NASA’s DART spacecraft, prior to its historic impact on the asteroid Dimorphos in 2022, captured high-resolution images of both Dimorphos and its larger counterpart Didymos.
These images have allowed scientists to decode the intricate history of these near-Earth asteroids and understand the formation of binary asteroid systems, which consist of a primary asteroid with a smaller moonlet orbiting it. Analysis of Didymos’s craters and surface strength suggests it formed around 12.5 million years ago, while Dimorphos is estimated to have formed about 300,000 years ago.
Didymos likely originated in the main asteroid belt between Mars and Jupiter before being pushed into the inner solar system.
Examination of the largest boulders on Didymos and Dimorphos revealed that these asteroids are made up of rocky fragments from the destruction of a parent asteroid.
“These large boulders could not have formed from impacts on the surfaces of Didymos and Dimorphos themselves,” said Maurizio Pajola of the National Institute for Astrophysics (INAF) in Italy. Pajola explained that such impacts would have shattered the asteroids, according a report by Reuters.
Didymos, with a diameter of about 780 meters, and Dimorphos, roughly 170 meters wide, are classified as “rubble pile” asteroids. Their surfaces are strewn with boulders, with the largest on Dimorphos comparable to a school bus and on Didymos as large as a soccer field. Olivier Barnouin from Johns Hopkins University noted that the surfaces of both asteroids are much weaker than loose sand.
The study shows that Dimorphos likely formed from material ejected from Didymos’s equatorial region due to the latter’s faster rotation in the past. Didymos currently rotates once every 2.25 hours. The DART mission, which struck Dimorphos on September 26, 2022, at approximately 14,000 miles per hour, successfully demonstrated the ability to alter an asteroid’s trajectory, although Didymos and Dimorphos pose no immediate threat to Earth.