NASA’s DART spacecraft successfully changed the trajectory of the asteroid moonlet Dimorphos in September 2022, shortening its orbit around its larger companion, Didymos, by 33 minutes. This landmark mission marked humanity’s first successful test of a planetary defense technique, demonstrating that a kinetic impactor can alter an asteroid's path in space. The collision happened approximately 11 million kilometers (6.8 million miles) from Earth.
Historic Asteroid Impact Success
The Double Asteroid Redirection Test (DART) mission involved intentionally crashing a spacecraft into Dimorphos, a body roughly 160 meters (525 feet) in diameter. Dimorphos orbits the larger asteroid Didymos, which measures about 780 meters (2,560 feet) across. Before the impact, Dimorphos completed one orbit around Didymos every 11 hours and 55 minutes. TheDART probe, weighing 570 kilograms (1,260 pounds), struck Dimorphos head-on at an astonishing speed of approximately 22,530 kilometers (14,000 miles) per hour.[science+9]
Scientists at the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, who managed the mission for NASA, confirmed the successful impact on September 26, 2022, at 7:14 p.m. EDT (23:14 UTC). Thegoal was to shorten Dimorphos' orbital period by at least 73 seconds. Observations from ground-based telescopes quickly showed the impact far exceeded expectations, reducing the orbital period by a significant 33 minutes.[jhuapl+8]
NASA Administrator Bill Nelson called the mission an "unprecedented success for planetary defense." He stated, "As NASA studies the cosmos and our home planet, we're also working to protect that home, and this international collaboration turned science fiction into science fact, demonstrating one way to protect Earth."[en+5]
The Power of Ejected Debris
The unexpectedly large change in Dimorphos' orbit was not solely due to the spacecraft's direct kinetic force. Scientists determined that the recoil from the massive amount of rocky material ejected from Dimorphos during the collision played a crucial role. This phenomenon, known as "momentum enhancement," meant the debris blasted off the asteroid provided an additional thrust, effectively doubling the punch of the spacecraft alone.[en+3]
Early observations from the Hubble Space Telescope and James Webb Space Telescope, along with Earth-based observatories like ATLAS, detected a long tail of ejecta streaming from Dimorphos after the impact, stretching tens of thousands of kilometers. This visual evidence supported the theory of significant material expulsion. Dimorphos, it turns out, is likely a "rubble pile" asteroid, a loosely packed collection of boulders rather than a solid rock, which contributed to the substantial ejecta cloud.[nationaltoday+6]
Andy Rivkin, a planetary astronomer at the Johns Hopkins University's Applied Physics Laboratory and co-lead for the DART investigation team, highlighted the importance of these findings. "Now that we have the result of the experiment, we can work backwards to see what range of possible starting points give us the sort of period change we saw," Rivkin said.[en+4]
Shifting an Asteroid's Solar Orbit
Beyond altering Dimorphos' orbit around Didymos, new research revealed another groundbreaking outcome: the DART impact also slightly shifted the orbit of the entire Didymos-Dimorphos binary system around the Sun. This marks the first time a human-made object has measurably changed the path of a celestial body around the Sun.[jpl+4]
The binary system's 770-day orbital period around the Sun changed by a fraction of a second, specifically 0.15 seconds. Rahil Makadia, a lead author of the study from the University of Illinois Urbana-Champaign, explained that the change in the binary system's orbital speed was about 11.7 micrometers per second, or 1.7 inches per hour.[jpl+9]
Thomas Statler, lead scientist for solar system small bodies at NASA Headquarters, emphasized the long-term implications of even such a small alteration. "This is a tiny change to the orbit, but given enough time, even a tiny change can grow to a significant deflection," Statler said. He added that this precise measurement further validates kinetic impact as a technique for defending Earth against asteroid hazards.[nationaltoday+5]
Future of Planetary Defense
The DART mission, costing approximately $324.5 million, was a crucial test for humanity's ability to protect Earth from potential asteroid impacts. While neither Dimorphos nor Didymos posed a threat to Earth, the mission demonstrated a viable method to deflect a hazardous asteroid if one were ever discovered on a collision course with our planet.[planetary+2]
Looking ahead, the European Space Agency (ESA) plans a follow-up mission called Hera. Hera is scheduled to arrive at the Didymos system in December 2026 to conduct a detailed "crime scene investigation" of the impact site. Hera will map Dimorphos's surface, study the crater left by DART, and precisely measure the asteroid's mass, providing invaluable data to refine planetary defense models.[en+7]
NASA is also developing the Near-Earth Object (NEO) Surveyor mission, a specialized space telescope designed to detect hard-to-see asteroids that might pose a threat. These ongoing efforts highlight a global commitment to developing robust strategies for planetary defense, moving from theoretical concepts to demonstrated capabilities. As Lori Glaze, director of NASA's planetary division, stated, "We're all here this afternoon because for the first time ever, humanity has changed the orbit of a planetary body." TheDART mission has provided a powerful new tool in humanity's arsenal to safeguard our home planet.[en+6]
