Deflecting an asteroid like Bennu, which has a small chance of hitting Earth in about a century and a half, could require multiple small impacts from some sort of massive man-made deflection device, experts say.
Scientists in California have fired projectiles at meteorites to simulate the best methods for changing an asteroid’s course so it would not hit Earth.
Based on the results so far, a carbon-rich asteroid like Bennu might need several small bumps to charge its course.
Bennu, which is about a third mile across, has a slightly greater chance of hitting Earth than previously thought, NASA revealed.
The space agency increased the risk that Bennu could hit Earth sometime in the next 300 years to one in 1,750.
According to the NASA study, Bennu also has a one in 2,700 chance of hitting Earth on the afternoon of September 24, 2182.
Scientists have given serious thought to preventing an asteroid from ever hitting Earth since the 1960s, but previous approaches generally involved theories of how to blast the cosmic object into thousands of pieces.
The problem with this is that those pieces could potentially smash into Earth and pose a problem almost as dangerous and threatening to humanity as the original asteroid.
A more recent approach, dubbed Kinetic Impact Deflection (KID), is to launch something into space that more gently knocks the asteroid off its course away from Earth while leaving it intact.
The latest KID effort was presented at the 84th Annual Meeting of the Meteoritical Society in Chicago, chaired by Dr. George Flynn, a physicist at the State University of New York, Plattsburgh.
“You may need to use multiple punches,” said Dr. Flynn speaking to the New York Times. ‘It [Bennu] may scarcely miss, but scarcely missing is enough.’
Researchers have been working on NASA’s Ames Vertical Gun Range for the recent KID experiments, built in the 1960s during the Apollo era and based at Moffett Federal Airfield in California’s Silicon Valley.
They fired small, spherical aluminum projectiles at meteorites suspended from nylon cords.
The team used 32 meteorites – fragments of asteroids that fell to Earth from space – most of which were purchased from private dealers.
The tests have allowed them to find out at what point the momentum of a man-made object fired at an asteroid turns it into thousands of fragments, rather than throwing it off course as desired.
“If you break it into pieces, some of those pieces might still be on a collision course with Earth,” said Dr. Flynn.
Carbonaceous chondrite (C-type) asteroids like Bennu are the most common in the solar system.
Darker than other asteroids due to the presence of carbon, they are among the oldest objects in the solar system – dating back to their birth.
According to experiments at AVGR, the type of asteroid targeted (and how much carbon it contains) can determine how much momentum is directed at it by a man-made KID device.
In the experiments, the researchers found that Type C meteorites could only withstand about one-sixth the momentum that the other chondrites could withstand before fragmenting.
‘[C-type] Asteroids are much more difficult to deflect without interference than ordinary chondrite asteroids,” the experts concluded.
“These results suggest that multiple consecutive impacts may be required to deflect rather than destroy asteroids, particularly carbonaceous asteroids.”
Therefore, some 160 years in the future — when Bennu is most likely to collide with Earth, according to NASA — a KID device would need to give a KID device a series of gentle nudges to prevent it from breaking apart and sending dangerous shrapnel fragments flying toward Earth.
NASA’s most recent study of Bennu, published in Icarus magazine, indicated that there is a greater than 99.9 percent chance that Bennu will not impact Earth in the next three centuries.
“Although the probability of it hitting Earth is 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.