Pandemics, earthquakes, volcanic eruptions, wars, climate change. There are a lot of disasters that can hit us as humanity. But none are potentially as devastating as a giant asteroid colliding with Earth.

65 million years ago, the dinosaurs went extinct when that happened. The chance is nil in the short term, but such a collision will happen again. So we better prepare for it and try to prevent it, according to space organizations.

NASA will launch a vehicle into a twin asteroid tomorrow morning for a unique test. Can we change the orbit of a celestial body by aiming a probe at it at high speed, as a cosmic cue? The DART mission must answer the question of whether that’s a realistic way to save us from an asteroid on a collision course with Earth.

Collision at 22,000 kilometers per hour

DART stands for Double Asteroid Redirection Test. The mission goes to a double asteroid. Around Didymos – diameter 780 meters – circles the moon Dimorphos – diameter 160 meters. NASA’s probe will arrive there at the end of September next year, when the asteroids are 11 million kilometers from Earth. Then the vehicle is supposed to hit Dimorphos at 22,000 kilometers per hour.

A double asteroid was deliberately chosen, says astronomer Lucas Ellerbroek: “It is easier to effect a change in the orbit of the small asteroid around the large asteroid than the orbit of an asteroid around the sun.” A satellite of the Italian space agency ASI and a probe of the European space agency ESA take images and measure the impact.

When changing the job, we should not imagine too much. “It’s like shooting a pea at a basketball,” Ellerbroek said. If the mission succeeds, the orbit will shift a fraction of a percent, NASA says. “But a small change in orbit can make a big difference, if you do it early enough. The sooner you hit an asteroid, the smaller the push needs to be.”

A little push can make a big difference:

Didymos and Dimorphos themselves pose no threat to Earth. In any case, for the next 100 years, we won’t have to worry about space objects larger than 140 meters that might collide with the Earth, NASA says, even though we only know an estimated 40 percent of those objects. They could theoretically destroy a city, or cause “regional devastation” as NASA describes it. Ellerbroek: “It is better to have practiced once before it is really necessary.”

The asteroid that sealed the fate of the dinosaurs was ten kilometers in diameter. Those objects are much rarer, says Ellerbroek: “With every 10-fold increase in size, comes a 1000-fold increase in rarity.” And the bigger an object, the sooner you spot it and the more time you have to come up with a plan to avoid a collision.

A plot like that of science fiction film Armageddon from 1998, in which scientists only notice eighteen days in advance that an asteroid the size of the state of Texas is heading for Earth is therefore mainly fiction and little science.

Nuclear Explosion

The method they choose there for planetary defense – blowing up the asteroid with an atomic bomb – is also not preferred. A “non-nuclear kinetic impactor” is the “most mature approach yet,” NASA wrote in 2007. A nuclear detonation may be 10 to 100 times more effective, but carries significant “operational and developmental risks.” “If things go wrong,” says Ellerbroek, “radioactive debris may end up on Earth.”

It also depends on what exactly the object coming to Earth consists of. Is it a porous asteroid or a hard comet? The DART mission is also looking at the asteroid’s chemical makeup. For example, NASA’s computer models can be improved to calculate which collision is most effective should it really become necessary to give an asteroid an uppercut into the universe. Whether that will be the case in a hundred, a thousand or a million years.


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