Scientists from NASA’s Jet Propulsion Laboratory (JPL) have confirmed that when the agency’s Double Asteroid Redirection Test (DART) mission intentionally collided with the asteroid moonlet Dimorphos in September 2020, the collision permanently altered the object’s orbit around the sun.
Because Dimorphos is gravitationally locked to the much larger asteroid Didymos, the impact also altered its orbit around the sun. Dimorphos’ orbit around its asteroid companion was also changed by the impact.
Although there was no threat of either asteroid impacting Earth before or after the DART impact, NASA said the confirmation of the orbital changes confirms the agency’s ability to deflect a potentially hazardous object in space off of its current course.
NASA Says Its DART Mission’s Impact Altered a Binary Asteroid System’s Orbit
According to a statement announcing the confirmation, DART’s planned impact with Dimorphos changed the object’s trajectory and ejected a massive cloud of rocky debris into space. This ejection altered the shape of the 560-foot-wide asteroid and added to the overall orbital change.
“Because the debris carried its own momentum away from the asteroid, it gave Dimorphos an explosive thrust — what scientists call the momentum enhancement factor,” the research team explained, adding that more debris gives this enhancement more ‘oomph.’
A closer analysis of the ejected debris concluded that the momentum enhancement factor for the ejected debris caused by DART’s impact was about two. The research team said this result means the Newtonian reaction from the ejected debris “doubled the punch” of the spacecraft’s energy transfer during impact.
Although the overall effects of the impact and the ejected debris momentum enhancement were relatively small, the team’s analysis did confirm earlier observations suggesting that Dimorphos’ orbital period around its larger partner Didymos had shortened by about 33 minutes per orbit. The data also confirmed that the orbit of the binary asteroids around the Sun was altered by 0.15 seconds.
“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, the study’s lead author at the University of Illinois Urbana-Champaign
Such changes are relatively small on a cosmic scale. However, Makadia noted, even a small change in an asteroid’s motion “can make the difference between a hazardous object hitting or missing our planet.”
NASA Near Earth Object Surveyor Purposely Built for Planetary Defense
When discussing the implications of their findings, the JPL team noted that before their study, there were no scientifically verified incidents of a human-made object altering the orbit of a natural object in space. For example, although Didymos was not a threat when it was first detected, the researchers said DATT changing its orbital speed underscores the role of spacecraft as “kinetic impactors” for planetary defense against hazardous space objects found to be on a collision course with Earth.
“Over time, such a small change in an asteroid’s motion can make the difference between a hazardous object hitting or missing our planet,” Makadia explained.
A key component of NASA’s planetary defense plan is the Near-Earth Object (NEO) Surveyor mission. According to the JL team, NEO is the first next-generation space survey telescope built exclusively for planetary defense. Along with characterizing bright objects spotted by other observatories, NEO will be tasked with some of the hardest-to-find near-Earth objects, including dark asteroids and comets that can evade detection since they don’t reflect much visible light.
When discussing the role of kinetic impactors on planetary defense after an object is located and determined to be on a collision course with Earth, the research team said the DART mission offered direct support for the sci-fi-sounding approach.
“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,” Stater explained.
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.