DART Mission Confirmed to Alter Entire Asteroid System's Solar Orbit
NASA's Double Asteroid Redirection Test (DART) mission, which intentionally impacted the asteroid Dimorphos in 2022, has been confirmed to have altered the orbital path of the entire Didymos-Dimorphos binary system around the sun. This planetary defense test demonstrated the effectiveness of a kinetic impactor in modifying a celestial body's trajectory, a key objective for Earth protection strategies.
Mission Overview
The DART spacecraft, developed by the Johns Hopkins Applied Physics Laboratory for NASA's Planetary Defense Coordination Office, impacted Dimorphos on September 26, 2022. The impact occurred at a speed of approximately 4 miles (6.6 kilometers) per second, or 14,000 mph.
The Didymos-Dimorphos binary asteroid system was selected as a safe testing ground for this experiment. Didymos measures about 2,788 feet (850 meters) across, while its moonlet, Dimorphos, is approximately 560 feet (170 meters) in diameter. Due to Dimorphos' gravitational binding to Didymos, the mission posed no risk of inadvertently redirecting it toward Earth.
Orbital Alterations Confirmed
The primary objective of the DART mission was to shorten Dimorphos' orbit around Didymos. Prior to the impact, Dimorphos orbited Didymos in approximately 11 hours and 55 minutes. The impact successfully reduced this orbital period to 11 hours and 23 minutes, a decrease of 32 minutes. The mission's goal was a minimum reduction of 73 seconds.
New observations, detailed in the journal Science Advances, confirm that the DART impact also altered the binary system's solar orbit. The time required for Didymos and Dimorphos to complete one solar orbit, approximately 770 days, permanently decreased by 0.15 seconds. This adjustment corresponds to a change in the binary system's orbital speed of about 11.7 microns per second, equivalent to 1.7 inches per hour.
This event marks the first documented instance of a human-crafted object altering the path of a celestial body as it orbits the sun.
Role of Ejecta
The impact of the DART spacecraft on Dimorphos released an estimated 35.3 million pounds (16 million kilograms) of debris, known as ejecta. Analysis, led by Rahil Makadia of the University of Illinois Urbana-Champaign and Steve Chesley of NASA's Jet Propulsion Laboratory (JPL), revealed that this ejected material played a significant role in the orbital changes.
The momentum carried away by the ejecta provided an additional thrust, described as a "momentum enhancement factor." For the DART impact, this factor was calculated to be two, meaning the ejecta effectively doubled the momentum transfer from the spacecraft's direct collision to the asteroid system. This additional momentum, transmitted through the gravitational link between Dimorphos and Didymos, contributed to the change in the system's solar orbit.
Measurement and Confirmation
Confirmation of these orbital changes relied on extensive ground-based observations. A critical method involved stellar occultations, where the asteroid system passes in front of a distant star as viewed from Earth. These events provide data on an asteroid's shape, size, position, and trajectory.
Between October 2022 and March 2025, 22 stellar occultations involving the Didymos-Dimorphos system were observed by volunteer astronomers globally. A total of 49 amateur astronomers contributed to this data collection, which was crucial for Makadia and Chesley's team in calculating the precise alterations to the binary system's solar orbit.
The orbital changes also allowed for updated calculations of the asteroids' densities. Didymos has an estimated density of 2,600 kilograms per cubic meter. Dimorphos was found to be less dense than previously thought, at 1,540 kg per cubic meter, a characteristic consistent with a loosely bound "rubble pile." This supports the hypothesis that Dimorphos may have formed from material ejected from Didymos.
Implications for Planetary Defense
The DART mission validates kinetic impact as a viable technique for defending Earth against asteroid hazards. It demonstrated the capability to modify an asteroid's trajectory and showed that impacting only one member of a binary asteroid pair can deflect the entire system. Such an intervention would require sufficient time for detection and planning if a potentially hazardous asteroid were on a collision course with Earth.
Further Research
Ongoing and future missions aim to build upon DART's findings. The European Space Agency's Hera mission is planned to conduct a detailed post-impact survey of Dimorphos. NASA also plans to launch the Near-Earth Object (NEO) Surveyor space telescope after September 2027, with the objective of identifying undiscovered asteroids near Earth's orbital path.