“NASA’s Double Asteroid Redirection Test (DART) mission hasn’t just deflected an asteroid moonlet, it’s also given humankind a much deeper understanding of the geophysics at play during the formation and evolution of asteroids. That’s the most recent result published by a team led by the University of Maryland.”.
Derek Richardson is an astronomy professor at UMD and a lead investigator for the DART mission. “Most of our original pre-impact predictions about how DART would change the way Didymos and its moon move in space were pretty much spot on,” Richardson said. “But there are some surprising results in there that work to fill in our wider picture of how asteroids and other small bodies develop and change over time.”
The findings, published in the Planetary Science Journal on August 23, 2024, showed that Dimorphos, once oblate like a hamburger, tended to take a more prolate shape, similar to a football, in the aftermath. The transformation goes in a way that contradicts previous assumptions about how so-called moons like this piled material and became elongated bodies.
According to Richardson, the shape change in Dimorphos due to the impact probably disturbed its interaction with the parent asteroid Didymos. Though the DART collided merely on the moon, the gravitational link between the two bodies and the debris thrown out by the impact perturbed the equilibrium and shortened the orbiting of Dimorphos around Didymos. More interestingly, no alteration of shape was observed concerning Didymos, proving that it is firm and rigid.
The results are of high importance for all future missions, especially those planned for the Didymos system in October 2024 by the European Space Agency. The findings show that Dimorphos might be in a “tumbling” state, causing chaotically unpredictable rotation. This is likely to influence future missions of landing and research.
The DART mission has also offered clear images and information, both through its camera and the Italian robotic observer, LICIACube. It was found from those images that Didymos’ surface is about 12.5 million years old, but Dimorphos’ surface varies from 90,000 to 300,000 years old.
Further observations confirmed that Didymos is a “pile of rubble,” made up of large boulders which originated from some past catastrophic event that was likely to have occurred in the ancient past. Fractures on Dimorphos’ boulders that were caused by thermal fatigue due to solar radiation suggested that, on similar missions, additions from future kinetic impactors might be added to the ejected mass during such missions for useful instigation.
The study also noted that the eclipses may be cooling the rocks over Dimorphos, affecting their thermal fatigue. This peculiar binary asteroid system provides one of the few cases where studies will be done on these phenomena since other well-studied asteroids and comets are not present as a couple in blocking light.
They found it had a surface strength much weaker than the dry sand on Earth, which contributed to why DART had such a big impact on Dimorphos’s orbit. This will be very important information for planetary defense design.
With the European Space Agency’s Hera mission expected to arrive in the Didymos system in late 2026, that will give scientists the closest look yet at the internal properties of both asteroids. “DART provided insight about complex gravitational physics that cannot be obtained in a laboratory,” Richardson said. “All of this work helps in getting our mission ready to protect Earth from a real threat”.
This was the aim of the research by NASA, the U.S. National Science Foundation, and a group of international space agencies and research organizations. The findings underline the need to move forward in the study and research of near-Earth asteroids—as long as mankind understands and takes over potential threats approaching the Earth.