Collision with NASA spacecraft altered shape of asteroid Dimorphos

When NASA sent its DART spacecraft to slam into the asteroid Dimorphos in 2022, the U.S. space agency demonstrated that it was possible to change a celestial object’s trajectory, if needed, to protect Earth.

When NASA sent its DART spacecraft to slam into the asteroid Dimorphos in 2022, the U.S. space agency demonstrated that it was possible to change a celestial object's trajectory, if needed, to protect Earth. It turns out that this collision changed not only the asteroid's path but its shape as well.

The asteroid, which before the DART encounter looked like a ball that was a bit plump in the waist, now appears to be shaped more like a watermelon - or, technically, a triaxial ellipsoid, scientists said on Tuesday.

"The prevailing understanding is that Dimorphos is a loosely packed agglomeration of debris ranging from dust to gravel to boulders. Thus, its global strength is quite low, allowing deformation much more easily than for a solid monolithic body," said Steve Chesley, a senior research scientist at NASA's Jet Propulsion Laboratory (JPL) in California and a co-author of the study published in the Planetary Science Journal.

"The shape change was so dramatic because of its rubble-pile composition," said JPL navigation engineer and study lead author Shantanu Naidu. "By measuring the pre- and post-impact orbit of Dimorphos, we were able to deduce the change in the shape of Dimorphos due to the DART impact."

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Dimorphos is a moonlet of Didymos, which is defined as a near-Earth asteroid. The DART (Double Asteroid Redirection Test) mission was a proof-of-principle mission using a spacecraft to apply kinetic force to nudge a celestial object that otherwise might be on a collision course with Earth. Dimorphos and Didymos do not pose an actual threat to Earth.

The spacecraft collided on Sept. 26, 2022, at about 14,000 miles per hour (22,530 kph) into Dimorphos, an asteroid that was about 560 feet (170 meters) wide, roughly 6.8 million miles (11 million km) from Earth. Didymos has a diameter of about a half mile (780 meters).