In a solar system about 1,800 light-years from Earth, two planets smacked into one another in an impact that vaporized them both. And astronomers caught them in the act.

An incandescent blob of leftover planet, lingering after an impact, could explain a surge of infrared light from a remote star, researchers report October 11 in Nature. And the ensuing debris field could also explain a subsequent dimming of the star, the team says. While scientists have glimpsed planetary debris in other solar systems before, no one has seen the smoldering remains of a collision between exoplanets until now (SN: 5/8/23).

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“The possible detection of a post-impact body is really exciting,” says astrophysicist Philip Carter of the University of Bristol in England, who was not involved in the new study. “As far as I’m aware, no one’s claimed this before.”

As is often the case for exciting astronomical discoveries, detecting the aftermath of this cosmic smackdown involved more than a little luck.

Astronomer Matthew Kenworthy wasn’t hunting for giant impacts. “I was looking for rings” around exoplanets, he says (SN: 2/1/15). So he was scouring telescope survey data for stars that flicker or dim in unusual ways. And when the ASAS-SN survey — an ongoing project to monitor the entire sky for exploding stars — captured the sunlike star ASASSN-21qj repeatedly dimming in visible light, “I immediately jumped on it,” says Kenworthy, of Leiden Observatory in the Netherlands.

As he was analyzing the fading star, Kenworthy stumbled upon another clue — on social media. One of his posts on Twitter (now called X) about ASASSN-21qj’s unusual behavior caught the eye of citizen scientist Arttu Sainio. “I tweeted out saying: ‘Oh, this is amazing, this star is fading!’” Kenworthy says. “Then he said: ‘Oh, by the way, did you realize the star had brightened up [in infrared]?’”

Sainio pointed out that infrared data from NASA’s orbiting WISE telescope showed a strong uptick in infrared radiation from the star about 900 days before the dimming started. Kenworthy’s hopes for rings were dashed. But maybe he and his colleagues had found something else just as fascinating.

“It just totally changed the story,” Kenworthy says.

The researchers realized that a giant impact could neatly tie together the spontaneous infrared glow and the visible light dimming that followed more than two years later. Their calculations suggest that two Neptune-sized planets collided, vaporizing each other and forming a hot, donut-shaped body of vaporized rock — the source of the infrared glow. ASASSN-21qj later dimmed when impact debris smeared out around the star and blocked some of its light.

[embedded content]
Two exoplanets collided in a smashup that left behind a glob of hot, vaporized rock and a debris cloud. Astronomers first observed the afterglow of the collision in infrared light. Then, 900 days later, they saw the pulverized planets’ star dim as impact debris drifted in front of it, between the star and Earth.

Alternatively, it’s possible that astronomers observed two separate events: an infrared glow from dust warmed by starlight, perhaps left behind by a collision between close-orbiting protoplanets, followed by dimming as a big disk of unrelated material passed in front of the star. But two rare events happening in close succession is “really, really, really unlikely,” Kenworthy says.

The putative post-impact blob could one day coalesce into a planet. And as the remaining debris shears out into a disk orbiting the star, it too might eventually collect onto the new planet or form moons around it.

How long all that might take isn’t clear, Carter says. It could happen within a few years or perhaps several thousand. “The models of these impact remnants are still in the very early stages,” he says. Either way, continuing to observe the post-impact material over the coming years will give scientists a rare chance to witness, not just simulate, what happens after a planetary collision.

“You expect astronomical processes to take astronomical amounts of time. And it’s like: Nope! This was very fast. This happened over just a few years,” Kenworthy says. “It’ll just be fascinating to see how it evolves over time, in the next 10 or 20 years.” More

Meteorites offer tantalizing clues about what the early solar system was like. But finding them is far from rocket science. Often, researchers simply fan out across a landscape and walk for hours while staring at the ground. Now, some scientists are turning to drones and machine learning to help spot freshly fallen meteorites much more efficiently.

A team of six people on a meteorite-hunting expedition can search about 200,000 square meters per day, says Seamus Anderson, a planetary scientist at Curtin University in Perth, Australia. But since the area over which a cluster of meteorites falls typically can’t be pinpointed to better than a few million square meters, searching can take a while, he says. “It’s quite slow.”

Seamus Anderson (pictured) and his colleagues used a drone to find a meteorite in Western Australia in 2021.The Desert Fireball Network

Around 2016, Anderson began toying with the concept of using drones to take pictures of the ground to look for meteorites. That idea blossomed into a Ph.D. project. In 2022, he and his colleagues reported their first successful recovery of a meteorite spotted with a drone. They’ve since found four more meteorites at a different site, the team reported August 17 in Los Angeles at a meeting of the Meteoritical Society.

