf, and the cycle resets. Since the rate of material transfer tends to be fairly stable, novas in a stellar system will often repeat at regular intervals. And it’s not at all clear why a black hole’s jet would alter that regularity.
So, some of the people involved in the first study got time on the Hubble to go back and have another look. And for a big chunk of a year, every five days, Hubble was pointed at M87, allowing it to capture novas before they faded back out. All told, this picked up 94 novas that occurred near the center of the galaxy. Combined with 41 that had been identified during earlier work, this left a collection of 135 novas in this galaxy. The researchers then plotted these relative to the black hole and its jets.
The area containing the jet (upper right) experiences significantly more novas than the rest of the galaxy’s core.
Lessing et. al.
Dividing the area around the center of the galaxy into 10 equal segments, the researchers counted the novas that occurred in each. In the nine segments that didn’t include the jet on the side of the galaxy facing Earth, the average number of novas was 12. In the segment that included the jet, the count was 25. Another way to look at this is that the highest count in a non-jet segment was only 16—and that was in a segment immediately next to the one with the jet in it. The researchers calculate the odds of this arrangement occurring at random as being about one in 1,310 (meaning less than 0.1 percent).
To get a separate measure of how unusual this is, the researchers placed 8 million novas around the center of the galaxy, with the distribution being random but biased to match the galaxy’s brightness under the assumption that novas will be more frequent in areas with more stars. This was then used to estimate how often novas should be expected in each of these segments. They then used a wide variety of wedges: “In order to reduce noise and avoid p-hacking when choosing the size of the wedge, we average the results for wedges between 30 and 45 degrees wide.”
Overall, the enhancement near the jet was low for either very narrow or very wide wedges, as you might expect—narrow wedges crop out too much of the area affected by the jet, while wide ones include a lot of space where you get the normal background rate. Things peak in the area of wedges that are 25 degrees wide, where the enrichment near the jet is about 2.6-fold. So, this appears to be real.
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/ 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/ The Wow! signal, represented as “6EQUJ5,” was discovered in 1977 by astronomer Jerry Ehman.
Public domain
An unusually bright burst of radio waves—dubbed the Wow! signal—discovered in the 1970s has baffled astronomers ever since, given the tantalizing possibility that it just might be from an alien civilization trying to communicate with us. A team of astronomers think they might have a better explanation, according to a preprint posted to the physics arXiv: clouds of atomic hydrogen that essentially act like a naturally occurring galactic maser, emitting a beam of intense microwave radiation when zapped by a flare from a passing magnetar.
As previously reported, the Wow! signal was detected on August 18, 1977, by The Ohio State University Radio Observatory, known as “Big Ear.” Astronomy professor Jerry Ehman was analyzing Big Ear data in the form of printouts that, to the untrained eye, looked like someone had simply smashed the number row of a typewriter with a preference for lower digits. Numbers and letters in the Big Ear data indicated, essentially, the intensity of the electromagnetic signal picked up by the telescope over time, starting at ones and moving up to letters in the double digits (A was 10, B was 11, and so on). Most of the page was covered in ones and twos, with a stray six or seven sprinkled in.
But that day, Ehman found an anomaly: 6EQUJ5 (sometimes misinterpreted as a message encoded in the radio signal). This signal had started out at an intensity of six—already an outlier on the page—climbed to E, then Q, peaked at U—the highest power signal Big Ear had ever seen—then decreased again. Ehman circled the sequence in red pen and wrote “Wow!” next to it. The signal appeared to be coming from the direction of the Sagittarius constellation, and the entire signal lasted for about 72 seconds. Alas, SETI researchers have never been able to detect the so-called “Wow! Signal” again, despite many tries with radio telescopes around the world.
One reason for the excited reaction is that such a signal had been proposed as a possible communication from extraterrestrial civilizations in a 1959 paper by Cornell University physicists Philip Morrison and Giuseppe Cocconi. Morrison and Cocconi thought that such a civilization might use the 1420 megahertz frequency naturally emitted by hydrogen, the universe’s most abundant element and, therefore, something an alien civilization would be familiar with. In fact, the Big Ear had been reassigned to the SETI project in 1973 specifically to hunt for possible signals. Ehman himself was quite skeptical of the “it could be aliens” hypothesis for several decades, although he admitted in a 2019 interview that “the Wow! signal certainly has the potential of being the first signal from extraterrestrial intelligence.”
