Asteroid attack

Scientists reveal 3 steps to defend Earth from catastrophic asteroid impacts

It is time to get serious about our plans to save the world.

Christine Daniloff, MIT

In 1998's Armageddon, humanity’s only chance of survival hung on Bruce Willis blowing up an asteroid in space, seconds before it collided with Earth and ended the human race. Unfortunately, back in the real world and more than two decades on, the real-life plans to deflect any potential asteroid on a collision course with Earth are not much more advanced — and Bruce Willis tends to get lucky.

Now, scientists at the Massachusetts Institute of Technology have developed three strategies that could help save Earth — and our species — from a devastating asteroid impact. And here's the thing: One of them might actually work.

Armageddon may be fiction, but the fact is we have good reason to worry about asteroid impacts. Some 65 million years ago, a massive asteroid hit Earth and wiped out the dinosaurs. It could happen again — and, if it does, it would have catastrophic consequences for life on Earth. Teams of scientists monitor the skies for these giant asteroids, tracking the objects that zip through our Solar System and their chances of collision with Earth.

Current deflection methods rest on a one shot, one-opportunity style strategy that bets life as we know it on the success of a first, and only, try. But in a new study, the MIT researchers advocate scrapping this all-or-nothing approach and outline three steps that could help deflect asteroids bound for Earth.

They are:

  1. A remote-sensing orbiter to characterize the asteroid's shape, mass distribution, surface properties, and materials.
  2. A sensor to measure its trajectory.
  3. An impactor (i.e. a missile of some kind) to nudge the asteroid off course and back out into space.

“Most of the research in understanding and deflecting asteroids that could threaten the Earth, this goes under the heading of planetary defense,” Olivier de Weck, professor at MIT and lead author of the new study, tells Inverse.

“Most everything you will find there is predicated on the idea of a one shot. You get one shot at this and that is it. That is what we wanted to challenge, no you don’t just get one shot at it,” he says.

The new guidelines are detailed in a paper published this week in the journal Acta Astronautica.

3-step plan

Rather than relying on the success of one, all-or-nothing mission, the ideal asteroid deflection mission is instead a three-step process, the researchers say.

“If you have enough time and you want a high probability of success, what you do is you send three missions,” de Weck says.

Mission one: Characterize

The first mission would involve a preliminary remote-sensing orbiter to characterize the asteroid's shape, mass distribution, surface properties, and the material that it’s made of.

This initial step would be similar to NASA’s OSIRIS-REx, which launched in 2016 and is currently orbiting around Bennu, a potentially hazardous asteroid that could one day threaten Earth. OSIRIS-REx is designed to map the asteroid and bring back a sample from its surface to Earth for scientists to study.

OSIRIS REx is orbiting around asteroid Bennu to characterize this threatening rock.

NASA/Goddard/University of Arizona

Once the orbiter characterizes the asteroid, step two begins.

Mission two: Trajectory

The next step involves a small impact mission designed to hit the asteroid just enough to measure its trajectory — this impact would not be powerful enough to actually deflect the asteroid or change its course.

These two first steps are crucial before the final step to fully deflect the asteroid. Together, they will help scientists account for different variables and uncertainties, the researchers say.

“Nobody has really seriously looked at the impact of uncertainty, what if you don’t know the asteroid really well?” de Weck says.

“You could actually make things worse instead of making them better.”

In the worst case scenario, he compares the asteroid to an apple getting shot by a bullet. The bullet would go straight through, and have very little impact on the apple itself.

In the best case scenario, scientists would know enough about the asteroid ahead of time to enable phase three — the impact.

An artist's impression of the 3-step plan to defend Earth from asteroids in action.


Mission three: Impact

Once steps one and two are complete, step three is to launch a counter defense. The ideal impactor is a basic kinetic impactor, the researchers say, which works by shooting a projectile into space to nudge the asteroid in a different direction.

This would essentially be a missile capable of creating a large enough impact on the asteroid that it would not blow through it, but instead would throw it off course and back out into space.

This last and final phase will hopefully rescue the fate of humanity and not lead to our fiery deaths by asteroid (or by accident).

But this strategy still depends on how much time you have before collision.

Warning time

The researchers based the new 3-step plan on two asteroids, Bennu and Apophis.

Apophis is a near-Earth asteroid that stretches 370 meters in diameter. Named after the ancient Egyptian god of chaos, the asteroid caused panic in December 2014, when scientists estimated a 2.7 percent chance that it might hit Earth in 2029.

This animation shows how close Apophis will get to Earth during its 2029 approach.


These fears rested on the idea that Apophis would pass through a gravitational keyhole — an area in Earth’s gravitational field that would essentially tug on the asteroid’s trajectory.

Once an asteroid goes through a keyhole, that means it is almost guaranteed that it will collide with Earth during its next orbit around the Sun. Which, in the case of Apophis, would be the year 2036.

“The optimal strategy depends on how much warning time you have before keyhole passage,” says de Weck.

Thankfully, subsequent observations have put these fears to rest — Apophis is not on a collision course with Earth. But six years ago, the odds of a collision were 1 in 300 — worryingly close, if you ask us.

If there is ample time, the biggest hurdle would be to change the general attitude around space missions, de Weck says.

Planetary defense research is a young field, spanning just the last two decades, he says. As a result, it is not that far advanced. More time means more hard science to base any Earth-saving missions on — and a higher chance of success.

At the same time, there is a cultural problem in how we conceive of space missions — we tend to send out only one spacecraft at a time, wait for the results, and then send a follow-up mission. This one-by-one approach may hold scientists back in the event of an emergency.

“Part of the work here is to change the thinking and basically think about it with a campaign approach, where you are sending multiple satellites to accomplish a goal that a single satellite couldn’t accomplish,” de Weck says.

“As soon as you think of it as a campaign, you have a lot more degrees of freedom, there’s a lot more possibilities on how you can solve a problem.”

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