Almost a year ago, NASA’s DART mission hit the asteroid Dimorphos, which orbits a larger asteroid, Didymos. The goal was to move it out of orbit, being the first attempt to change the trajectory of such a cosmic object in the scenario where it would be a threat to Earth. The mission was a success, but a group of students from an American high school discovered a strange anomaly in the behavior of the asteroid hit by NASA.
The asteroid hit by NASA in 2022 is behaving strangely
In September 2022, NASA’s DART spacecraft voluntarily collided with the asteroid Dimorphos, 6.8 million kilometers from Earth, orbiting another larger asteroid, Didymos.
This was the space agency’s first “planetary defense test,” done to see if humanity could move a larger celestial body if it were to head toward Earth, threatening life on our planet.
The mission was a success, and the asteroid moved out of its orbit even more than expected. Even if small, the difference can guarantee that a future asteroid dangerous to Earth could be diverted from its path towards us.
The impact is estimated to have created a crater tens of meters in diameter, a huge size compared to the size of the 160 meter long spacecraft.
Dimorphos posed no danger to Earthlings, but it was chosen because astronomers already knew how long it took the asteroid to orbit Didymos, and the collision shortened its orbit by 33 minutes. Much more than NASA’s original goal of shortening it by 7 minutes.
What happens to Dimorphos, the discovery made by a group of high school students
On the other hand, NASA and astronomers expected Dimorphos’ speed and orbit to return to initial values shortly after the impact.
But a group of high school students at the Thacher School in Ojai, California, discovered something unexpected: The asteroid’s orbit continued to change, shortening even a month after the collision with DART. The student group made observations of the asteroid before the September 2022 impact until November 6, 2022.
Using the telescope in the school’s astronomical observatory, they measured the period of Dimorphos—in other words, how long it takes to make a complete revolution around Didymos—and found that it continued to increase steadily, becoming larger than measurements announced by NASA immediately after collision.
“The result we got was higher, the period change being 34 minutes. It was contradictory on a downright uncomfortable level,” Dr Jonathan Swift, professor and director of the school’s observatory, told New Scientist.
Even though NASA had announced a possible margin of error of plus or minus 2 minutes in calculating the new orbit generated by the impact, the results the high school students reached are surprising, because no one anticipated that Dimorphos would continue to slow down.
Some experts believe that the collision also resulted in the scattering of a large amount of material, including many boulders, into orbit.
Some of these may have fallen back on Dimorphos, further reducing his speed and thus shortening his period further. It is, however, a very complex process, and not about two balls colliding in a pool or snooker game.
However, the European Space Agency’s Hera Mission will reach the asteroid towards the end of 2026 and provide much more information about the collision and its aftermath. At present, however, it appears that Dimorphos’ orbit has stabilized.