Deflecting an asteroid before it hits Earth can result in multiple shocks

There is probably a large space rock somewhere that has Earth in its reticle. Scientists have actually spotted a candidate – Bennu, who...


There is probably a large space rock somewhere that has Earth in its reticle. Scientists have actually spotted a candidate – Bennu, who has a small chance of hitting our planet in the year 2182. But whether it’s Bennu or another asteroid, the question will be how to avoid a very unwelcome cosmic rendezvous.

For nearly 20 years, a team of researchers has been preparing for such a scenario. Using a specially designed pistol, they repeatedly fired projectiles at meteorites and measured how space rocks recoiled and, in some cases, shattered. These observations shed light on how an asteroid could react to a high-speed impact intended to deflect it from Earth.

At the 84th Annual Meeting of the Meteoritical Society held in Chicago this month, researchers presented the results of all this marksmanship. Their results suggest that our ability to push an asteroid away from our planet might depend on the type of space rock we are dealing with and how many times we have touched it.

In the 1960s, scientists began to seriously think about what to do with an asteroid on a collision course with our planet. The main idea at the time was to launch a projectile that would shatter space rock into pieces small enough to burn in Earth’s atmosphere, said George Flynn, a physicist at the State University of New York, Plattsburgh. But scientists have since realized that achieving such a direct and catastrophic blow is a serious challenge.

“It turns out it’s very difficult,” said Dr. Flynn.

Thinking is different today, and it is not the hollywood version with a nuclear bomb either. On the contrary, the current main idea is to set aside an incoming asteroid. The way to do this, scientists generally agree, is to deliberately create a collision between an asteroid and a much smaller, less massive object. Known as the kinetic impact deflection, such a collision changes the trajectory of the asteroid very slightly, with the intention of its orbit changing enough to pass safely through Earth.

“It may barely miss, but barely missing is enough,” said Dr Flynn.

Kinetic impact deflection is a promising – and currently feasible – technique, said Dan Durda, a planetologist at the Southwest Research Institute in Boulder, Colorado. “It doesn’t require science fiction-type technology.”

In 2003, Dr Flynn, Dr Durda and their colleagues began firing projectiles at meteorites to test the limits of kinetic impact deflection. The goal was to determine how much momentum could be transferred to a meteorite without shattering it into shrapnel that could continue on a similar orbital path through the solar system.

“If you break it into pieces, some of those pieces may still be on a collision course with Earth,” said Dr. Flynn.

Similar laboratory studies in the past have primarily fired projectiles at rocks on land. But meteorites are a much better sample, he said, because they are fragments of asteroids. The team is in the process of accessing it.

“It’s hard to convince museum curators to give you a big piece of meteorite so that you can turn it into dust,” said Dr Flynn.

Over many years, researchers have amassed 32 meteorites, most of them purchased from private dealers. (The larger one, roughly the size of a fist and weighing a pound, cost the team around $ 900.)

About half of the meteorites belonged to a type known as carbonaceous chondrites, which tend to be relatively high in carbon and water. The rest were ordinary chondrites, which generally contain less carbon. It is important to note that both types are representative of the near-Earth asteroids which represent the greatest risk to our planet. (Bennu is a carbonaceous chondrite.)

The team turned to an Apollo-era facility to test the reaction of meteorites to high-speed impacts. NASA’s Ames Vertical Fire Range in California was built in the 1960s to help scientists better understand how lunar craters form. It is capable of launching projectiles at over four miles per second, much faster than a rifle.

“It is one of the few guns on the planet that can fire at objects at the characteristic velocity of impacts,” said Dr Flynn.

Working in the facility’s shooting chamber, roughly the size of a walk-in closet, the researchers suspended each space rock from a piece of nylon cord. They then pumped the chamber into a vacuum – to mimic conditions in interplanetary space – and fired tiny aluminum spheres at the meteorites. The team launched spheres ranging in diameter from a sixteenth to a quarter of an inch at different speeds. Several sensors, including cameras that recorded up to 71,000 frames per second, documented the impacts.

The aim was to determine the point at which a meteorite stops being simply pushed by an impact and begins to fragment.

The researchers found a significant difference in the strength of the two types of meteorites they tested. Carbonaceous chondrites tended to fragment much more easily – they could only stand to receive about a sixth of the amount of movement that regular chondrites could receive before shattering.

These results have implications for deflecting a real asteroid, the team suggests. If a higher carbon asteroid was heading our way, it might need to be given a series of gentler nudges to keep it from shattering.

“You may need to use multiple impacts,” Dr. Flynn said.

Next year, researchers will test the kinetic impact deflection on an actual asteroid in the solar system for the first time with NASA Double Asteroid Redirection Test Mission (DART). The spacecraft’s target asteroid, an approximately 525-foot piece of rock known as Dimorphos, is unlikely to strike Earth, however. The mission is launch planned for november.

Laboratory studies of the kinetic impact deflection have shed light on how an asteroid will react to impact, said Nancy Chabot, responsible for coordinating the DART mission and not having participated in the experimental work.

“It’s really important to do these experiments,” said Dr. Chabot, who is also a planetary scientist in the Applied Physics Laboratory at Johns Hopkins University.

The DART mission is to prepare for what is most likely cosmic fate.

“It’s one of those things that we hope we never have to do,” said Dr. Chabot. “But Earth has been touched by objects throughout its history, and it will continue to be touched by objects in the future.”

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Newsrust - US Top News: Deflecting an asteroid before it hits Earth can result in multiple shocks
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