LAUREL, United States —
NASA’s DART mission to test deflecting an asteroid using “kinetic impact” with
a spaceship is just one way to defend planet Earth from an approaching object —
and for now, the only method possible with current technology.
اضافة اعلان
The operation is like playing billiards in space,
using Newton’s laws of motion to guide us.
If an asteroid threat to Earth were real, a mission
might need to be launched a year or two in advance to take on a small asteroid,
or decades ahead of projected impact for larger objects hundreds of kilometers
in diameter that could prove catastrophic to the planet.
Or, a larger object might require hits with multiple
spacecraft.
“This demonstration will start to add tools to our
toolbox of methods that could be used in the future,” said Lindley Johnson,
NASA’s planetary defense office, in a recent briefing.
Other proposed ideas have included a
futuristic-sounding “gravity tractor,” or a mission to blow up the
hypothetical object with a nuclear weapon — the method preferred by Hollywood.
Gravity tractor
Should an approaching object
be detected early — years or decades before it would hit Earth — a spaceship
could be sent to fly alongside it for long enough to divert its path via using
the ship’s gravitational pull, creating a so-called gravity tractor.
This method “has the virtue that the method of
moving the asteroid is totally well understood — it’s gravity and we know how
gravity works,” Tom Statler, a DART program scientist at NASA said at a
briefing last November when DART launched.
The mass of the spacecraft however would be a
limiting factor -- and gravity tractors would be less effective for asteroids
more than 500m in diameter, which are the very ones that pose the greatest
threat.
In a 2017 paper, NASA engineers proposed a way to overcome
this snag: by having the spacecraft scoop material from the asteroid to enhance
its own mass, and thus, gravity.
But none of these concepts have been tried, and
would need decades to build, launch and test.
Nuclear detonation
Another option: launching
nuclear explosives to redirect or destroy an asteroid.
“This may be the only strategy that would be
effective for the largest and most dangerous ‘planet-killer’ asteroids (more
than one kilometer in diameter),” a NASA article on the subject says, adding
such a strike might be useful as a “last resort” in case the other methods
fail.
But these weapons are geopolitically controversial
and technically banned from use in outer space.
Lori Glaze, NASA’s planetary science division
director said in a 2021 briefing that the agency believed the best way to
deploy the weapons would be at a distance from an asteroid, in order to impart
force on the object without blowing it into smaller pieces that could then
multiply the threat to Earth.
A 2018 paper published in the “Journal of
Experimental and Theoretical Physics” by Russian scientists looked at the
direct detonation scenario.
E. Yu. Aristova
and colleagues built miniature asteroid models and blasted them with lasers.
Their experiments showed that blowing up a 200-meter asteroid would require a
bomb 200 times as powerful as the one that exploded over Hiroshima in 1945.
They also said it would be most effective to drill
into the asteroid, bury the bomb, then blow it up — just like in the movie
Armageddon.
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