Before DART smashed into it on September 26, it took Dimorphos 11 hours and 55 minutes to circle its larger parent asteroid, Didymos. Astronomers have been using telescopes on Earth to measure how much that time has changed. The data shows that the impact from the small spacecraft shortened Dimorphos’ orbit around Didymos by 32 minutes, with a margin of uncertainty of about plus or minus 2 minutes. Shortening an asteroid system’s trajectory like this could help us deflect a massive space rock if it were to threaten Earth.
“All of us have a responsibility to protect our home planet. After all, it’s the only one we have,” said NASA Administrator Bill Nelson in a press release. “This mission shows that NASA is trying to be ready for whatever the universe throws at us. NASA has proven we are serious as a defender of the planet.”
Before the collision, the agency defined the minimum successful orbit period change of Dimorphos as change of 73 seconds or more. This early data shows DART surpassed this minimum benchmark by more than 25 times. Data is still being collected by ground-based telescopes from around the world and radar facilities at NASA Jet Propulsion Laboratory’s Goldstone facility in California and the National Science Foundation’s Green Bank Observatory in West Virginia.
According to NASA, the focus is now shifting toward measuring the efficiency of momentum transfer from DART’s roughly 14,000-mile per hour collision with Dimorphos. There will be further analysis of the asteroidal rock that was launched into space after impact called ejecta. The recoil from the blast enhanced DART’s push against the asteroid; NASA experts described it is a little like a jet of air streaming out of a balloon, sending it in the opposite direction.
More information on of the asteroid’s physical properties will be needed to better understand how much impact the ejecta had. To project the mass and shape of the asteroid, astronomer will continue to study imagery of Dimorphos from DART’s terminal approach and from the Light Italian CubeSat for Imaging of Asteroids, provided by the Italian Space Agency.
“DART has given us some fascinating data about both asteroid properties and the effectiveness of a kinetic impactor as a planetary defense technology,” said Nancy Chabot, the project’s coordination lead from the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, in a press release. “The DART team is continuing to work on this rich dataset to fully understand this first planetary defense test of asteroid deflection.”
During the media briefing, Chabot also stressed that early detection of threatening asteroids will be key in employing kinetic impactor techniques in the future. “This was a 4 percent change in the orbital period of Dimorphos around Didymos. It just gave it a small nudge,” she said. “If you wanted to do this in the future, it would potentially work, but you’d want to do this years in advance. Warning time is really key here in order to enable this sort of asteroid deflection to be used as part of a larger planetary defense strategy.”
The $325-million NASA test began with DART’s launch in November 2021. On September 26th, the car-sized spacecraft made kinetic impact with Dimorphos at 14,000 mph and around 7 million miles away from Earth. The goal was for the spacecraft to nudge the 525-foot-wide asteroid into a tighter orbit around its parent rock. Dimorphos is a smaller companion to the 2,500-foot-wide Didymos, and is a moonlet orbiting the larger body at at less than a mile apart. The two make up a binary asteroid system, and were partially selected because there is zero chance that either object or their ejecta would ever threaten Earth, according to NASA.