Deflecting an asteroid like Bennu, which has a slim chance of hitting Earth within a century and a half, could require multiple small impacts from some kind of massive human-made deflection device, experts say.
Scientists in California have been firing projectiles at meteorites to simulate the best methods to alter an asteroid’s course so it doesn’t hit Earth.
According to the results so far, an asteroid like Bennu that is rich in carbon might need several small bumps to charge its course.
Bennu, which is about a third of a mile across, has a slightly higher chance of hitting Earth than previously thought, NASA revealed.
The space agency raised the risk of Bennu hitting Earth sometime in the next 300 years to one in 1,750.
Bennu also has a one in 2,700 chance of hitting Earth on the afternoon of September 24, 2182, according to the NASA study.
Scientists have been thinking seriously about how to prevent an asteroid from hitting Earth since the 1960s, but previous approaches have generally involved theories about how to blast the cosmic object into thousands of pieces.
The problem with this is that these pieces could expand towards Earth and present a problem almost as dangerous and threatening to humanity as the original asteroid.
A more recent approach, called kinetic impact deflection (KID), involves firing something into space that deflects the asteroid more gently, away from Earth, while keeping it intact.
KID’s recent efforts were described at the 84th annual meeting of the Meteoritical Society held in Chicago and led by Dr. George Flynn, a physicist at the State University of New York, Plattsburgh.
“You may have to use multiple impacts,” Dr. Flynn told The New York Times. ‘This [Bennu] it can barely be missing, but it’s barely enough.”
Researchers have been working at NASA’s Ames Vertical Gun Range, built in the 1960s during the Apollo era and based at Moffett Federal Airfield in California’s Silicon Valley, for the recent KID experiments .
They fired small spherical aluminum projectiles at meteorites suspended by pieces of nylon rope.
The team used 32 meteorites, which are fragments of asteroids that have fallen to Earth from space, which were mostly bought from private traders.
The tests have allowed them to work out when the momentum of a human-made object fired at an asteroid breaks it into thousands of fragments, rather than deflecting it off course as intended.
“If you break it into pieces, some of those pieces may still be on a collision course with Earth,” Dr Flynn said.
Carbonaceous chondrite (C-type) asteroids, such as Bennu, are the most common in the Solar System.
They are darker than other asteroids due to the presence of carbon and are some of the oldest objects in the solar system, dating back to their birth.
According to findings from experiments at AVGR, the type of asteroid being targeted (and how much carbon it has) can dictate the amount of thrust that would be directed at it from any human-made KID device.
From the experiments, the researchers found that the C-type meteorites could withstand only about one-sixth the thrust that other chondrites could withstand before breaking apart.
‘[C-type] asteroids are much more difficult to deflect without disruption than normal chondrite asteroids,” the experts concluded.
“These results indicate that multiple successive impacts may be necessary to deflect rather than disrupt asteroids, particularly carbonaceous asteroids.”
So, around 160 years in the future, when Bennu is most likely to collide with Earth, according to NASA, a KID device would have to give it a series of gentle nudges to prevent it from breaking up and sending dangerous fragments of shard flying towards Earth. .
NASA’s recent study of Bennu, published in the journal Icarus, noted that there is more than a 99.9 percent chance that Bennu will not crash into Earth within the next three centuries.
“Although the chances of it hitting Earth are very low, Bennu remains one of the two most dangerous known asteroids in our solar system, along with another asteroid called 1950 DA,” NASA said in a statement.