NASA craft that diverted space rock also dented it
Collision with NASA spacecraft altered the asteroid Dimorphos’ shape.
When NASA sent its DART spacecraft to slam into the asteroid Dimorphos in 2022, the U.S. space agency demonstrated it was possible to change a celestial object’s trajectory, if needed, to protect the earth. It turns out 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 have said.
“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 coauthor of the study published in the Planetary Science Journal.
“The shape change was so dramatic because of its rubblepile composition,” said JPL navigation engineer and study lead author Shantanu Naidu. “By measuring the pre and postimpact orbit of Dimorphos, we were able to deduce the change in the shape of Dimorphos due to the DART impact.”
The spacecraft collided on September 26, 2022, at about 22,530 kph into Dimorphos, which was about 170 metres wide, roughly 11 million km from the earth.
Dimorphos is a moonlet of Didymos, which is defined as a nearearth asteroid. The DART (Double Asteroid Redirection Test) mission was a proofofprinciple mission using a spacecraft to apply kinetic force to nudge a celestial object that otherwise might be on a collision course with the earth. Dimorphos and Didymos do not pose an actual threat to the earth.
The spacecraft collided on September 26, 2022, at about 22,530 kph into Dimorphos, which was about 170 metres wide, roughly 11 million km from the earth. Didymos has a diameter of about 780 metres.
DART’s collision, which sent rocky debris from the asteroid flying into space, also changed the orbital path that Dimorphos takes around Didymos – making it elliptical instead of circular – and its orbital period, the time it takes to complete a single orbit, the scientists said. It now takes Dimorphos 15 seconds less than before the impact to complete an orbit, they found.
Scientists had previously disclosed that the asteroid’s orbit had changed, with the new study offering the most precise readings yet.
Dr. Chesley said the asteroid’s orbital period continued to decay slowly in the weeks after the impact.
“We believe this is due to the fact that loose debris in the system continues to leak out and carries angular momentum with it, thus necessarily contracting the orbit,” he added. Angular momentum refers to how much a rotating object’s mass is distributed around its axis and how quickly it is spinning.