For the first time in history, humans have measurably changed the path of an asteroid around the Sun. The confirmation comes from NASA’s Double Asteroid Redirection Test (DART) mission, which intentionally collided with the asteroid Dimorphos in 2022. While the initial impact was known, the long-term effects have now been precisely quantified.
The DART Mission: A Planetary Defense Test
The DART mission wasn’t about destroying an asteroid, but about testing a crucial planetary defense strategy. Dimorphos orbits a larger asteroid, Didymos, and the goal was to nudge Dimorphos slightly off course using a “kinetic impactor” – essentially, crashing a spacecraft into it. The experiment was designed to determine if this method could be used to divert a potentially Earth-bound asteroid safely.
Measurable Orbit Change
The impact shortened Dimorphos’s orbit around Didymos by 32 minutes. More recently, astronomers observed over 6000 data points to assess the broader effects. They found that the asteroid system’s overall orbit around the Sun has slowed by 11.7 micrometres per second, equivalent to 40 millimetres per hour. This shift will reduce the orbit’s radius by approximately 360 meters.
“It doesn’t sound like a lot, but the whole idea behind these kinetic impacts is that if you do one early enough, a small impact makes a large change in the overall position.”
– Rahil Makadia, University of Illinois Urbana-Champaign
What the Results Mean
The orbital slowdown resulted from two factors: the initial impact and the ejecta plume created when debris flew off Dimorphos’s surface. Researchers found these forces were equal, which also helped them calculate the asteroids’ mass and density. Dimorphos appears to be roughly half as dense as Didymos, supporting the theory that it’s a “rubble pile” formed from material ejected off the larger asteroid over time.
Future Planetary Defense
This mission provides critical data for real-world planetary defense scenarios. The success of DART offers a “solid anchoring point” for predicting future kinetic impact missions. The European Space Agency’s Hera spacecraft, scheduled to arrive at Didymos in November, will provide even more precise measurements to refine these techniques and prepare for any future asteroid threats.
In essence, humanity has taken its first concrete step toward defending Earth from potential asteroid impacts. This experiment demonstrates that small, early interventions can have a significant cumulative effect on an asteroid’s trajectory, offering a viable path toward planetary protection.
