Nearly a year ago, NASA’s DART mission collided with the asteroid Dimorphos, the moon of the larger asteroid Didymos, to see if it was possible to move it and thereby protect Earth from a future impact.
The goal of NASA’s DART mission was to put the asteroid in a different orbit, and the change was successful: the asteroid moved much further than expected. New research suggests that the orbit continued to change inexplicably for a month after the impact.
DART is a planetary defense system known as a kinetic impactor. It is designed to ram a celestial body at high speed; The exchange of momentum changes the asteroid’s orbit. If the asteroid were on a collision course with Earth, this could move the object to a safer path. The change is usually small, but with enough time it can be enough to be safe.
Dimorphos posed no danger to us. It was chosen because astronomers knew how long it took to orbit Didymos. DART showed that the impact can change an asteroid’s speed, and Dimorphos actually moved to a smaller orbit. The goal was to reduce his playing time by seven minutes, but the impact actually reduced him by 33 minutes, at least initially. Somehow the asteroid lost momentum over time.
A group of high school students from Thacher School conducted pre-impact observations of the asteroid through November 6, 2022. Using the school’s observatory’s 0.7-meter telescope, they measured Dimorphos’ period and found that it continued to increase in the days following the impact, becoming higher than the official reading immediately after the collision.
“The number we got was slightly higher, a change of 34 minutes,” said Dr. Jonathan Swift, professor and director of the observatory, told New Scientist. “It was incoherent on an unpleasant level.”
The behavior wasn’t expected, but to be honest, it’s the first time humanity has literally moved a celestial body. The impact is believed to have created a crater tens of meters across, which is enormous for a body only 160 meters across.
The impact ejected a large amount of material, including many rocks, into orbit. It’s possible that some of this material found its way back to Dimorphos, slowing it down even further. The system is complex. Now it’s like two billiard balls colliding.
“When you hit a pile of debris with a spacecraft, a large amount of material is thrown out and flies away from the object.” This is what we see in our first images after the impact. This ejected material carries momentum. The change in period we observed is the result not only of the momentum transfer of the impacting spacecraft, but also of the additional momentum due to the movement of the ejected material,” explains Dr. Cristina Thomas of the University of Northern Arizona, in a previous interview with IFLScience.
The European Space Agency’s Hera mission will reach the asteroids in late 2026 and provide further data on the collision and its consequences. Currently it looks like the orbit has stabilized. The budding researchers presented their work in June at the American Astronomical Society in Albuquerque and in a paper accepted for publication in Research Notes of the American Astronomical Society.
REFERENCE
An asteroid hit by a NASA spacecraft happened unexpectedly
Photo: NASA/Johns Hopkins, APL/Steve Gribben
