Eliana Willis

It worked! Humanity has, for the first time, purposely moved a celestial object.

As a test of a potential asteroid-deflection scheme, NASA’s DART spacecraft shortened the orbit of asteroid Dimorphos by 32 minutes — a far greater change than astronomers expected.

The Double Asteroid Redirection Test, or DART, rammed into the tiny asteroid at about 22,500 kilometers per hour on September 26 (SN: 9/26/22). The goal was to move Dimorphos slightly closer to the larger asteroid it orbits, Didymos.

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Neither Dimorphos nor Didymos pose any threat to Earth. DART’s mission was to help scientists figure out if a similar impact could nudge a potentially hazardous asteroid out of harm’s way before it hits our planet.

The experiment was a smashing success. Before the impact, Dimorphos orbited Didymos every 11 hours and 55 minutes. After, the orbit was 11 hours and 23 minutes, NASA announced October 11 in a news briefing.

A small spacecraft called LICIACube, short for Light Italian CubeSat for Imaging of Asteroids, detached from DART just before impact, then buzzed the two asteroids to get a closeup view of the cosmic smashup. Starting from about 700 kilometers away, this series of images captures a bright plume of debris erupting from Dimorphos (right in the first half of this gif), evidence of the impact that shortened its orbit around Didymos (left). At closest approach, LICIACube was about 59 kilometers from the asteroids.ASI, NASA

“For the first time ever, humanity has changed the orbit of a planetary body,” said NASA planetary science division director Lori Glaze.

Four telescopes in Chile and South Africa observed the asteroids every night after the impact. The telescopes can’t see the asteroids separately, but they can detect periodic changes in brightness as the asteroids eclipse each other. All four telescopes saw eclipses consistent with an 11-hour, 23-minute orbit. The result was confirmed by two planetary radar facilities, which bounced radio waves off the asteroids to measure their orbits directly, said Nancy Chabot, a planetary scientist at Johns Hopkins Applied Physics Laboratory in Laurel, Md.

The minimum change for the DART team to declare success was 73 seconds — a hurdle the mission overshot by more than 30 minutes. The team thinks the spectacular plume of debris that the impactor kicked up gave the mission extra oomph. The impact itself gave some momentum to the asteroid, but the debris flying off in the other direction pushed it even more — like a temporary rocket engine.

“This is a very exciting and promising result for planetary defense,” Chabot said. But the change in orbital period was just 4 percent. “It just gave it a small nudge,” she said. So knowing an asteroid is coming is crucial to future success. For something similar to work on an asteroid headed for Earth, “you’d want to do it years in advance,” Chabot said. An upcoming space telescope called Near Earth Asteroid Surveyor is one of many projects intended to give that early warning. More

“Follow the water” has long been the mantra of scientists searching for life beyond Earth. After all, the only known cradle of life in the cosmos is the watery planet we call home. But now there’s more evidence suggesting that a potential discovery of liquid water on Mars might not be so watertight, researchers report September 26 in Nature Astronomy.

In 2018, scientists announced the discovery of a large subsurface lake near Mars’ south pole (SN: 7/25/18). That claim — and follow-up observations suggesting additional buried pools of liquid water on the Red Planet (SN: 9/28/20) — fueled excitement about finally finding an extraterrestrial world possibly conducive to life.

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But researchers have since proposed that those discoveries might not hold up to scrutiny. In 2021, one group suggested that clay minerals and frozen brines, rather than liquid water, might be responsible for the strong radar signals that researchers observed (SN: 7/16/21). Spacecraft orbiting Mars beam radio waves toward the Red Planet and measure the timing and intensity of the reflected waves to infer what’s beneath the Martian surface.   

And now another team has shown that ordinary layers of rock and ice can produce many of the same radar signals previously attributed to water. Planetary scientist Dan Lalich of Cornell University and his colleagues calculated how flat layers of bedrock, water ice and carbon dioxide ice — all known to be plentiful on Mars — reflect radio waves. “It was a pretty simple analysis,” Lalich says.

The researchers found that they could reproduce some of the anomalously strong radar signals thought to be due to liquid water. Individual radar signals from different layers of rock and ice add together when the layers are a certain thickness, Lalich says. That produces a stronger signal, which is then picked up by a spacecraft’s instruments. But those instruments can’t always tell the difference between a radio wave coming from one layer and one that’s the result of multiple layers, he says. “They look like one reflection to the radar.”

These results don’t rule out liquid water on Mars, Lalich and his colleagues acknowledge. “This is just saying that there are other options,” he says.

