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Deflecting an asteroid before it hits Earth has its problems

2021-08-30T18:29:09.024Z


After years of shooting meteorites with a special NASA-owned pistol, they reveal the challenges of cosmic aiming.


Katherine Kornei

08/30/2021 2:48 PM

  • Clarín.com

  • The New York Times International Weekly

Updated 08/30/2021 2:48 PM

There's probably a big space rock out there somewhere that has Earth in its sights.

In fact, scientists have detected a candidate:

Bennu,

which has a slim chance of colliding with our planet in the year 2182.

But whether it is Bennu or another asteroid, the question will be how to avoid an

unwanted cosmic encounter.

The OSIRIS-REx spacecraft on the asteroid Bennu.

.

Lab / Goddard Space Flight Center / NASA via AP.

For almost 20 years, a team of researchers has been preparing for such a scenario.

Using a

specially designed

cannon

, they have repeatedly fired projectiles at meteorites and measured how space rocks recoiled and, in some cases, shattered.

These observations shed light on how an asteroid might respond to a high-speed impact intended to deflect it from Earth.

At the 84th annual meeting of the Meteorological Society, held in Chicago this month, researchers presented the results of all that high-powered aiming.

Their results suggest that the fact that we are able to move an asteroid away from our planet could depend on the type of space rock we face and

the times we hit it

.

In the 1960s, scientists began to seriously consider 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 break space rock into pieces small enough to burn up in Earth's atmosphere, said George Flynn, a physicist at the State University of New York in Plattsburgh.

But scientists have realized that achieving such a direct and catastrophic impact is a

serious challenge.

The asteroid Bennu, seen from the OSIRIS-REX spacecraft.

Photo NASA / Goddard / University of Arizona via The New York Times.

"Turns out it's very difficult," Flynn said.

The thinking is different today, and it's not the Hollywood version of a nuclear bomb either.

The main idea is to

push aside

the approaching asteroid.

The way to do this, according to the scientists, is to deliberately cause a collision between an asteroid and a much

smaller and less massive

object

.

This collision, known as

impact kinetic deviation

, slightly alters the asteroid's trajectory, with the intention that its orbit changes enough to pass harmlessly through Earth.

"It may just fail, but just fail is enough," Flynn said.

Impact kinetic deflection is a promising technique - and currently feasible, said Dan Durda, a planetary scientist at the Southwest Research Institute in Boulder, Colorado.

"It doesn't require science fiction-type technologies."

In 2003, Flynn, Durda, and their colleagues began firing projectiles at meteorites to test the limits of kinetic impact deflection.

The goal was to find out how much momentum could be transferred to a meteorite without breaking it into shrapnel that could follow 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," Flynn said.

In the past, similar laboratory studies have mainly fired projectiles at terrestrial rocks.

But meteorites are a much better sample, he said, because they are fragments of asteroids.

The problem is getting access to them.

"It's hard to convince museum curators to give you a large chunk of a meteorite to turn to dust," Flynn said.

Over many years, the researchers collected 32 meteorites, most of them purchased from private traders.

The largest, the size of a fist and weighing 450 grams, cost the team about $ 900.

About half of the meteorites belonged to a type known as

carbonaceous chondrites

, which are typically relatively rich in carbon and water.

The rest were ordinary chondrites, which usually contain less carbon.

Importantly, both types are representative of the near-Earth asteroids that pose the greatest risk to our planet.

Bennu is a carbonaceous chondrite.

The team turned to an Apollo-era facility to see how meteorites responded to high-speed impacts.

The

Ames Vertical Gun Range

at NASA in California, was built in the 1960s to help scientists better understand how the lunar craters are formed.

It is capable of launching projectiles at more than 6 kilometers per second, much faster than a rifle.

"It's one of the few weapons on the planet that can fire things at the characteristic speeds of impacts," Flynn said.

Working in the facility's firing chamber, about the size of a closet, the researchers suspended each space rock from a piece of nylon rope.

They then pumped the chamber into a vacuum - to mimic interplanetary space conditions - and fired tiny aluminum spheres at the meteorites.

The team launched spheres with a diameter ranging from one-sixteenth to one-quarter inch at different speeds.

Various sensors, including cameras that recorded up to

71,000 frames per second

, documented the impacts.

The objective 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 withstand one sixth of the impulse ordinary chondrites could receive before breaking.

These results have implications for deflecting a real asteroid, the team suggests.

If a more carbon-rich asteroid were heading our way, it might be necessary to give it a series of

gentler nudges

to keep it from breaking apart.

"You may have to use multiple hits," Flynn said.

Next year, researchers will test kinetic impact deflection for the first time on a real asteroid in the solar system with NASA's

Double Asteroid Redirection

Test

(DART) mission.

However, the spacecraft's target asteroid, a roughly 1.5-meter chunk of rock known as Dimorphos, is in no danger of colliding with Earth.

The launch of the mission is scheduled for November.

Laboratory investigations into impact kinetic deviation sheds light on how an asteroid will respond to being impacted, said Nancy Chabot, who is the DART mission coordination leader and was not involved in the experimental work.

"It's very important to do these experiments," said Chabot, who is also a planetary scientist at the Johns Hopkins University Applied Physics Laboratory.

The DART mission tries to be prepared for what is likely to be a

cosmic inevitability.

"It's one of those things that we hope we never have to do," Chabot said.

"But the Earth has been hit by objects throughout its history, and it will continue to be hit by objects in the future."

c.2021 The New York Times Company

Look also

NASA returns to Earth with an asteroid in tow

In a distant galaxy, a close-up look at how a black hole "swallows" a star

Source: clarin

All news articles on 2021-08-30

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