NASA is crashing a spacecraft on purpose to test technology that could save the planet from a killer asteroid.
We live in a dangerous universe.
Medieval theologians believed in an orderly cosmos with the Earth at the center, surrounded by stars and planets fixed in crystalline spheres, all arranged with geometric perfection by the mind of God.
But the truth is that our universe is an ancient, chaotic, turbulent place. Even without considering our propensity to screw up our own habitat, humanity is menaced on every side by natural forces on a colossal scale.
Ways we could all die
The Yellowstone supervolcano could erupt, blanketing North America with ashfall, clouding the sky with a haze of sulfur and plunging the planet into a decades-long volcanic winter. A similar supervolcano eruption at Lake Toba in Sumatra about 75,000 years ago may have reduced the human race to as little as a few thousand survivors.
The Sun could belch out a massive solar flare, inducing electric currents that fry delicate electronics and crucial components of the power grid. A similar flare in 1859, dubbed the Carrington Event, was so powerful that telegraph wires erupted in sparks and flame. Aurora borealis lit up the sky as far south as Cuba. In our digitized world, this could permanently break the internet and cause blackouts that last for months or years.
A nearby giant star could go supernova, instantly becoming the brightest object in the sky, stripping away the ozone layer and scouring the Earth with lethal radiation. Just such an event may have caused the Devonian mass extinction 360 million years ago, when between a quarter and a half of all species on Earth died out.
However, the most iconic disaster—bar none—is a meteor or comet slamming into the Earth. We can all imagine the apocalyptic details: tsunamis engulfing the coast, fire raining from the sky, lava erupting from the wounded planet, a shroud of ash and haze turning the world dark and cold.
But while there’s nothing we could do to stop any of the other megacatastrophes, this may be one that we can defend ourselves against. NASA scientists are planning a test of technology that could save humanity from the fate of the dinosaurs.
Planetary defense—it’s not just for the movies
In November 2021, NASA launched a spacecraft named DART. Its destination is the asteroid 65803 Didymos, about half a mile in diameter, orbiting about 6.7 million miles from Earth. Didymos has a smaller companion, an orbiting moonlet named Dimorphos.
The plan is simple. On September 26, 2022, DART is going to crash into Dimorphos at a speed of 14,000 miles per hour.
If all goes to plan, DART’s impact will alter Dimorphos’ orbit, shortening the time it takes to orbit its parent by several minutes. Astronomers on Earth should be able to measure this change. This won’t accomplish anything by itself, but it serves as a proof of concept that we can alter an asteroid’s course by a desired amount.
The theory is that, for many near-Earth asteroids, there’s a “gravitational keyhole”—a danger zone which, if an asteroid passes through, gravitational forces will alter its trajectory so as to cause it to crash into Earth on its next pass. These keyholes can be surprisingly small: as narrow as half a mile wide. Even a small push or pull at the right time would alter the asteroid’s course enough to make it miss.
All kinds of schemes have been proposed to deflect an asteroid on a collision course. We could blow up a nuclear bomb next to the asteroid, creating a jet of hot vaporized matter that would push it like a rocket engine. We could park a spacecraft nearby so that its miniscule gravitational pull tugs the asteroid onto a new trajectory (“gravity tractor”). We could paint the asteroid white or black so that differential solar heating nudges it (the Yarkovsky effect).
However, the simplest and most foolproof method is an ordinary kinetic impact. That’s what DART delivers.
The DART mission is sponsored by NASA’s Planetary Defense Coordination Office (coolest job title ever!). Its mission is to detect and track asteroids that are close enough and large enough to pose a threat, and to devise ways for us to protect ourselves.
You never see the one that gets you
Space rocks have crashed into Earth countless times over our planet’s history. From Meteor Crater in Arizona to the Popigai crater in Siberia, our world bears the scars of the chaotic cosmos we inhabit. It’s not providence, but simple luck that we haven’t been hit by any civilization-killers in recorded history.
But although we’ve been lucky so far, we may not be lucky forever. We’ve had some close calls.
One such is 99942 Apophis, a large near-Earth asteroid discovered in 2004. There was some alarm when preliminary calculations indicated a small chance that it would hit Earth in 2029.
Fortunately, better data later ruled this out. But Apophis is still going to come unnervingly close. On April 13, 2029, it will pass less than 20,000 miles above Earth’s surface—closer than some orbiting satellites. As NASA says:
At its closest approach to Earth, just before 6 p.m. EDT, April 13, 2029, Apophis will be over the Atlantic Ocean. It will move so fast that it will cross the Atlantic in just an hour. By 7 p.m. EDT, the asteroid will have crossed over the United States.
As it passes by Earth, it will get brighter and faster. At one point it will appear to travel more than the width of the full Moon within a minute and it will get as bright as the stars in the Little Dipper.
The Sentry Risk Table, maintained by NASA, is a database of near-Earth objects we know of that pose a threat. However, there are some whose risk we can’t calculate because of limited data. And there must be many more spinning through the dark that we’ve never spotted at all.
A rational species would spare no expense when it came to monitoring the sky. The odds are low, but the potential payoff is beyond measuring. Ideally, if a large asteroid was headed our way, we’d have decades’ worth of warning, to give us the maximum time to come up with strategies to deflect it. But this mission is a valuable first step in building the tools we’ll need to protect our planet. It’s laying the groundwork to ensure humanity’s survival into the far distant future.