Data obtained by NASA’s Double Asteroid Redirection Test (DART) investigation team over the last two weeks show that the spacecraft’s kinetic impact with its target asteroid, Dimorphos, successfully altered the asteroid’s orbit. This is the first time humanity has purposely changed the motion of a celestial object, as well as the first full-scale demonstration of asteroid deflection technology.
“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. “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. This is a watershed moment for planetary defense and all of humanity, demonstrating commitment from NASA’s exceptional team and partners from around the world.”
Dimorphos took 11 hours and 55 minutes to orbit its larger parent asteroid, Didymos, prior to DART’s impact. Since DART’s intentional collision with Dimorphos on September 26, astronomers have been measuring how much time has passed using telescopes on Earth. The investigation team has now confirmed that Dimorphos’ orbit around Didymos was altered by the spacecraft’s impact, shortening the 11 hour and 55 minute orbit to 11 hours and 23 minutes. This measurement has a margin of uncertainty of approximately 2 minutes.
Before its encounter, NASA had defined a minimum successful orbit period change of Dimorphos as change of 73 seconds or more. This early data show DART surpassed this minimum benchmark by more than 25 times.
“This result is one important step toward understanding the full effect of DART’s impact with its target asteroid” said Lori Glaze, director of NASA’s Planetary Science Division at NASA Headquarters in Washington. “As new data come in each day, astronomers will be able to better assess whether, and how, a mission like DART could be used in the future to help protect Earth from a collision with an asteroid if we ever discover one headed our way.”
The team is still collecting data from ground-based observatories around the world, as well as radar facilities at NASA’s Jet Propulsion Laboratory’s Goldstone planetary radar in California and the National Science Foundation’s Green Bank Observatory in West Virginia. They are regularly updating the period measurement to improve its precision.
The main focus is now on determining the efficiency of momentum transfer from DART’s 14,000-mile (22,530-kilometer) per hour collision with its target. This includes additional analysis of the “ejecta,” or the many tons of asteroidal rock displaced and launched into space by the impact. The push that DART made against Dimorphos was significantly helped by the recoil from this explosion of debris, much like how a balloon is propelled in the opposite direction by a jet of air.
More information on the asteroid’s physical properties, such as the characteristics of its surface and how strong or weak it is, is required to successfully understand the effect of the recoil from the ejecta. These issues are still being investigated.
“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 DART coordination lead from the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland. “The DART team is continuing to work on this rich dataset to fully understand this first planetary defense test of asteroid deflection.”
Neither Dimorphos nor Didymos poses any hazard to Earth before or after DART’s controlled collision with Dimorphos.