Several other alternative hypotheses have been suggested. For instance, Antonio Paris suggested in 2016 that the signal may have come from the hydrogen cloud surrounding a pair of comets, 266P/Christensen and 335P/Gibbs. This was rejected by most astronomers, however, in part because comets don’t emit strongly at the relevant frequencies. Others have suggested the signal was the result of interference from satellites orbiting the Earth, or a signal from Earth reflected off a piece of space debris.
Space maser!
Astrobiologist Abel Mendez of the University of Puerto Rico at Arecibo and his co-authors think they have the strongest astrophysical explanation to date with their cosmic maser hypothesis. The team was actually hunting for habitable exoplanets using signals from red dwarf stars. In some of the last archival data collected at the Arecibo radio telescope (which collapsed in 2020), they noticed several signals that were remarkably similar to the Wow! signal in terms of frequency—just much less intense (bright).
Mendez admitted to Science News that he had always viewed the Wow! signal as just a fluke—he certainly didn’t think it was aliens. But he realized that if the signals they were identifying had blazed brighter, even momentarily, they would be very much like the Wow! signal. As for the mechanism that caused such a brightening, Mendez et al. propose that a magnetar (a highly magnetic neutron star) passing behind a cloud of atomic hydrogen could have flared up with sufficient energy to produce stimulated emission in the form of a tightly focused beam of microwave radiation—a cosmic maser. (Masers are akin to lasers, except they emit microwave radiation rather than visible radiation.)
Proving their working hypothesis will be much more challenging, although there have been rare sightings of such naturally occurring masers from hydrogen molecules in space. But nobody has ever spotted an atomic hydrogen cloud with an associated maser, and that’s what would be needed to explain the intensity of the Wow! signal. That’s why other astronomers are opting for cautious skepticism. “A magnetar is going to produce [short] radio emissions as well. Do you really need this complicated maser stuff happening as well to explain the Wow! signal?” Michael Garrett of the University of Manchester told New Scientist. “Personally, I don’t think so. It just makes a complicated story even more complicated.”
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/ A naked-eye sunspot group on May 11, 2024. There are typically 40,000 to 50,000 sunspots observed in ~11-year solar cycles.
E. T. H. Teague
A team of Japanese and Belgian astronomers has re-examined the sunspot drawings made by 17th century astronomer Johannes Kepler with modern analytical techniques. By doing so, they resolved a long-standing mystery about solar cycles during that period, according to a recent paper published in The Astrophysical Journal Letters.
Precisely who first observed sunspots was a matter of heated debate in the early 17th century. We now know that ancient Chinese astronomers between 364 and 28 BCE observed these features and included them in their official records. A Benedictine monk in 807 thought he’d observed Mercury passing in front of the Sun when, in reality, he had witnessed a sunspot; similar mistaken interpretations were also common in the 12th century. (An English monk made the first known drawings of sunspots in December 1128.)
English astronomer Thomas Harriot made the first telescope observations of sunspots in late 1610 and recorded them in his notebooks, as did Galileo around the same time, although the latter did not publish a scientific paper on sunspots (accompanied by sketches) until 1613. Galileo also argued that the spots were not, as some believed, solar satellites but more like clouds in the atmosphere or the surface of the Sun. But he was not the first to suggest this; that credit belongs to Dutch astronomer Johannes Fabricus, who published his scientific treatise on sunspots in 1611.
Kepler read that particular treatise and admired it, having made his sunspot observations using a camera obscura in 1607 (published in a 1609 treatise), which he initially thought was a transit of Mercury. He retracted that report in 1618, concluding that he had actually seen a group of sunspots. Kepler made his solar drawings based on observations conducted both in his own house and in the workshop of court mechanic Justus Burgi in Prague. In the first case, he reported “a small spot in the size of a small fly”; in the second, “a small spot of deep darkness toward the center… in size and appearance like a thin flea.”
Enlarge/ The earliest datable sunspot drawings based on Kepler’s solar observations with camera obscura in May 1607.
Public domain
The long-standing debate that is the subject of this latest paper concerns the period from around 1645 to 1715, during which there were very few recorded observations of sunspots despite the best efforts of astronomers. This was a unique event in astronomical history. Despite only observing some 59 sunspots during this time—compared to between 40,000 to 50,000 sunspots over a similar time span in our current age—astronomers were nonetheless able to determine that sunspots seemed to occur in 11-year cycles.
German astronomer Gustav Spörer noted the steep decline in 1887 and 1889 papers, and his British colleagues, Edward and Annie Maunder, expanded on that work to study how the latitudes of sunspots changed over time. That period became known as the “Maunder Minimum.” Spörer also came up with “Spörer’s law,” which holds that spots at the start of a cycle appear at higher latitudes in the Sun’s northern hemisphere, moving to successively lower latitudes in the southern hemisphere as the cycle runs its course until a new cycle of sunspots begins in the higher latitudes.
