In 2022, NASA deliberately crashed a spacecraft into the small asteroid Dimorphos as part of a planetary defense experiment. The goal was to determine if humankind could safeguard Earth from celestial dangers like asteroids. Recent findings confirm the success of this test, demonstrating a change in the orbits of both Dimorphos and its larger companion, Didymos.
Dimorphos and Didymos constitute a binary asteroid system, implying they orbit each other while simultaneously revolving around the sun; thus, any discernible alteration to one will correspondingly impact the other.
Fresh data indicates that following the Double Asteroid Redirection Test (DART), the period it takes for Didymos and Dimorphos to finish a single orbit around the sun—approximately 770 days—was permanently shortened by under a second, as reported in a study released Friday in the journal Science Advances.
“The orbital velocity of this binary system shifted by approximately 11.7 microns per second, or 1.7 inches per hour,” stated Dr. Rahil Makadia, the lead author of the study, a planetary defense scientist on the DART team who recently earned his PhD in aerospace engineering from the University of Illinois Urbana-Champaign. He added, “Over extended periods, even a minor modification in an asteroid’s trajectory can determine whether a dangerous object impacts or bypasses Earth.”
According to the researchers, the DART mission represents the inaugural instance where a human-made creation has successfully modified the solar orbit of a celestial object—a precedent that could be revisited should an asteroid ever pose an impact threat to Earth.
Even though Didymos and Dimorphos never presented any danger to Earth, this binary system offered NASA an ideal setting to assess the efficacy of a spacecraft as a deflection mechanism.
However, to determine the test’s effectiveness, scientists had to quantify the alterations to Dimorphos and Didymos caused by the collision.
Didymos, resembling a spinning top, is thought to be a “rubble pile” asteroid—a mass of dust and rocks tenuously bound by gravity. Dimorphos, similarly a rubble pile, probably originated from fragments shed by Didymos that subsequently aggregated.
Upon DART’s collision with Dimorphos, an enormous plume of material—estimated at 35.3 million pounds (16 million kilograms)—was ejected into space. Although the 560-foot-wide (170-meter-wide) asteroid lost only 0.5% of its mass, the expelled debris volume was 30,000 times that of the spacecraft itself, as indicated by prior studies.
Researchers concluded that the propulsion from the ejected rubble surpassed the impact force of the spacecraft itself. This momentum boost contributed to shortening the orbital period of the asteroid duo around the sun.
Earlier studies demonstrated a 33-minute reduction in Dimorphos’ 12-hour orbit around Didymos.
This latest research emphasizes that the substantial quantity of matter propelled from the asteroid system also accelerated both space rocks in their solar orbit, resulting in a 0.15-second decrease in their overall orbital duration.
To quantify this orbital modification, astronomers utilized ground-based observations of Didymos and data collected when the asteroid transited directly in front of stars. These events, termed stellar occultations, allow scientists to ascertain an asteroid’s precise position, velocity, and form.
However, detecting the fleeting flicker of a star as an asteroid passes before it from Earth’s vantage point presents a significant challenge. The study’s conclusions were derived from 22 stellar occultations observed by amateur astronomers globally between October 2022 and March 2025.
“When integrated with years of prior ground-based data, these stellar occultation observations proved crucial in enabling us to compute the extent to which DART modified Didymos’ orbit,” remarked Steve Chesley, co-lead author of the study and a senior research scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California. He added, “This endeavor is heavily influenced by weather conditions and frequently necessitates expeditions to secluded locations without assured outcomes. Such a finding would have been unattainable without the unwavering commitment of numerous volunteer occultation observers worldwide.”
Patrick Michel, who leads the European Space Agency’s subsequent Hera mission—launched in 2024 and set to observe the DART collision’s aftermath—expressed astonishment that such a minute orbital discrepancy between the two asteroids could be measured at all.
“We recognized the possibility of such a minuscule alteration, which presents no danger to Earth, but the actual measurement presented a distinct challenge that the team managed exceptionally well,” Michel noted via email. He elaborated, “Achieving this demands meticulously coordinated international efforts, as it involves precisely timing the momentary dimming caused by an asteroid traversing in front of a star, as observed by various individuals across the globe. When executed accurately, as demonstrated in this research, remarkably precise measurements can be obtained.”
Further observations and data regarding DART’s influence on the asteroids will be disseminated once Hera reaches orbit around the asteroid system later this year. Michel stated that Hera is expected to capture and release the initial new images of Dimorphos this fall.
Concurrently, NASA’s Near-Earth Object Surveyor mission, currently under development, has the potential to detect obscure, hazardous asteroids that have largely escaped detection by Earth-based observatories.
The ability to pinpoint hazardous asteroids and comprehend how even a slight orbital adjustment can result in substantial deflection is integral to how space agencies plan to safeguard Earth.
“The exceptionally precise measurement achieved by the team reconfirms kinetic impact as a viable method for planetary defense against asteroid threats and demonstrates how a binary asteroid could be deflected by targeting only one of its components,” stated Thomas Statler, NASA’s lead scientist for solar system small bodies, who was not part of this particular study.
Should a hazardous asteroid be detected sufficiently in advance to allow for deflection, a kinetic impactor similar to DART could be dispatched to gently alter the trajectory of the asteroid, or its partner, steering it into a safer orbit that bypasses Earth.
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