A First for Humanity Confirmed: NASA's DART Mission Slowed the Asteroid's Orbit

Source: Slashdot

Background

NASA announced a new study documenting a historic first: “the first time a human‑made object has measurably altered the path of a celestial body around the Sun” (NASA press release).

The achievement stems from the 2022 DART mission (Science Slashdot coverage), in which NASA deliberately crashed a spacecraft into the asteroid moon Dimorphos (part of the Didymos binary system).

Findings

• The impact slowed the orbital motion of the Didymos–Dimorphos pair by more than 10 µm s⁻¹.
• Within a month, researchers measured that Dimorphos’ 12‑hour orbital period shortened by 32 minutes (ScienceNews article).
• Some ejecta fragments escaped the gravitational influence of the binary system entirely, carrying away momentum and contributing to the change in the pair’s heliocentric orbit (ScienceNews on boulder escape).

How the Change Was Measured

Astronomers used stellar occultations—brief dimming events when the asteroids passed in front of distant stars—to track the system’s motion. By comparing observed occultation timings with predictions, they determined that the heliocentric orbit was about 150 ms slower than before the impact.

Significance

• Neither Didymos nor Dimorphos poses a threat to Earth, and they were not hazardous before DART.
• Demonstrating that a kinetic impact can reliably alter an asteroid’s orbit provides a concrete proof‑of‑concept for planetary‑defense strategies that might one day be needed against a genuine Earth‑crossing object.

Observational Effort

The research team collected 22 post‑impact position measurements over roughly two and a half years. Much of the data relied on amateur astronomers who traveled to remote locations to observe the occultations. One observer, for example, drove two days each way into the Australian outback to obtain the necessary measurements (as reported by ScienceNews).