First it punched an asteroid. Now, a
NASA spacecraft’s rampage
may continue, and it could blast a hole in another space rock.
اضافة اعلان
The Osiris-Rex spacecraft is on its way back to Earth, having
thwacked — briefly — the surface of an asteroid called Bennu last year to scoop
up samples. It will arrive home in 2023, ejecting a capsule full of samples
that may help eager scientists decipher the origin of Earth’s water and life.
But the spacecraft will have plenty of fuel left. Its mission
team wondered: Could it go somewhere else?
Yes, it turns out. And not just anywhere, but one of the most
famous near-Earth asteroids: Apophis.
“We were pretty excited when we found out we could go there,”
said Michael Nolan from the University of Arizona, the science team chief on
the mission, who presented findings this month at the fall meeting of the
American Geophysical Union in New Orleans.
Apophis was once thought to be the asteroid that posed the greatest
threat to Earth. After its discovery in 2004, astronomers rated its chance of
hitting our planet in 2029 as high as 1 in 37, the highest in recorded history
for any asteroid. At 1,000 feet across, it would not end life on Earth if it
hit but would decimate an area hundreds of miles across.
“It was very scary,” Nolan said.
Updated analysis later showed that the asteroid, which dances
around Earth’s orbit, would not impact our planet. But it will still make a
close pass in April 2029 at a distance of 20,000 miles, inside the orbits of
some geostationary satellites, and close enough that it will be visible to the
naked eye in Europe, Asia and Africa.
By coincidence, if mission controllers on Earth directed
Osiris-Rex to complete three flybys of the planet after dropping off its
samples, it would be able to reach Apophis. When the asteroid flies through
Earth’s skies, Osiris-Rex would be just an hour behind, ready to sidle up in
June 2029.
“It’s sort of a fluke,” Nolan said.
While Apophis poses no threat to Earth — at least for the next
century or so — studying it could tell scientists a great deal about asteroids
of this size. No other mission is planned to visit Apophis in 2029, although
there are proposals to do so.
Next month the Osiris-Rex team will put forward its proposal to
NASA to extend the mission, with a decision expected by April. If it goes
ahead, the spacecraft will spend 18 months studying Apophis after it arrives.
While orbiting Apophis, Osiris-Rex would swoop down over the
surface to take high-resolution images. This would include looking for evidence
of landslides caused by the gravitational tug of Earth as the asteroid flew
past.
The spacecraft would also attempt to descend to the surface and
use its thrusters to blast a hole in its surface. The goal would be to expose
underground material, helping to work out what the asteroid is made of.
“Apophis is compositionally the kind of asteroid that’s most
likely to become a hazard,” Nolan said. “The material properties will help us
understand what its structure is.”
This in turn could inform a future mission to save Earth from
Apophis or another asteroid. By working out its mass, density and structure,
scientists will know how spongy or hard the asteroid is, telling them how best
to deal with similar objects.
“We really need to understand what we’re dealing with,” said Jim
Bell, an astronomer at Arizona State University who is not involved in the
Osiris-Rex mission. “Is this a solid hunk of rock? Can we change this thing’s
orbit? Could we destroy it, blow it up into tiny bits, if we had to take some
drastic measures?”
NASA’s ongoing Dart mission, which launched last month, is
performing a not-too-dissimilar experiment by slamming into a small asteroid to
see if scientists can change its orbit.
Davide Farnocchia, from NASA’s Center for Near Earth Object
Studies at the Jet Propulsion Laboratory in California, said the close pass of
Apophis was an “amazing opportunity” to observe an asteroid of this size up
close. It would also lead to better understanding of whether Apophis poses a
future threat to Earth.
After Apophis, Osiris-Rex might even have enough fuel to visit
yet another asteroid. Or, it could be placed on the surface of Apophis and act
as a “tracking beacon,” Nolan said.
Budget constraints or other issues, such as concerns that
Osiris-Rex could inadvertently alter the orbit of Apophis and make it a threat
to Earth, could dictate whether the extended mission is approved. But it could
prove an exciting next chapter for the mission.
“It’s once in a millennium that something this big comes to
Earth,” Bell said. “We should take advantage of that.”
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