The new finding is “a plausible scenario,” says Aditya Khuller, a planetary scientist at Arizona State University in Tempe who was not involved in the research. But until scientists get a lot more data from the Red Planet, it’ll be difficult to know whether liquid water truly exists on Mars, Khuller says. “It’s important to be open-minded at this point.” More

Visitors to the village of Drumnadrochit, on the western shore of Scotland’s murky Loch Ness, come to see the nearby ruins of Urquhart Castle or to chance a glimpse of the elusive Loch Ness Monster. But growing up in Drumnadrochit, planetary scientist Robin Wordsworth says it was the unobscured view of the cosmos that seized his attention. “There are incredibly clear skies up there,” he says.

Today, Wordsworth lives on the other side of the Atlantic. He’s a researcher and professor at Harvard University. But his gaze is still set on the solar system and beyond. From studying how rocky planets may occasionally become encased in glaciers to exploring the sizes of alien raindrops or the details of how humans might one day settle Mars, Wordsworth’s scientific explorations vary widely. His research group tends to “do a lot of different things at once,” he says. “If I was to summarize it in a sentence, it would be to understand what drives habitability on planets through time.”

Standout research

Wordsworth defines a planet’s habitability as its ability to support life. The idea that life could survive elsewhere in the cosmos has always fascinated Wordsworth, a science fiction fan. Apart from Earth, astronomers have discovered roughly 20 potentially habitable worlds in the universe. With data collected by ground-based observatories, satellites and rovers, he uses supercomputers to construct simulations of planets and the evolution of their climates. Climate is a big focus because it determines whether a planet’s surface can harbor liquid water — a necessity for all known forms of life. 

The swirling clouds of Jupiter, captured by NASA’s Juno spacecraft, could release semisolid ammonia slushballs of precipitation. Work by Robin Wordsworth and a colleague suggests that the size of such alien raindrops is similar no matter what they’re made of or what planet they fall on.GERALD EICHSTADT/MSSS/SWRI, JPL-CALTECH/NASA

Wordsworth’s most notable research reconstructs the climate of early Mars. Martian river valleys and other geologic clues suggest that abundant liquid water once flowed across the Red Planet, and the early Martian climate has thus become a hot topic for scientists seeking signs of alien life. But for decades, the best researchers could do was build one-dimensional models that struggled to replicate key atmospheric components, such as clouds.

In 2013 while at the Laboratory of Dynamic Meteorology in Paris, Wordsworth and colleagues presented a 3-D model of the early Martian climate, with clouds and an atmosphere containing large amounts of carbon dioxide. Those are key components for studying how the early Martian atmosphere may have reflected and trapped heat, says astrobiologist James Kasting of Penn State.

Wordsworth was the one who figured out how to incorporate clouds into the model, thanks to his strong programming skills, handle over mathematics and determination, Kasting says. “He’s been publishing the best climate calculations for early Mars. There’s really nobody else who is in his lane.”

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What’s next

Wordsworth’s otherworldly reconstructions may help us better understand whether life might have emerged on Mars or elsewhere. Another strand of his research could help humans one day settle the Red Planet.

Today, most of Mars’ surface is too cold to sustain liquid water, and the planet’s thin atmosphere offers little protection from the sun’s intense ultraviolet radiation. These conditions make it inhospitable to would-be Martian settlers. But in a 2019 study, Wordsworth and colleagues proposed that sheets of insulating silica aerogel deployed over ice-covered areas might make survival possible.

In lab tests, layers of aerogel just centimeters thick filtered out 60 percent of UVA and UVB radiation and almost all of the more dangerous UVC rays, while permitting enough light through for photosynthesis. What’s more, the shields warmed the air underneath by more than 50 degrees Celsius, which could make liquid water and growing crops possible. Looking ahead, Wordsworth plans to investigate how settlers on Mars might use bioplastics or other renewable materials to become self-sustaining.

And far beyond the Red Planet, the exoplanets await. “The James Webb Space Telescope has just begun to collect new exoplanet data,” Wordsworth says. Observations of their atmospheres will help researchers test ideas about how these distant planets and their climates evolve, he says. “It’s just an incredibly exciting time.”

Want to nominate someone for the next SN 10 list? Send their name, affiliation and a few sentences about them and their work to sn10@sciencenews.org. More

Mission control rooms rarely celebrate crash landings. But the collision of NASA’s DART spacecraft with an asteroid was a smashing success.

At about 7:15 p.m. EDT on September 26, the spacecraft hurtled into Dimorphos, an asteroid moonlet orbiting a larger space rock named Didymos. The mission’s goal was to bump Dimorphos slightly closer to its parent asteroid, shortening its 12-hour orbit around Didymos by several minutes.

The Double Asteroid Redirection Test, or DART, is the world’s first attempt to change an asteroid’s motion by ramming a space probe into it (SN: 6/30/20). Neither Dimorphos nor Didymos poses a threat to Earth. But seeing how well DART’s maneuver worked will reveal how easy it is to tamper with an asteroid’s trajectory — a strategy that could protect the planet if a large asteroid is ever discovered on a collision course with Earth.

