NASA Confirms It Changed an Asteroid's Solar Orbit

A First in Planetary Defense History

NASA has confirmed a remarkable outcome from its Double Asteroid Redirection Test mission: the DART spacecraft's impact on the asteroid Dimorphos in 2022 not only changed the small asteroid's orbit around its companion Didymos, as intended, but also measurably altered the entire binary asteroid system's orbit around the sun. The finding represents the first time humanity has verifiably changed the solar orbit of a celestial body.

The DART mission was designed as a proof of concept for planetary defense — demonstrating that a kinetic impactor could deflect an asteroid that might one day threaten Earth. The primary success metric was changing Dimorphos's orbit around Didymos, which DART accomplished dramatically, shortening its orbital period by approximately 33 minutes against an expected change of roughly 10 minutes.

The Unexpected Solar Orbit Change

While the change in Dimorphos's local orbit was the mission's primary objective, continued tracking of the Didymos-Dimorphos system has revealed that the entire binary system's orbit around the sun was also affected. The change is small in absolute terms but measurable with modern tracking techniques, and it represents a genuinely unprecedented achievement in human spaceflight history.

The heliocentric orbit change was caused by the momentum transferred during impact. When DART struck Dimorphos at approximately 6.1 kilometers per second, it transferred momentum not just to Dimorphos relative to Didymos but to the entire system relative to the sun. The impact also ejected a significant amount of debris, and the recoil from this ejecta amplified the momentum change beyond what the spacecraft's mass alone would have produced.

Measuring the Change

Detecting the solar orbit change required precise tracking observations conducted over an extended period after the impact. Ground-based telescopes and radar systems monitored the position and velocity of the Didymos system with extreme precision, building up enough data to distinguish the impact-induced orbit change from natural gravitational perturbations and measurement uncertainty.

The measurement campaign involved observatories around the world, coordinating observations to build a comprehensive picture of the system's post-impact trajectory. The fact that the change was detectable speaks both to the magnitude of the DART impact and to the remarkable precision of modern astronomical measurement techniques.