How we'd really defend Earth from an asteroid attack

Caution: This post contains spoilers for Season 5 of The Expanse

The fifth season of The Expanse has delivered some of the most intense drama of the entire series—and it doesn’t even involve ancient alien tech powering up. In Season 5’s third and fourth episodes, the rocks that Belter terrorist Marco Inaros sent hurtling toward the inner solar system last season finally reach Earth.

Three of these stealth-coated asteroids strike humanity’s home world, killing millions and causing widespread destruction. But in a small victory on an otherwise dismal day, a fourth weaponized asteroid is spotted and destroyed by United Nations Navy (UNN) planetary defenses, including an orbital railgun network and nuclear missiles.

It’s a Hail Mary approach, but the basic strategy Earth uses to take out this deadly rock is similar to what scientists say we may have to do in the face of an actual cosmic catastrophe.

“The textbook response if you don't have much warning,” said Mallory DeCoster, a mechanical engineering Ph.D. candidate at the Johns Hopkins University Applied Physics Laboratory, “is going to be a balance between your civil defense mechanisms and a nuclear response.”

DeCoster is a member of NASA’s Double Asteroid Redirection Test (DART) mission team, which is spearheading the first-ever outer space test of a planetary defense strategy. The DART mission, which launches later this year, isn’t going to nuke an asteroid. Instead, scientists will be demonstrating a gentler technique we could use if we had years to prepare for an impending collision: nudging the dangerous bolide onto a different orbit by striking it with a so-called kinetic impactor.

To test this idea, NASA will be crashing a school bus-sized spacecraft into Dimorphos, a 500-foot long moonlet that orbits a larger asteroid called Didymos. The impact will alter the moonlet’s momentum enough to change the speed of its orbit around Didymos, a shift that scientists will observe using telescopes on Earth.