“We don’t know of any large asteroids that would be considered a threat to Earth that are coming any time in the next century,” says DART team member Angela Stickle, a planetary scientist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md. “The reason that we are doing something like DART is because there are asteroids that we haven’t discovered yet.”

NASA’s DART spacecraft (illustrated) just crashed into the asteroid moonlet Dimorphos on purpose in the world’s first test of a strategy for planetary defense.Johns Hopkins APL/NASA

Astronomers have spotted almost all the kilometer-size asteroids in the solar system that could end civilization if they hit Earth, says Jessica Sunshine, a planetary scientist at the University of Maryland in College Park who’s also on the DART team. But when it comes to space rocks around 150 meters wide, like Dimorphos, “we only know where about 40 percent of those are,” Sunshine says. “And that is something that, if it did hit, would certainly take out a city.”

Dimorphos is a safe asteroid to give an experimental nudge, says Mark Boslough, a physicist at Los Alamos National Laboratory in New Mexico who has studied planetary protection but is not involved in DART. “It’s not on a collision course” with Earth, he says, and DART “can’t hit it hard enough to put it on a collision course.” The DART spacecraft weighs only as much as a couple of vending machines, whereas Dimorphos is thought to be nearly as hefty as Egypt’s Great Pyramid of Giza.

After a 10-month voyage, DART met up with Didymos and Dimorphos near their closest approach to Earth, about 11 million kilometers away. Up until the very end of its journey, DART could see only the larger asteroid, Didymos. But about an hour before impact, DART spotted Dimorphos in its field of view. Using its onboard camera, the spacecraft steered itself toward the asteroid moonlet and slammed into it at some 6.1 kilometers per second, or nearly 14,000 miles per hour.

After traveling about 11 million kilometers, NASA’s DART spacecraft closed in on its target: the asteroid moonlet Dimorphos. This image of the space rock was taken by DART just seconds  before the spacecraft smashed into it. NASA

DART’s camera feed went dark after impact. But another probe nearby is expected to have caught the collision on camera. The Light Italian CubeSat for Imaging of Asteroids rode to Dimorphos aboard DART but detached a couple of weeks before impact to watch the event from a safe distance. Its mission was to whiz past Dimorphos about three minutes after DART’s impact to snap pictures of the crash site and the resulting plume of asteroid debris launched into space. The probe is expected to beam images of DART’s demise back to Earth within a couple of days.

“I was absolutely elated, especially as we saw the camera getting closer and just realizing all the science that we’re going to learn,” said Pam Melroy, NASA Deputy Administrator, after the impact. “But the best part was seeing, at the end, that there was no question there was going to be an impact, and to see the team overjoyed with their success.”

[embedded content]
This animation shows how DART’s impact on Dimorphos will affect the space rock’s orbit around its larger parent asteroid, Didymos. DART should shove Dimorphos into a slightly tighter, shorter orbit.

DART’s impact is expected to shove Dimorphos into a closer, shorter orbit around Didymos. Telescopes on Earth can clock the timing of that orbit by watching how the amount of light from the double asteroid system changes as Dimorphos passes in front of and behind Didymos.

“It’s really a beautifully conceived experiment,” Boslough says. In the coming weeks, dozens of telescopes across every continent will watch Dimorphos to see how much DART changed its orbit. The Hubble and James Webb space telescopes may also get images.

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“It’ll be really interesting to see what comes out,” says Amy Mainzer, a planetary scientist at the University of Arizona in Tucson who is not involved in DART. “Asteroids have a way of surprising us,” she says, because it’s hard to know a space rock’s precise chemical makeup and internal structure based on observations from Earth. So Dimorphos’ motion post-impact may not exactly match researchers’ expectations.

The DART team will compare data on Dimorphos’ new orbit with their computer simulations to see how close those models were to predicting the asteroid’s actual behavior and tweak them accordingly. “If we can get our models to reproduce what actually happened, then you can use those models to [plan for] other scenarios that might show up in the future” — like the discovery of a real killer asteroid, says DART team member Wendy Caldwell, a mathematician and planetary scientist at Los Alamos National Laboratory.

“No matter what happens,” she says, “we will get information that is valuable to the scientific community and to the planetary defense community.”  More

Humankind is seeing Neptune’s rings in a whole new light thanks to the James Webb Space Telescope.

In an infrared image released September 21, Neptune and its gossamer diadems of dust take on an ethereal glow against the inky backdrop of space. The stunning portrait is a huge improvement over the rings’ previous close-up, which was taken more than 30 years ago.