But precisely how the solar cycle transitioned to the Maunder Minimum has been far from clear. Reconstructions based on tree rings have produced conflicting data. For instance, one such reconstruction concluded that the gradual transition was preceded either by an extremely short solar cycle of about five years or an extremely long solar cycle of about 16 years. Another tree ring reconstruction concluded the solar cycle would have been of normal 11-year duration.
Independent observational records can help resolve the discrepancy. That’s why Hisashi Hayakawa of Nagoya University in Japan and co-authors turned to Kepler’s drawings of sunspots for additional insight, which predate existing telescopic observations by several years.
Enlarge/ Some of the galaxies in the JADES images.
One of the things that the James Webb Space Telescope was designed to do was look at some of the earliest objects in the Universe. And it has already succeeded spectacularly, imaging galaxies as they existed just 250 million years after the Big Bang. But these galaxies were small, compact, and similar in scope to what we’d consider a dwarf galaxy today, which made it difficult to determine what was producing their light: stars or an actively feeding supermassive black hole at their core.
This week, Nature is publishing confirmation that some additional galaxies we’ve imaged also date back to just 300 million years after the Big Bang. Critically, one of them is bright and relatively large, allowing us to infer that most of its light was coming from a halo of stars surrounding its core, rather than originating in the same area as the central black hole. The finding implies that it formed through a continuing burst of star formation that started just 200 million years after the Big Bang.
Age checks
The galaxies at issue here were first imaged during the JADES (JWST Advanced Deep Extragalactic Survey) imaging program, which includes part of the area imaged for the Hubble Ultra Deep Field. Initially, old galaxies were identified by using a combination of filters on one of Webb’s infrared imaging cameras.
Most of the Universe is made of hydrogen, and figuring out the age of early galaxies involves looking for the most energetic transitions of hydrogen’s electron, called the Lyman series. These transitions produce photons that are in the UV area of the spectrum. But the redshift of light that’s traveled for billions of years will shift these photons into the infrared area of the spectrum, which is what Webb was designed to detect.
What this looks like in practice is that hydrogen-dominated material will emit a broad range of light right up to the highest energy Lyman transition. Above that energy, photons will be sparse (they may still be produced by things like processes that accelerate particles). This point in the energy spectrum is called the “Lyman break,” and its location on the spectrum will change based on how distant the source is—the greater the distance to the source, the deeper into the infrared the break will appear.
Initial surveys checked for the Lyman break using filters on Webb’s cameras that cut off different areas of the IR spectrum. Researchers looked for objects that showed up at low energies but disappeared when a filter that selected for higher-energy infrared photons was swapped in. The difference in energies between the photons allowed through by the two filters can provide a rough estimate of where the Lyman break must be.
Locating the Lyman break requires imaging with a spectrograph, which can sample the full spectrum of near-infrared light. Fortunately, Webb has one of those, too. The newly published study involved turning the NIRSpec onto three early galaxies found in the JADES images.
Too many, too soon
The researchers involved in the analysis only ended up with data from two of these galaxies. NIRSpec doesn’t gather as much light as one of Webb’s cameras can, and so the faintest of the three just didn’t produce enough data to enable analysis. The other two, however, produced very clear data that placed the galaxies at a redshift measure roughly z = 14, which means we’re seeing them as they looked 300 million years after the Big Bang. Both show sharp Lyman breaks, with the amount of light dropping gradually as you move further into the lower-energy part of the spectrum.
There’s a slight hint of emissions from heavily ionized carbon atoms in one of the galaxies, but no sign of any other specific elements beyond hydrogen.
One of the two galaxies was quite compact, so similar to the other galaxies of this age that we’d confirmed previously. But the other, JADES-GS-ZZ14-0, was quite distinct. For starters, it’s extremely bright, being the third most luminous distant galaxy out of hundreds we’ve imaged so far. And it’s big enough that it’s not possible for all its light to be originating from the core. That rules out the possibility that what we’re looking at is a blurred view of an active galactic nucleus powered by a supermassive black hole feeding on material.
Instead, much of the light we’re looking at seems to have originated in the stars of JADES-GS-ZZ14-0. Most of those stars are young, and there seems to be very little of the dust that characterizes modern galaxies. The researchers estimate that star formation started at least 100 million years earlier (meaning just 200 million years after the Big Bang) and continued at a rapid pace in the intervening time.