Drone-based searches are much faster than the standard way of doing things, Anderson says. “You’re going from about 300 days of human effort down to about a dozen or so.” It’s also fun and exciting work, he says, but there are challenges too.

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Anderson and his collaborators have used drones to search for meteorites in remote parts of Western Australia and South Australia. The team is tipped off about a fall site by networks of ground-based cameras that track meteoroids flashing through Earth’s atmosphere. Then, the hunt is on.

The researchers pack a four-wheel drive vehicle with drone and computer equipment, battery charging stations, generators, fuel, food, camping equipment, tables, chairs and more. The drive to the fall site can take more than a day, often on rough or nonexistent roads, Anderson says. “You hope you don’t pop a tire.”

After arriving, the team flies its primary drone at an altitude of about 20 meters. Its camera takes an image of the ground once every second, and the researchers download the data every 40 minutes or so when the drone lands to receive fresh batteries.

A typical day of flying can net over 10,000 images, which are then divided digitally into 100 million or so smaller sections. Those “tiles,” each 2 meters on a side, are fed into a machine learning algorithm that has been trained to recognize meteorites based on images of the real thing or terrestrial rocks spray-painted black. The latter are convincing stand-ins for real meteorites, Anderson says.

The algorithm is good but not perfect. It automatically discards most tiles — typically upwards of 99 percent — that don’t contain any meteorite-looking objects. But that still leaves roughly 50,000 or so tiles after a day’s worth of flights that must be manually checked by a human, Anderson says.

A machine learning algorithm, trained to identify potential meteorites in drone images, can mistake sleeping kangaroos (indicated with yellow squares) for space rocks. Researchers are working on improving the algorithm further.The Desert Fireball Network

Most of the time, those tiles contain things that decidedly aren’t meteorites: animal poop, tin cans, snakes or sleeping kangaroos, for instance. Those objects get flagged as potential meteorites simply because the algorithm isn’t familiar with them, Anderson says, and it’s up to the team to winnow out those false positives.

For objects that still look convincing to the human eye, the researchers send out a smaller drone that flies much lower — about a meter off the ground — to investigate. Finally, the team goes out in person to examine promising candidates.

The researchers plan to train their algorithm to better avoid flagging things like poop and kangaroos as meteorites. And the team is working on making its computer code open-source so that other researchers can freely use it.

Anderson also hopes to see drones make an appearance in Antarctica, a hotbed of meteorite sleuthing (SN: 1/26/22). But the icy environment will present a whole new slew of challenges, Anderson says, such as making sure sensitive electronic equipment fares well in the frigid conditions and overcoming the logistics of working in such a remote place. “Antarctica is a whole different beast.” More

For the first time, astronomers have observed how certain supermassive black holes launch jets of high-energy particles into space — and the process is shocking.

Shock waves propagating along the jet of one such blazar contort magnetic fields that accelerate escaping particles to nearly the speed of light, astronomers report November 23 in Nature. Studying such extreme acceleration can help probe fundamental physics questions that can’t be studied any other way.

Blazars are active black holes that shoot jets of high-energy particles toward Earth, making them appear as bright spots from millions or even billions of light-years away (SN: 7/14/15). Astronomers knew that the jets’ extreme speeds and tight columnated beams had something to do with the shape of magnetic fields around black holes, but the details were fuzzy.

Enter the Imaging X-Ray Polarimetry Explorer, or IXPE, an orbiting telescope launched in December 2021. Its mission is to measure X-ray polarization, or how X-ray light is oriented as it travels through space. While previous blazar observations of polarized radio waves and optical light probed parts of jets days to years after they’d been accelerated, polarized X-rays can see into a blazar’s active core (SN: 3/24/21).

“In X-rays, you’re really looking at the heart of the particle acceleration,” says astrophysicist Yannis Liodakis of the University of Turku in Finland. “You’re really looking at the region where everything happens.”

In March 2022, IPXE looked at an especially bright blazar called Markarian 501, located about 450 million light-years from Earth.

Liodakis and colleagues had two main ideas for how magnetic fields might accelerate Markarian 501’s jet. Particles could be boosted by magnetic reconnection, where magnetic field lines break, reform and connect with other nearby lines. The same process accelerates plasma on the sun (SN: 11/14/19). If that was the particle acceleration engine, the polarization of light should be the same along the jet in all wavelengths, from radio waves to X-rays.

Another option is a shock wave shooting particles down the jet. At the site of the shock, the magnetic fields suddenly switch from turbulent to ordered. That switch could send particles zooming away, like water through the nozzle of a hose. As the particles leave the shock site, turbulence should take over again. If a shock was responsible for the acceleration, short wavelength X-rays should be more polarized than longer wavelength optical and radio light, as measured by other telescopes.