Unlike the dazzling belts encircling Saturn, Neptune’s rings appear dark and faint in visible light, making them difficult to see from Earth. The last time anyone saw Neptune’s rings was in 1989, when NASA’s Voyager 2 spacecraft, after tearing past the planet, snapped a couple grainy photos from roughly 1 million kilometers away (SN: 8/7/17). In those photos, taken in visible light, the rings appear as thin, concentric arcs.

As Voyager 2 continued to interplanetary space, Neptune’s rings once again went into hiding — until July. That’s when the James Webb Space Telescope, or JWST, turned its sharp, infrared gaze toward the planet from roughly 4.4 billion kilometers away (SN: 7/11/22).

Neptune’s elusive rings appear as thin arcs of light in this 1989 image from the Voyager 2 spacecraft, taken shortly after the probe made its closest approach to the planet. JPL/NASA

Neptune itself appears mostly dark in the new image. That’s because methane gas in the planet’s atmosphere absorbs much of its infrared light. A few bright patches mark where high-altitude methane ice clouds reflect sunlight.

And then there are the ever-elusive rings. “The rings have lots of ice and dust in them, which are extremely reflective in infrared light,” says Stefanie Milam, a planetary scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md., and one of JWST’s project scientists. The enormity of the telescope’s mirror also makes its images extra sharp. “JWST was designed to look at the first stars and galaxies across the universe, so we can really see fine details that we haven’t been able to see before,” Milam says.

Upcoming JWST observations will look at Neptune with other scientific instruments. That should provide new intel on the rings’ composition and dynamics, as well as on how Neptune’s clouds and storms evolve, Milam says. “There’s more to come.”

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A single, doomed moon could clear up a couple of mysteries about Saturn.

This hypothetical missing moon, dubbed Chrysalis, could have helped tilt Saturn over, researchers suggest September 15 in Science. The ensuing orbital chaos might then have led to the moon’s demise, shredding it to form the iconic rings that encircle the planet today.

“We like it because it’s a scenario that explains two or three different things that were previously not thought to be related,” says study coauthor Jack Wisdom, a planetary scientist at MIT. “The rings are related to the tilt, who would ever have guessed that?”

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Saturn’s rings appear surprisingly young, a mere 150 million years or so old (SN: 12/14/17). If the dinosaurs had telescopes, they might have seen a ringless Saturn.  Another mysterious feature of the gas giant is its nearly 27-degree tilt relative to its orbit around the sun. That tilt is too large to have formed when Saturn did or to be the result of collisions knocking the planet over.

Planetary scientists have long suspected that the tilt is related to Neptune, because of a coincidence in timing between the way the two planets move. Saturn’s axis wobbles, or precesses, like a spinning top. Neptune’s entire orbit around the sun also wobbles, like a struggling hula hoop.

The periods of both precessions are almost the same, a phenomenon known as resonance. Scientists theorized that gravity from Saturn’s moons — especially the largest moon, Titan — helped the planetary precessions line up. But some features of Saturn’s internal structure were not known well enough to prove that the two timings were related.

Wisdom and colleagues used precision measurements of Saturn’s gravitational field from the Cassini spacecraft, which plunged into Saturn in 2017 after 13 years orbiting the gas giant, to figure out the details of its internal structure (SN: 9/15/17). Specifically, the team worked out Saturn’s moment of inertia, a measure of how much force is needed to tip the planet over. The team found that the moment of inertia is close to, but not exactly, what it would be if Saturn’s spin were in perfect resonance with Neptune’s orbit.

“We argue that it’s so close, it couldn’t have occurred by chance,” Wisdom says. “That’s where this satellite Chrysalis came in.”

After considering a volley of other explanations, Wisdom and colleagues realized that another smallish moon would have helped Titan bring Saturn and Neptune into resonance by adding its own gravitational tugs. Titan drifted away from Saturn until its orbit synced up with that of Chrysalis. The enhanced gravitational kicks from the larger moon sent the doomed smaller moon on a chaotic dance. Eventually, Chrysalis swooped so close to Saturn that it grazed the giant planet’s cloud tops. Saturn ripped the moon apart, and slowly ground its pieces down into the rings.

Calculations and computer simulations showed that the scenario works, though not all the time. Out of 390 simulated scenarios, only 17 ended with Chrysalis disintegrating to create the rings. Then again, massive, striking rings like Saturn’s are rare, too.

The name Chrysalis came from that spectacular ending: “A chrysalis is a cocoon of a butterfly,” Wisdom says. “The satellite Chrysalis was dormant for 4.5 billion years, presumably. Then suddenly the rings of Saturn emerged from it.”

The story hangs together, says planetary scientist Larry Esposito of the University of Colorado Boulder, who was not involved in the new work. But he’s not entirely convinced. “I think it’s all plausible, but maybe not so likely,” he says. “If Sherlock Holmes is solving a case, even the improbable explanation may be the right one. But I don’t think we’re there yet.” More