Final score: Earth 1, Asteroid 0

We hit the asteroid. We really hit it off. Watching the live feed of the impact, I admit I cringed. But does the success of the Double Asteroid Redirection Test – DART, for short – mean that the planet is safe from major asteroid strikes?

Not by a long shot. (Sorry.)

Yes, a spacecraft that took off 11 months ago to find out if we could attack and potentially deflect an asteroid in outer space, carried out as designed. It hit Dimorphos, a 170-meter-long asteroid that is in a binary orbit with the larger Didymos. But as an engineer at the Jet Propulsion Laboratory said on the live feed immediately after impact, “Now is where the science starts.”

In particular, scientists will need time to measure the changes in Dimorphos’ orbit and to correlate them with the extensive theories about the usefulness of “kinetic impactors” to protect the planet from asteroid strikes.

Planetary defense, as it has been called, has received increasing attention in recent years. Proponents of interception technology tell us that asteroid strikes are the only catastrophe that we have the technology to both predict and avoid. Economists argue that it is a public good. Legal scholars suggest that governments with the capacity to shoot down asteroids may have a duty under international law to target those headed for nations unable to defend themselves.

Maybe that. But first we have to prove that the capacity exists.

Therefore, the success of the DART mission is important. That we hit the target is a reason to celebrate. But will it work when space debris is actually on its way to us? We will never know for sure until we are forced to try.

NASA is leading a biennial Planetary Defense Conference Exercise, which brings together agencies from around the world to prevent a simulated asteroid strike. In the 2019 version, scientists were tasked with deflecting an asteroid headed for Denver. They succeeded by hitting it with six “kinetic impactors” (like DART) – only to discover, to their dismay, that the impact cut off a large section that would hit Manhattan with 1,000 times the energy of the atomic bombing of Hiroshima.

The simulated disaster was hardly the first. In previous exercises we have lost Dhaka and the French Riviera. In 2019, we would also have lost Tokyo, but the participants used simulated nuclear weapons to destroy the simulated threat. (In the 2021 version, politics got in the way of this solution.)

Hollywood loves to shoot extinction-level objects at the earth, and the results can make great popcorn movies. But the far more likely risk involves “smaller” asteroids like the one that exploded over Chelyabinsk, Russia, in 2013 with a force of over 400 kilotons — more than 20 times the yield of the Hiroshima bomb.

The Chelyabinsk asteroid was only about 20 meters in diameter and its impact was not predicted. What is the annual probability that an object of this size will intercept the Earth? Most calculations suggest that the probability is small, but no one knows for sure.

First, it presents enormous difficulties in predicting the long-term paths of bodies smaller than lunar sizes. (We didn’t even have high-resolution images of Dimorphos until minutes before impact.) For another, although only 500 or so small asteroids orbiting near ours have been cataloged, scientists estimate the true number is well into the millions. On the plus side, this is precisely the area where we can expect kinetic influences to do the most good, even at short notice.

Which now it seems we can – but!

The DART mission cost over $300 million and involved sending a spacecraft 34 million miles to hit an asteroid whose motion is well understood. We had virtually all the time in the world to plan the experiment and carry it out.

When the real-life threat arises – and it will – we don’t know how much time we have. While we would likely have years of warning for larger asteroids, the time involved could be weeks or days with the smaller ones. If we are serious about planetary defense, we need interceptors, plural, ready to go.

And finally we will face a large asteroid. Perhaps not as large as the meteor (possibly a comet) estimated at 50 meters that exploded over Tunguska, Russia, in 1908 with a force of 10 megatons; but a 20 meter long asteroid would destroy most of a fair sized city. That is why we must learn to nudge.

NASA’s two-year simulations remind us that no matter how easily a rogue asteroid is blown to pieces over the course of time in the movies, in the real universe the threatening asteroid must often be encountered early or not at all. The earlier the kinetic impact, the easier the object can be deflected. The 2019 simulation showed an asteroid that began with a 1% chance of hitting Earth in eight years. As fictitious years passed, the probability grew. Eventually it reached 100%. If the world’s (simulated) space agencies had waited to act until the threat was certain, they would have acted too late.

Proponents of space exploration like to argue that everyone benefits. At times, they express the techno-optimism that underpins the Apple+ hit “For All Mankind” — a show bold enough to suggest that if humans had been smart enough to keep going to the moon, we’d have had both cell phones and a female president in the 1990s.

But forget the optimism. We can also support space exploration purely for reasons related to the survival of the species: we will need the technical knowledge that the space program generates. For the day will come, in a century or three, when a huge celestial object will rush our way. If the human race hopes to survive when that happens, the time to practice is now.

More from Bloomberg Opinion:

• A battle between the US and China on the moon is possible and avoidable: Adam Minter

• Behind the fantastic image of the Milky Way’s very own black hole: Faye Flam

• Space Junk Is Our New Tragedy of the Commons: Andreas Kluth

This column does not necessarily reflect the opinion of the editors or Bloomberg LP and its owners.

Stephen L. Carter is a columnist for Bloomberg Opinion. He is a professor of law at Yale University and most recently authored “Invisible: The Story of the Black Woman Lawyer Who Took Down America’s Most Powerful Mobster.”

More stories like this one are available at bloomberg.com/opinion

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