April 24, 2024

“Surprising” discovery: 37 swarming boulders spotted near asteroid hit by NASA spacecraft last year

A recent experiment gave NASA scientists a closer look at how trying to deflect or destroy asteroids approaching Earth could result in more projectiles.

Asteroids are “a real collision hazard for Earth,” according to NASA, who noted in a recent press release that an asteroid measuring miles across hit the planet billions of years ago and caused a mass extinction event that wiped out dinosaurs and other forms of life. To combat this threat, scientists have studied how to knock an approaching Earth asteroid off course.

The result was DART 2022, or the Double Asteroid Redirect Test. The test was conducted on September 26, 2022, and the test half-ton spacecraft smashed into an asteroid at about 14,000 miles per hour, and the results were monitored with the Hubble Space Telescope, a large telescope in outer space that orbits the Earth and takes sharp images of objects in outer space. The trajectory of the orbit of the asteroid around the larger asteroid that it circled around changed slightly as a result of the test.

Scientists were surprised to see several dozen boulders ejected from the asteroid after it was hit, which NASA said in a news release “could mean that an asteroid approaching Earth could be the result of a cluster of threatening boulders.”

The image of the asteroid, with a bluish dust tail, as photographed by the Hubble telescope…. The highlighted blue dots, marked with white circles, show the boulders knocked off the asteroid in the DART test.

NASA, ESA, David Jewitt (UCLA)

Using the Hubble telescope, the scientists found that the 37 boulders flying from the asteroid ranged in size from just 3 feet across to 22 feet across. The boulders are not debris from the asteroid itself, but were likely already scattered across the asteroid’s surface, according to photos taken by the spacecraft just seconds before the collision. The boulders have about the same mass as 0.1% of the asteroid, and are moving away from the asteroid at about half a mile per hour.

David Jewitt, a planetary scientist at the University of California at Los Angeles who used the Hubble telescope to track changes in the asteroid before and after the DART test, said the boulders are “some of the faintest objects ever imaged within our solar system.”

“This is an amazing observation – much better than I expected. We see a cloud of boulders carrying mass and energy from the impact target. The number, sizes and shapes of the boulders are consistent with those after they were removed from the surface of Dimorphos by the impact,” Jewitt said in a NASA news release. “This tells us for the first time what happens when you hit an asteroid and you see material coming out to the largest sizes.”

Jewitt said the impact probably shook off 2% of the boulders on the asteroid’s surface. More information will be collected by the European Space Agency’s Hera spacecraft, which will arrive at the asteroid in late 2026 and conduct a detailed post-impact study of the area. The boulder cloud is expected to still be dispersing when the craft arrives, Jewitt said.

This is the last complete image of the asteroid Dimorphos, as seen by NASA’s DART impactor spacecraft two seconds before impact.


The boulders “are like a swarm of bees that are expanding very slowly and will spread along the (asteroid’s) orbit around the sun,” Jewitt said.

Scientists are also keen to see exactly how the boulders were ejected from the asteroid’s surface: They could be part of a plume taken by the Hubble and other observatories, or a seismic wave from the impact of the DART spacecraft could have vibrated through the asteroid and shaken the surface rubble loose. Comments will continue to try to determine what happened, and trace the path of the boulders.

“If we follow the boulders in future Hubble observations, we may have enough data to pinpoint the exact paths of the boulders. And then we’ll see the directions they were sent from the surface,” Jewitt said.

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