NASA’s DART Mission Successfully Alters Asteroid System’s Orbit Around the Sun

In a landmark achievement for planetary defense, NASA’s Double Asteroid Redirection Test (DART) mission has not only altered the orbit of the asteroid moonlet Dimorphos around its larger companion, Didymos, but has also measurably shifted the orbit of the entire binary system around the Sun. This marks the first time humanity has demonstrably changed the path of a celestial body’s trajectory around our star.

The DART Impact and Initial Results

Launched in November 2021, the DART spacecraft intentionally collided with Dimorphos, a 160-meter-wide moonlet orbiting the 780-meter-wide asteroid Didymos, on September 26, 2022. Initial assessments revealed that the impact reduced Dimorphos’ orbital period around Didymos by 33 minutes. However, the full extent of the mission’s success was only recently confirmed through long-term observational data.

Measuring the Shift in Heliocentric Orbit

A team of researchers led by Rahil Makadia at the University of Illinois Urbana-Champaign meticulously analyzed data gathered from various sources, including stellar occultations, ground-based astrometric measurements spanning 29 years, and radar measurements. The analysis revealed that the DART impact altered the Didymos binary system’s heliocentric trajectory – its orbit around the Sun – by a fraction of a second over a 770-day period.

The Role of Ejecta and the Momentum Enhancement Factor

The impact wasn’t solely about the kinetic energy of the spacecraft. When DART struck Dimorphos, it ejected a significant amount of pulverized rock and dust into space. This ejecta acted like a “rocket plume,” enhancing the overall momentum transfer. Scientists refer to this effect as the momentum enhancement factor, denoted by beta. In the case of the DART impact, the beta parameter was found to be around two, indicating that the ejecta significantly amplified the effect of the collision.

Stellar Occultation: A Key Technique

A crucial technique used to measure the orbital shift was stellar occultation. This involves precisely timing the brief dimming of a distant star as an asteroid passes in front of it from Earth’s perspective. By analyzing these “blinks” from different locations around the globe, astronomers can pinpoint an asteroid’s position with remarkable accuracy. Between October 2022 and March 2025, 22 stellar occultations of the Didymos system were captured.

Future Observations with the Hera Mission

Further investigation of the DART impact’s effects is planned with the European Space Agency’s Hera mission, scheduled to arrive at the Didymos system later in 2026. Hera will provide a closer look at Dimorphos, including the impact crater created by DART, and will gather more detailed data on the changes to both asteroids. Hera’s observations will be instrumental in refining our understanding of asteroid deflection techniques.

About Didymos

Didymos, discovered in 1996, is an Amor asteroid – a group of near-Earth asteroids with orbits that bring them close to Earth. It is a rapid rotator with a satellite, Dimorphos, orbiting it with a period of approximately 11.9 hours.