Asteroid Deflection Test Resulted in Unexpected Boulder Ejection

In late 2022, NASA's Double Asteroid Redirection Test (DART) was conducted as a proof of concept for altering the trajectory of an asteroid that could potentially approach Earth.

The spacecraft collided with Dimorphos, the moonlet of asteroid Didymos, at approximately 14,000 mph, resulting in a significant change to the moonlet's orbit.

Three years after the event, astronomers observed additional effects from the collision. According to a paper published in the Planetary Science Journal, a research team led by the University of Maryland determined that the DART impact caused the ejection of numerous boulders, some of which carried more than three times the energy of the spacecraft.

"We succeeded in deflecting an asteroid, moving it from its orbit," said lead author and UMD research scientist Tony Farnham. "Our research shows that while the direct impact of the DART spacecraft caused this change, the boulders ejected gave an additional kick that was almost as big."

The researchers noted that impacting an asteroid with a spacecraft can initiate a sequence of events that should be considered in future mission planning.

"That additional factor changes the physics we need to consider when planning these types of missions," Farnham added.

Images captured by LICIACube, a small spacecraft developed by the Italian Space Agency and positioned near the impact site, enabled astronomers to track 104 boulders ranging from 0.6 to 11.8 feet in radius as they moved away from Dimorphos.

The researchers observed a specific distribution pattern among the ejected boulders.

"We saw that the boulders weren't scattered randomly in space," Farnham explained. "Instead, they were clustered in two pretty distinct groups, with an absence of material elsewhere, which means that something unknown is at work here."

The team suggests that DART's solar panels likely struck two large boulders, named Atabaque and Bodhran, on the asteroid before the main body of the spacecraft made contact, as described by second author and UMD astronomy professor Jessica Sunshine.

Sunshine added that DART encountered a surface with significant rocky features, resulting in complex and filamentary ejecta patterns.

The European Space Agency's Hera mission, scheduled to visit the asteroid system next year, is expected to provide further observations of the impact site.

The research team aims to use new data to inform future asteroid deflection missions.

"If an asteroid was tumbling toward us, and we knew we had to move it a specific amount to prevent it from hitting Earth, then all these subtleties become very, very important," Sunshine explained.

"You can think of it as a cosmic pool game," she added. "We might miss the pocket if we don't consider all the variables."

• More on DART: Debris From When NASA Smashed Asteroid Appears to Be Headed Back Toward Earth