NASA's asteroid-smashing DART spacecraft hit so hard, it changed its target space rocks' orbit around the sun.

In 2022, NASA's Double Asteroid Redirection Test (DART) mission deliberately slammed into the asteroid Dimorphos, which orbits a larger asteroid named Didymos. Now, scientists have confirmed that not only did DART alter Dimorphos' orbit around its binary companion, but it also altered the whole binary system's orbit around the sun.

"The change in the binary system's orbital speed was about 11.7 microns per second, or 1.7 inches per hour," said Rahil Makadia of the University of Illinois Urbana-Champaign in a statement. "Over time, such a small change in an asteroid's motion can make the difference between a hazardous object hitting or missing our planet."

The objective of DART was to see whether a kinetic impactor — in this case, the DART spacecraft — could deflect an asteroid and prove that if a similarly sized asteroid were on a collision course with Earth, we could knock it out of the way.

The Didymos–Dimorphos double asteroid system was a safe place to practice this. Didymos is the larger asteroid, about 2,788 feet (850 meters) across, and the smaller 560-foot (170-meter) asteroid Dimorphos orbits around Didymos. Because astronomers had previously measured Dimorphos' orbital period and radius precisely, any deflection caused by the impact would be clear to measure as well. Plus, because Dimorphos is gravitationally bound to Didymos, the DART impact could not inadvertently knock it towards Earth.

The DART impact took place on September 26, 2022, with the spacecraft impacting at 4 miles (6.6 kilometers) per second. It knocked Dimorphos enough that its orbital period around Didymos shortened from 11 hours and 55 minutes to 11 hours and 23 minutes. Prior to impact, the aim had been to shove Dimorphos such that its orbital period reduced by a minimum of just 73 seconds, meaning the mission was a tremendous success.

New analysis of the data, led by Makadia and Steve Chesley of NASA's Jet Propulsion Laboratory (JPL), has shown that DART's effort to push Dimorphos received a helping hand from the cloud of debris, called ejecta, that it sprayed into space as it excavated a fresh new crater.

As this ejecta cloud raced away from Dimorphos, it also carried away momentum. And, as momentum is always conserved, this gave Dimorphos an added push. Scientists call this extra push the "momentum enhancement factor," and in the case of Dimorphos and the DART impact, the momentum enhancement factor had a value of two. This means that the loss of the ejecta doubled the thrust imparted on Dimorphos by the initial DART impact.

Source: www.space.com

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