The IXPE spacecraft (illustrated) observed polarized X-rays come from a blazar and its jet. The inset illustrates how particles in the jet hit a shock wave (white) and get boosted to extreme speeds, emitting high-energy X-ray light. As they lose energy, the particles emit lower energy light in visible, infrared and radio wavelengths (purple and blue), and the jet becomes more turbulent.Pablo Garcia/MSFC/NASA

That’s exactly what the researchers saw, Liodakis says. “We got a clear result,” he says, that favors the shock wave explanation.

There is still work to do to figure out the details of how the particles flow, says astrophysicist James Webb of Florida International University in Miami. For one, it’s not clear what would produce the shock. But “this is a step in the right direction,” he says. “It’s like opening a new window and looking at the object freshly, and we now see things we hadn’t seen before. It’s very exciting.” More

Clouds of sand can condense, grow and disappear in some extraterrestrial atmospheres. A new look at old data shows that clouds made of hot silicate minerals are common in celestial objects known as brown dwarfs.

“This is the first full contextual understanding of any cloud outside the solar system,” says astronomer Stanimir Metchev of the University of Western Ontario in London, Canada. Metchev’s colleague Genaro Suárez presented the new work July 4 at the Cool Stars meeting in Toulouse, France.

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Clouds come in many flavors in our solar system, from Earth’s puffs of water vapor to Jupiter’s bands of ammonia. Astronomers have also inferred the presence of “extrasolar clouds” on planets outside the solar system (SN: 9/11/19).

But the only extrasolar clouds that have been directly detected were in the skies of brown dwarfs — dim, ruddy orbs that are too large to be planets but too small and cool to be stars. In 2004, astronomers used NASA’s Spitzer Space Telescope to observe brown dwarfs and spotted spectral signatures of sand — more specifically, grains of silicate minerals such as quartz and olivine. A few more tentative examples of sand clouds were spotted in 2006 and 2008.

Floating in one of these clouds would feel like being in a sandstorm, says planetary scientist Mark Marley of the University of Arizona in Tucson, who was involved in one of those early discoveries. “If you could take a scoop out of it and bring it home, you would have hot sand.”

Astronomers at the time found six examples of these silicate clouds. “I kind of thought that was it,” Marley says. Theoretically, there should be a lot more than six brown dwarfs with sandy skies. But part of the Spitzer telescope ran out of coolant in 2009 and was no longer able to measure similar clouds’ chemistry.

While Suárez was looking into archived Spitzer data for a different project, he realized there were unpublished or unanalyzed data on dozens of brown dwarfs. So he analyzed all of the low-mass stars and brown dwarfs that Spitzer had ever observed, 113 objects in total, 68 of which had never been published before, the team reports in the July Monthly Notices of the Royal Astronomical Society.

“It’s very impressive to me that this was hiding in plain sight,” Marley says.

Not every brown dwarf in the sample showed strong signs of silicate clouds. But together, the brown dwarfs followed a clear trend. For dwarfs and low-mass stars hotter than about 1700˚ Celsius, silicates exist as a vapor, and the objects show no signs of clouds. But below that temperature, signs of clouds start to appear, becoming thickest around 1300˚ C. Then the signal disappears for brown dwarfs that are cooler than about 1000˚ C, as the clouds sink deep into the atmospheres.

The finding confirms previous suspicions that silicate clouds are widespread and reveals the conditions under which they form. Because brown dwarfs are born hot and cool down over time, most of them should see each phase of sand cloud evolution as they age. “We are learning how these brown dwarfs live,” Suárez says. Future research can extrapolate the results to better understand atmospheres in planets like Jupiter, he notes.

The recently launched James Webb Space Telescope will also study atmospheric chemistry in exoplanets and brown dwarfs and will specifically look for clouds (SN: 10/6/21). Marley looks forward to combining the trends from this study with future results from JWST. “It’s really going to be a renaissance in brown dwarf science,” he says. More

An uncanny resemblance to the Death Star might not be the only intriguing thing about Saturn’s moon Mimas. It could also harbor a vast ocean of liquid water beneath its pockmarked exterior.

A new look at data from NASA’s Cassini probe reveals that the point in Mimas’ orbit where it comes closest to Saturn changed slightly over 13 years, researchers report February 7 in Nature. Because Mimas’ internal composition affects the gravitational dance between the moon and its planet, these orbital dynamics, along with some previously seen moon wobbles, point to a liquid interior, astronomer Valéry Lainey of the Paris Observatory and colleagues say. More