NASA's DART Mission Propels a Swarm of Boulders into Space

 

When a probe collided with a small asteroid last year, the impact not only altered the asteroid's orbit but also catapulted several sizable boulders into space.

In September, NASA directed the DART spacecraft to collide with Dimorphos, a moonlet of the larger asteroid Didymos, as part of a test to assess the efficacy of diverting future Earth-bound asteroids (SN: 10/11/22). Approximately three months after the collision, researchers observed through the Hubble Space Telescope a group of 37 previously unknown objects orbiting the sun alongside the asteroid pair, as reported in the Astrophysical Journal Letters on July 21.

The boulders are likely not fragments that were pulverized from larger rocks during the impact. Instead, simulations indicate that they were probably whole and intact when they were propelled off Dimorphos. The energy from either the collision itself or the seismic waves reverberating inside the moonlet after the impact could have launched these boulders from its surface, which is covered in rubble.

However, planetary astronomer David Jewitt from the University of California, Los Angeles, emphasizes that there is a considerable amount of uncertainty in these simulations.

Based on the brightness of the newly discovered objects, some of which are among the dimmest ever observed by Hubble in our solar system, Jewitt and his colleagues estimate that these boulders could have a width of up to 7 meters. At least 15 of them are larger than 4 meters in size. Collectively, the researchers calculate that these boulders likely have a total weight of just over 5 million kilograms - roughly equivalent to the weight of 300 dump truck loads of gravel.

Continuous observations by the Hubble telescope reveal that, on average, these boulders are drifting away from Dimorphos and Didymos at a speed of approximately 1 kilometer per hour - slightly faster than the escape velocity for the double asteroid system. Therefore, Jewitt explains, the boulders, along with potentially numerous smaller and fainter rocks that Hubble cannot detect, will eventually break away from the asteroid system's orbit and orbit the sun independently.