An asteroid passing close to Earth is more common than most people realize. Every year, dozens of asteroids that are big enough to cause regional devastation pass within five million miles of Earth. On average, one or two space rocks large enough to cataclysmically impact a continent pass by our planet each year.
Earth will almost certainly confront a space rock large enough to obliterate a city, or worse, at some point in the future. If humans are still around when that day comes, it would be prudent to have a plan for saving the planet. That’s why NASA is launching a spacecraft to conduct the first test of one promising strategy for stopping a killer asteroid: Hit it while it’s still far enough way to alter its course.
Double Asteroid Redirection Test (DART) will slam a spacecraft into the smaller of two asteroids orbiting each other. Any change in the smaller object’s orbit will be easy to measure from Earth and will provide a good indicator of whether it has been deflected.
Two decades ago, a binary system involving a near-Earth asteroid was found to have a moon orbiting it, named Didymos. To be precise, the larger asteroid, which is nearly half a mile (805 meters) across, is orbited by a smaller moon that is 525 feet (160 meters) in diameter called Dimorphos, which means “two forms.” By late 2022, Didymos and Dimorphos will be relatively close to Earth and within 6,835,083 miles (11 million kilometers) of our planet — the perfect time for the DART mission to occur.
The DART spacecraft will deliberately crash into Dimorphos to change the asteroid’s motion in space. This collision will be recorded by LICIACube, a companion CubeSat or cube satellite provided by the Italian Space Agency. The CubeSat will travel on DART and then get deployed from it prior to impact so it can record what happens.
A few years after the impact, the European Space Agency’s Hera mission will follow up Didymos and Dimorphos.
This fast impact will only change Dimorphos’ speed as it orbits Didymos by 1%, which doesn’t sound like a lot, but it will change the moon’s orbital period by several minutes! That change, which is unlikely to be a negative one, can be observed and measured from a ground-based telescope on Earth.
It will also be the first time when humans have altered the dynamics of a solar system body in a measurable way, according to the European Space Agency.