The Hubble Space Telescope has observed a swarm of rocks that may have broken off the surface of the asteroid Dimorphos, after the DART probe deliberately crashed into it to try to deflect it, in what was the first test of planetary defense.

The images taken by Hubble indicate that the size of the 37 rocks ejected from the asteroid range from 1 to 6.7 meters in diameter, they move away at a speed of about one kilometer per hour and their total mass corresponds to about 0.1% of the mass of Dimorphos, which is about 160 meters.

The rocks are most likely not shattered pieces of the small asteroid caused by the DART impact, but were scattered across the asteroid’s surface, as seen in the last close-up the spacecraft took just two seconds before impact, when it was only 7 miles from the surface.

It’s not clear how the rocks were lifted from the asteroid’s surface, a possibility that they were part of a plume of ejected material already imaged by Hubble and other observatories, the European Space Agency (ESA) said in a statement.

It’s also possible that a seismic wave from the impact caused the asteroid to shake, as if a bell had been struck with a hammer, dislodging debris from the surface.

asteroid deflection

The probe of the DART mission intentionally crashed into the asteroid Dimorphos on September 26, 2022, about 7 million miles from Earth at the time of impact.

This exercise allowed NASA to train in case an asteroid threatens to hit Earth one day.

The DART impact deflected the Dimorphos’ trajectory. Hubble images show that the collision also released 37 rocks from 1 to more than 7 meters in diameter into the cosmos.

According to a statement, the rocks are slowly moving away from the asteroid, at a speed of about 1 km/h.

At this speed, the European Space Agency’s Hera mission – which should inspect the asteroid in 2026 – will be able to observe the rock cloud.

This image “tells for the first time what happens when you hit an asteroid and what comes out of it.”

The rock scatter indicates that DART has created a crater about 50 meters in diameter on the asteroid.

Scientists will continue to study the trajectory of the rocks to understand “which directions they were ejected.”