NASA’s crash into an asteroid may have changed its shape

In 2022, when NASA’s $325 million spacecraft crashed into an asteroid called Dimorphos at 14,000 miles per hour, Earth once again erupted in cheers and applause.

NASA’s Double Asteroid Redirection Test (DART) mission deliberately targeted Dimorphos to change its orbit around the larger asteroid Didymos as a sort of dress rehearsal for thwarting a deadly space rock that could one day be heading towards Earth.

The world’s first ever planetary defense experiment was considered a triumph: the asteroid’s orbit shrank by 33 minutes, well above the minimum threshold of 73 seconds.

But what the DART team didn’t realize at the time was how bizarrely Dimorphos reacted to that blow. a new studypublished Monday in Nature Astronomy, has concluded that DART hit Dimorphos so hard that the asteroid changed shape.

Simulations of the impact suggest that the spacecraft’s death did not excavate a normal, bowl-shaped crater. Instead, it left something that looks like a dent. And although the artificial impact blasted millions of tons of rock into space, much of it splashed back onto the sides like huge tidal waves. It widened Dimorphos, transforming it from a squat ball into a flat-topped oval, like an M&M candy.

The fact that the asteroid behaved like a liquid is due to its peculiar composition. It’s not a solid, continuous rock, but more of a “pile of sand,” he said Sabina Raducan, a planetary scientist at the University of Bern in Switzerland and lead author of the study. And a low-density asteroid barely held together by its own gravity would never react in a simple way if a spacecraft the size of a van flew into its face.

Dimorphos’ response is “completely outside the realm of physics as we understand it in our daily lives,” he said Christina Thomas, the leader of the mission’s observational working group at Northern Arizona University, who was not involved in the study. And “this has overarching implications for planetary defense.”

DART showed that a small spacecraft can deflect an asteroid. But the study indicates that crashing a similarly disjointed space rock too forcefully risks fragmenting it, which in a true asteroid emergency could create multiple Earth-bound asteroids.

Planetary defense clearly works as a concept. “We know we can do it,” he said Federica Spoto, an asteroid dynamics researcher at the Center for Astrophysics, Harvard and Smithsonian, who was not involved in the new study. “But we have to do it right.”

Dimorphos was chosen as a target for DART for numerous reasons. One of the most important was its size: at 170 meters across, it is just the right size of a common variant of a stony asteroid that could easily destroy a city.

Because it is so small and therefore difficult to observe from Earth, little was known about Dimorphos before DART glimpsed it up close during the spacecraft’s terminal approach. But many scientists suspected it was a pile of rubble, a collection of closely spaced boulders.

The handful of space missions that have visited asteroids of similar size – even those with different geological compositions – also showed no correlation. This makes them behave strangely. For example, when NASA’s OSIRIS-REx spacecraft briefly touched down on the surface of the debris-like asteroid Bennu to steal a sample, it sank almost completely into it, as if it were dump into a plastic ball pit.

That DART’s collision knocked Dimorphos back so clearly demonstrated that deflecting these types of asteroids can be successful, even if their properties are largely unknown beforehand.

But early observations made by ground-based telescopes, space-based observatories, and the LICIACube (a small satellite that rode with the DART spacecraft) hinted that Dimorphos responded to this act of interplanetary vandalism with unexpected drama.

“A lot An amount of material was thrown away,” said Dr. Thomas. Dimorphos was quickly enveloped by one swarm of boulders and was followed by a 20,000-mile-long comet-like tail that lasted for months.

What other surprises does Dimorphos have in store? HeraA European Space Agency mission will launch in October and arrive in Dimorphos in late 2026 to explore the asteroid wreckage.

But Dr. Raducan was impatient and decided instead to predict what Hera might discover. Her team ran simulations of the impact, hoping to see which virtual outcome best fit Dimorphos’ fleeting observations after the impact. The lack of a classic crater and a transformed asteroid is not what most astronomers expected.

Like his previously explored asteroid siblings, Dimorphos reacted in an unexpected way when angrily prodded by a robot. That means if the world needs saving from an incoming mess, no assumptions can be made.

“We need more space missions to asteroids,” said Dr. Raducan. “Just because we hit one asteroid doesn’t mean they will all behave the same.”