The intentional impact of the NASA DART mission to divert the path of the Dimorphos asteroid in September 2022 has caused an unintended effect: a space "shrapnel cloud".
At the time, NASA's goal was to assess whether an impactor strategy could be used to protect Earth in the event an asteroid headed toward our planet.
A new study led by UCLA astronomer David Jewitt has found that the collision launched a cloud of rocks from its surface. And, as the article points out, smaller rocks flying into space could create their own problems.
"The rock swarm is like a cloud of shrapnel expanding from a hand grenade," Jewitt, the study's lead author and a UCLA professor of Earth and planetary sciences, said in a statement. "Because those big rocks basically share the speed of the target asteroid, they are capable of doing their own damage."
Jewitt said that given the high velocity of a typical impact, a 15-foot (about 4.5-meter) rock hitting Earth would have as much energy as the atomic bomb dropped on Hiroshima.
Fortunately, neither Dimorphos nor the rock swarm have ever posed any danger to Earth. NASA chose Dimorphos because it was about 9 million kilometers from Earth and less than 200 meters across, close enough to be of interest, and small enough, engineers reasoned, that the DART mission would be capable of changing the asteroid trajectory.
When it crashed into Dimorphos at 20,000 kilometers per hour, DART reduced Dimorphos's orbit around its twin asteroid, Didymos, by a few millimeters per second. But, according to images taken by NASA's Hubble Space Telescope, the collision also shook 37 rocks, each 1 to 7 meters wide. None of the rocks are on track to hit Earth, but if debris from an asteroid's future deflection were to reach our planet, Jewitt said, it would strike at the same speed the asteroid was traveling, fast enough to cause tremendous damage. .
The research, published in the Astrophysical Journal Letters, found that the rocks were likely torn from the surface by the impact. A close-up photograph taken by DART just two seconds before the collision shows a similar number of rocks on the asteroid's surface, and of similar sizes and shapes, to those imaged by the Hubble telescope.
The boulders the scientists studied, among the faintest objects ever seen within the solar system, can be observed in detail thanks to the powerful Hubble telescope.
"If we follow the rocks in future Hubble observations, we may have enough data to pin down the precise trajectories of the rocks," Jewitt said. "And then we'll see what directions they were thrown from the surface and find out exactly how they were ejected."
The European Space Agency's HERA spacecraft will have the opportunity to collect more data on the rocks when it returns to Dimorphos in 2026 to study the DART results in more detail. Findings from that mission will inform future planetary defense strategies and technologies, Jewitt said.
