In Netflix’s upcoming world-ending disaster movie Don’t Look Up, astronomers Leonardo DiCaprio and Jennifer Lawrence inform the US government of an impending comet strike, only to have the White House not take it seriously. With “Based on real events that haven’t happened yet” as a tagline, this could be a cautionary tale. Luckily, NASA is already on it, successfully launching its first-ever planetary defense mission to crash into an asteroid and knock it off course this morning.
Yes, that’s right, NASA is sending a probe into space to purposely collide with an asteroid to determine if this is an effective way of changing the course of any hazardous space rocks heading our way.
Just to be clear, there are no known objects with trajectories that take out Earth currently, including the object of this mission, but it’s best to be prepared. As NASA puts it: "Planetary defense is finding asteroids before they find us."
The Double Asteroid Redirection Test (DART) mission, which launched this morning at 1:20 am EST on a SpaceX Falcon 9 rocket from Vandenberg Space Force Base in California, has a target in mind: the asteroid moonlet Dimorphos, which orbits the larger asteroid, Didymos. The twin system, which doesn't actually pose a threat to Earth, is the perfect target to test out NASA's "kinetic impactor" method. The probe will slam into the 160-meter-wide (525 feet) moonlet at around 24,140 kilometers per hour (15,000 miles per hour) transferring its kinetic energy to the smaller asteroid, pushing it closer to its 780-meter-wide (2,560 feet) asteroid companion. If it works, Dimorphus will orbit Didymos at least 73 seconds faster than before.
Unfortunately, it will take 10 months for the spacecraft to get there, and it will only see Dimorphus about an hour before it is set to collide, so we won't be able to see if it's successful until late next year.
This isn't the first time NASA has considered what to do if a "planet-killer"-sized object was to hit Earth. NASA's Planetary Defense Coordination Office already detects and monitors Near-Earth Objects (NEOs) for potential threats. It tracks any NEOs that orbit the Sun and come within 48 million kilometers (30 million miles) of Earth's orbit with a size large enough (30-50 meters/98-164 feet) to cause significant damage on Earth.
In fact, every two years, the space agency teams up with other agencies around the world for a tabletop exercise to save the planet from a hypothetical incoming asteroid. Unfortunately, the exercise has had mixed results. In 2019, the asteroid was successfully diverted from Denver, but then razed New York to the ground. In May of this year, the exercise failed to prevent a large chunk of Europe from being annihilated after an approaching asteroid was "discovered" that would impact in six months. Experts realized we would need at least five years' notice to deflect an asteroid, hence all the tracking.
So, what is the likelihood of a world-ending object actually hitting Earth? Asteroid Bennu is considered one of the two most potentially hazardous known asteroids in the Solar System. In August this year, NASA refined the probability of Bennu hitting Earth between now and the year 2300 to about 1 in 1,750. The most likely date for an impact is September 24, 2182, and the impact probability for that specific day is 1 in 2,700. So pretty low risk, but like NASA said, best to be prepared, just in case.