Combined with earlier data, the researchers write that this confirms that “bright and massive galaxies existed already only 300 [million years] after the Big Bang, and their number density is more than ten times higher than extrapolations based on pre-JWST observations.” In other words, there were a lot more galaxies around in the early Universe than we thought, which could pose some problems for our understanding of the Universe’s contents and their evolution.
Meanwhile, the early discovery of the extremely bright galaxy implies that there are a number of similar ones out there awaiting our discovery. This means there’s going to be a lot of demand for time on NIRSpec in the coming years.
Enlarge/ A jet of particles moving at nearly light-speed emerges from a massive star in this artist’s concept of the BOAT.
NASA’s Goddard Space Flight Center Conceptual Image Lab
Scientists have been all aflutter since several space-based detectors picked up a powerful gamma-ray burst (GRB) in October 2022—a burst so energetic that astronomers nicknamed it the BOAT (Brightest Of All Time). Now an international team of astronomers has analyzed an unusual energy peak detected by NASA’s Fermi Gamma-ray Space Telescope and concluded that it was an emission spectra, according to a new paper published in the journal Science. Per the authors, it’s the first high-confidence emission line ever seen in 50 years of studying GRBs.
As reported previously, gamma-ray bursts are extremely high-energy explosions in distant galaxies lasting between mere milliseconds to several hours. There are two classes of gamma-ray bursts. Most (70 percent) are long bursts lasting more than two seconds, often with a bright afterglow. These are usually linked to galaxies with rapid star formation. Astronomers think that long bursts are tied to the deaths of massive stars collapsing to form a neutron star or black hole (or, alternatively, a newly formed magnetar). The baby black hole would produce jets of highly energetic particles moving near the speed of light, powerful enough to pierce through the remains of the progenitor star, emitting X-rays and gamma rays.
Those gamma-ray bursts lasting less than two seconds (about 30 percent) are deemed short bursts, usually emitting from regions with very little star formation. Astronomers think these gamma-ray bursts are the result of mergers between two neutron stars, or a neutron star merging with a black hole, comprising a “kilonova.” That hypothesis was confirmed in 2017 when the LIGO collaboration picked up the gravitational wave signal of two neutron stars merging, accompanied by the powerful gamma-ray bursts associated with a kilonova.
Several papers were published last year reporting on the analytical results of all the observational data. Those findings confirmed that GRB 221009A was indeed the BOAT, appearing especially bright because its narrow jet was pointing directly at Earth. But the various analyses also yielded several surprising results that puzzled astronomers. Most notably, a supernova should have occurred a few weeks after the initial burst, but astronomers didn’t detect one, perhaps because it was very faint, and thick dust clouds in that part of the sky were dimming any incoming light.
Earlier this year, astronomers confirmed that the BOAT came from a supernova, thanks to the telltale signatures of key elements like calcium and oxygen that one would expect to find with a supernova. However, they did not find evidence of the expected heavy elements like platinum and gold, which bears on the longstanding question of the origin of such elements in the universe. The BOAT might just be special in that regard; further data will tell us more.
“It gave me goosebumps”
A few minutes after the BOAT erupted, Fermi’s Gamma-ray Burst Monitor recorded an unusual energy peak. Scientists now say this feature is the first high-confidence emission line ever seen in 50 years of studying GRBs.
The newly detected spectral emission line was likely caused by the collision of matter and anti-matter, according to the authors, producing a pair of gamma rays that are blue-shifted toward higher energies because we are looking into the jet. Having a spectral emission associated with a GRB is important because it can shed light on the specific chemicals involved in the interactions. There have been prior studies reporting possible evidence for absorption or emission lines in other GRBs, but they have usually turned out likely to be statistical noise.
That’s not the case with this latest detection, according to co-author Om Sharan Salafia at INAF-Brera Observatory in Milan, Italy, who added that the odds of this turning out to be a statistical fluctuation “are less than one chance in half a billion.” His INAF colleague and co-author, Maria Edvige Ravasio, said that when she first saw the signal, “it gave me goosebumps.”
Why did astronomers take so long to detect it? When the BOAT first erupted in 2022, it saturated most of the space-based gamma-ray detectors, including the Fermi Space Telescope, making them unable to measure the most intense part of that blast. The emission line didn’t appear until a good five minutes after the burst when it had sufficiently dimmed for Fermi to make a measurement. The spectral emission lasted for about 40 seconds and reached a peak energy of about 12 MeV, compared to 2 or 3 MeB for visible light, per the authors.
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.
