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At an APS meeting in Chicago, Stickle coolly explained how smashing a spacecraft into an asteroid could someday save Earth — and, after last year’s test, what comes next.
By Liz Boatman | August 10, 2023
This image, taken by the LICIACube satellite, shows the plumes of debris ejected from the Dimorphos asteroid after it was struck by the DART spacecraft. Each rectangle represents a different level of contrast.
In September 2022, space enthusiasts around the world played a 39-second video on repeat — the last moments of NASA’s DART spacecraft before it collided with the asteroid Dimorphos, a “moonlet” of the larger asteroid Didymos.
In the eerie, silent footage, the spacecraft’s approach looks slow. It wasn’t. The force of the impact “was like a golf cart hitting a pyramid at 15,000 miles per hour,” says Angela Stickle, a planetary geologist at the Johns Hopkins Applied Physics Laboratory (APL), who led the mission’s modeling efforts.
In June, Stickle presented the results of her team’s work at the 23rd Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter, held in Chicago.
The mission was a success: Dimorphos’s orbit around Didymos was altered by 33 minutes. It was a test run for the theory that smashing a spacecraft into an asteroid could, in the future, shift its trajectory enough to keep it from colliding with Earth. In other words, DART, short for Double Asteroid Redirection Test, was the world’s first test of planetary defense.
Key to this feat? Modeling. Stickle says one of the most important findings is that the code her team uses to model impacts, called “shock hydrocodes,” gives similar results as other codes developed by researchers around the world.
“A lot of these have grown up independently, but we’re finding that they all work the same for these kinds of problems,” she says. “We can utilize a broader community to do some of this work.” Planet-wide collaboration for planet-wide defense.
Stickle’s interest in impact physics began as an undergrad at the University of Washington. She chose it for its aerospace program, but when she took a geology class, she got hooked on rocks. “I basically fell in love with [geology],” she says.
After an internship at the Jet Propulsion Laboratory in California, she knew she was interested in planetary geology. She enrolled in graduate school at Brown University, where she got her first taste of impact physics. “My research was both in experiments and in simulations,” she says. “A lot of what I was interested in was how things break.”
Eventually, she landed at the Johns Hopkins APL. One day at lunch, she and a few colleagues were “tossing ideas around,” discussing whether it would be possible to crash a spacecraft into an asteroid and redirect its orbit. The idea grew into a mission concept study, “which essentially means we had a little bit of money to look at it and see if it was feasible,” Stickle says.
By 2015, the concept had gained momentum, and the DART mission was born. Given her work on the mission concept study, Stickle was tasked with leading the impact modeling working group.
She brought together collaborators from around the world to carry out a range of studies, “to understand what we could expect from DART prior to impact.” It was tricky work. “The processes that we’re talking about are big,” she says. “Constructing an experiment that can faithfully represent that type of process — it’s not always easy.”
Finally, in November 2021, the DART craft was launched into space aboard a SpaceX Falcon 9 rocket.
On Sept. 26, 2022 — nearly a year later, after the spacecraft had traveled some 7 million miles — Stickle’s team stood by and braced for impact. “It was incredible. We had the livestream on that NASA was broadcasting,” she recalls.
They watched the feed from DART’s camera as the spacecraft raced toward Dimorphos. The asteroid, at first a distant gray speck, grew closer and closer until its rocky surface filled the screen. Then, impact — the feed stopped.
“I get goosebumps still, every time I watch those videos,” says Stickle.
From a safe distance away, LICIACube, a tiny “CubeSat” satellite developed by the Italian Space Agency that had flown with DART across the solar system, snapped post-impact images. Those images revealed that the impact was powerful enough to spew debris, including boulder-sized rocks, in every direction. “The ejecta from the impact crater was a little bit of a surprise,” Stickle says.
Since then, Stickle’s team has been working with the post-impact data, using simulations to probe the asteroid’s structure. Next, they’ll apply what they learn to new impact studies. Their work could shape the development of technologies that could save Earth from rogue asteroids.
Objects already regularly collide with Earth. Friction in the atmosphere usually burns up smaller objects, creating the vibrant displays we call “shooting stars” and meteor showers, but Earth’s surface has also been scarred by more devastating collisions. Some have left craters large enough to be seen from space, like the Chicxulub crater on Mexico’s Yucatán Peninsula, thought to be the site of the asteroid impact that killed off the last dinosaurs.
Should we be concerned about an impact like that in our lifetimes? “The odds are very, very low,” says Stickle. “Part of the planetary defense program is to find all the potential threats. NASA has a lot of telescopes on the Earth and in space looking for objects that could be a threat.”
“We have not found any that are on a course to collide with the Earth in the next hundred years,” she says.
Stickle says NASA will soon launch the Near-Earth Object Surveyor Mission, to look for smaller objects that could still pose a threat. And NASA isn’t the only entity involved in trying to keep Earth’s inhabitants safe from asteroids. The European Space Agency is preparing the Hera mission, to rendezvous with Dimorphos and Didymos. And the United Nations runs international committees on the topic that include countries from all over the world.
Stickle says it’s a good thing the United States isn’t “alone” in this effort to keep the planet safe from space impacts. “We definitely need the world to be invested in this sort of technology.”
Liz Boatman is a staff writer for APS News.
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