Methods for Protecting Earth against an Asteroid Strike

Astronomers following asteroid activity in space estimate there is a very small chance an object large enough to destroy a whole city could strike Earth in 2032.

But space agency officials say even if such an asteroid keeps heading on a path toward Earth, the world is now much better-equipped to defend itself against such a threat.

The American space agency NASA recently estimated there was a 3.1 percent chance that asteroid 2024 YR4 would hit Earth on December 22, 2032. That is the highest probability predicted for such a large space rock in modern times.

Richard Moissl is head of the European Space Agency's (ESA) planetary defense office. While recognizing the risk the asteroid could present, he told the French news agency AFP people should not panic over such predictions.

Astronomers have noted that the more data they gather, the odds of a direct asteroid hit are expected to keep rising over time. However, scientists say at a certain point the odds will likely drop down to zero.

Moissl said he thinks it is important to remember that even in the unlikely event the probability keeps rising to 100 percent, the world is "not defenseless."

Here are some methods currently being considered as defensive measures to keep humanity safe in case there is a real threat.

Send a spacecraft to hit it

Only one planetary defense method has been tried against an asteroid. In 2022, NASA's Double Asteroid Redirection Test (DART) sent a spacecraft into the 160-meter-wide Dimorphos asteroid. The effort successfully changed the asteroid’s orbit around a larger space rock.

Bruce Betts is chief scientist for the nonprofit Planetary Society. He told AFP that space agencies could hit the 2024 YR4 asteroid with several spacecrafts, observing how each one changed the path.

The asteroid discovered in December is estimated to be 40-90 meters wide -- about half the size of Dimorphos.

"You have to take care not to overdo it," Moissl warned. He said this is because if a spacecraft only partly destroys an asteroid, it could send smaller pieces of the space rock heading toward Earth.

Non-contact methods

A separate idea would involve sending a large spacecraft to fly alongside a threatening asteroid. The spacecraft would not touch the asteroid, but would use its gravitational force to pull it away from Earth.

Moissl said another non-contact plan would put a spacecraft near the asteroid to eject a continuous flow of atoms to push the asteroid off course.

Scientists have also considered painting one side of the asteroid white. They believe this could increase the light the object reflects to make it slowly change course.

Contact methods

One idea is to use a nuclear weapon against a threatening asteroid. In laboratory tests, researchers found that X-rays from a nuclear blast could move a rock. But this is considered more of a plan for kilometers-wide asteroids like the one that killed off the dinosaurs. And this method also carries the risk that a nuclear explosion could send additional pieces of the asteroid falling toward Earth.

A similar method – but one considered less dangerous – would involve shooting laser beams from a spacecraft to destroy the side of an asteroid in an effort to push it away from Earth.

If all else fails

Moissl said that if all else fails, at least the world will have a good idea where a threatening asteroid would strike. Since astronomers believe most asteroids would at most threaten to destroy one city, efforts could be organized to get people out of an area before a strike.

"Seven-and-a-half years is a long time to prepare," Moissl added. He also noted that even with the rising odds involving 2024 YR4, there is still about a 97 percent chance the asteroid will miss Earth.

I’m Jill Robbins.

Daniel Lawler with Issam Ahmed reported this story for Agence France-Presse. Jill Robbins adapted it for Learning English.

asteroid - n. any of the small rocky celestial bodies found especially between the orbits of Mars and Jupiter

reflect – v. of light or sound. to move in one direction, hit a surface, and then quickly move in a different and usually opposite direction

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