NASA has published new analysis of its 2022 planetary defense test that suggests the mission slowed down the target asteroids, albeit infinitesimally.
The aerospace agency named its 2022 experiment the Double Asteroid Redirection Test (DART), which readers may remember saw a 570kg spacecraft sent to collide with a 170-metre-wide asteroid named Dimorphos that orbits a larger space rock named Didymos. The aim of the mission was to investigate the feasibility of diverting an asteroid that poses a threat to Earth.
Analysis of the mission found the collision moved Dimorphos closer to Didymos, and reduced the duration of the smaller rock’s orbit. Astroboffins who peered at the asteroids using the Hubble Space Telescope also spotted 37 boulders orbiting Dimorphos after DART struck.
Last Friday, the journal Science Advances published fresh analysis of the DART mission titled “Direct detection of an asteroid’s heliocentric deflection: The Didymos system after DART.”
NASA’s summary of the research reminds us that scientists use the term “momentum enhancement factor” to describe the thrust imparted when one object hits another in space.
“The momentum enhancement factor for DART’s impact was about two, meaning that the debris loss doubled the punch created by the spacecraft alone,” the summary explains before adding “The new study shows the impact ejected so much material from the binary system that it also changed the binary’s orbital period around the Sun by 0.15 seconds.”
Rahil Makadia, the study’s lead author at the University of Illinois Urbana-Champaign, shared another finding: “The change in the binary system’s orbital speed was about 11.7 microns per second, or 1.7 inches per hour,” he said. “Over time, such a small change in an asteroid’s motion can make the difference between a hazardous object hitting or missing our planet.”
“This is a tiny change to the orbit, but given enough time, even a tiny change can grow to a significant deflection,” said Thomas Statler, lead scientist for solar system small bodies at NASA Headquarters in Washington. “The team’s amazingly precise measurement again validates kinetic impact as a technique for defending Earth against asteroid hazards and shows how a binary asteroid might be deflected by impacting just one member of the pair.”
The method used to reach that conclusion is also interesting, as the authors of the paper used observations conducted by volunteer astronomers who recorded 22 stellar occultations between October 2022 and March 2025.
“When combined with years of existing ground-based observations, these stellar occultation observations became key in helping us calculate how DART had changed Didymos’ orbit,” said study co-lead Steve Chesley, a senior research scientist at JPL. “This work is highly weather dependent and often requires travel to remote regions with no guarantee of success. This result would not have been possible without the dedication of dozens of volunteer occultation observers around the world.” ®