Asteroid impacts are frequently brought up as a potential cause of human extinction. A 10–15 kilometer-wide asteroid brought about the abrupt demise of the dinosaurs, and with it the end of the Mesozoic Era. If a similarly-sized asteroid were to fall from the heavens, it would reduce all the fruits of all human labor, wrought over millennia, to unrecognizable rubble. 

Although such a catastrophe is unlikely to happen at any time in the near future, smaller, more mundane asteroids are still dangerous for the planet. Any asteroid with a diameter above 30–50 meters could cause significant damage. Until recently, humanity could do little to prevent these events. Today, however, NASA keeps watch over detected Near-Earth Objects (NEOs), and calculates the danger they present to Earth. Because this is not enough to actually protect the planet, in November 2021, NASA launched a mission to prove that it is possible to save Earth from an asteroid by redirecting the asteroid’s trajectory. Over a year after that mission, NASA has confirmed success.

NASA had planned the mission for five years as a part of its larger planetary defense strategy. The Planetary Defense Coordination Office is the department that organizes the defense strategy, tracking potentially hazardous NEOs, classifying them by the hazard they pose to Earth, and ultimately advising the government as to how it should stop an asteroid from colliding with the planet. The Double Asteroid Redirection Test, as it was named, became the first mission to practice asteroid redirection in real life.

One of NASA’s plans for asteroid redirection is the “kinetic impactor” technique, which is essentially the method of crashing a spacecraft into the asteroid at high speed. The target was the asteroid Dimorphos, about 160 meters in diameter. Dimorphos orbits a larger asteroid named Didymos; neither of them are dangerous, but they were chosen as targets anyway due to their convenient sizes and shared orbit. 

DART launched in November 2021. After about 10 months of travel, it impacted Dimorphos in September 2022. The force of the impact itself, along with the 1 million kilograms of rock ejected from the surface, contributed to the asteroid’s change in orbit. After the collision, the asteroid’s orbit became 33 minutes slower, proving that kinetic impactors can serve to protect the planet from asteroids. These results were recently published in Nature magazine in a a series of five papers.

Because it takes time to design and construct a spacecraft for a mission, NASA will need to know about a potentially dangerous asteroid at least a few years in advance if it plans to use the technique for redirection. With luck, NASA and other space agencies can work together to track all dangerous asteroids and safely change their trajectory, thereby protecting the Earth from impacts in the near future.

References:

1. Moon, Mariella. “NASA’s DART spacecraft took out over 1,000 tons of rock from its target asteroid.” Engadget, 4 March 2023, https://www.engadget.com/nasas-dart-spacecraft-took-out-over-1000-tons-of-rock-from-its-target-asteroid-150139905.html. Accessed 15 March 2023.
2. NASA. “NASA Confirms DART Mission Impact Changed Asteroid’s Motion in Space.” NASA, 11 October 2022, https://www.nasa.gov/press-release/nasa-confirms-dart-mission-impact-changed-asteroid-s-motion-in-space. Accessed 15 March 2023.
3. Osterloff, Emily. “How an asteroid ended the age of the dinosaurs.” Natural History Museum, https://www.nhm.ac.uk/discover/how-an-asteroid-caused-extinction-of-dinosaurs.html. Accessed 15 March 2023.
4. Shakir, Umar. “NASA mission DART proves we can protect Earth from asteroids.” The Verge, 3 March 2023, https://www.theverge.com/2023/3/3/23622808/nasa-dart-mission-asteroid-kinetic-impactor-success. Accessed 15 March 2023.
5. Specktor, Brandon. “NASA confirms humanity can deflect killer asteroids with rockets — but only if we have years to prepare.” Live Science, 2 March 2023, https://www.livescience.com/nasa-confirms-humanity-can-deflect-killer-asteroids-with-rockets-but-only-if-we-have-years-to-prepare. Accessed 15 March 2023.
6. White, Robyn. “NASA Might Have to Take Out a Killer Asteroid Sooner Than It Realized.” Newsweek, 10 March 2023, https://www.newsweek.com/nasa-killer-asteroid-dart-2023dw-esa-1786944. Accessed 15 March 2023.