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Thursday, 15 September 2016 15:12

NASA to Land on Asteroid After One Nearly Clobbers Us Featured

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Astronomers shared a collective
sigh of relief last week
when a 100-foot asteroid hurtling
toward Earth missed by 50,000
miles—just a fifth of the distance
to the moon. As comforting as the
avoided terrestrial calamity was,
what remains disturbing is that no
one knew it was coming.
The near miss came just
days before NASA plans to launch
an $800 million probe that will
land on a much larger asteroid, a
remnant from the beginning of the
solar system that should provide
clues to Earth’s origins.
The mission OSIRIS-REx,
which actually stands for something
(Origins Spectral Interpretation
Resource Identification
Security Regolith Explorer), is
slated to blast off on Sept. 8, from
Cape Canaveral, Fla.
The mission “advances our
more practical goals of understanding
the resources of the near earth
Solar System—as well as the hazards,”
Jeffrey Grossman, a mission
scientist, said at a press conference
last month.
The probe will visit a
“near-Earth object” that traces an
orbit around the Sun similar to the
Earth’s. The asteroid, called
Bennu—named by a nine year-old
from North Carolina—recommended
itself for several reasons.
It’s old—basically leftover
pizza dough from the beginning of
the solar system. As a result, it
might contain some of the chemical
secrets about how the Earth
was seeded with the potential for
life.
Being a near-Earth object,
however, doesn’t make Bennu a
pal of our home planet. By being in
the neighborhood, it passes Earth
every six years, coming so close
that scientists give it a 1-in-2,700
chance of hitting us over the next
two centuries.
It's tempting to believe that
Kepler's laws of planetary motion
describes heavenly objects, including
asteroids and comets, as taking
immutable, precisely calculable
tours around the sun. But there's
more to it than that.
OSIRIS-REx will be
measuring a phenomenon
known by
the spy-novel sounding
moniker, “the
Yarkovsky effect.” A
big chunk of rock
can pick up speed as
sunlight heats it up
and the blackness of
space cools it off.
This acceleration
can nudge its heading
slightly. The effect
“acts like a
thruster and changes
the trajectory of the
asteroid,” Dante
Lauretta, the mission's
principal investigator and a
professor at the University of Arizona,
said last month. “So if you
want to predict where an object
like Bennu is going to be in the future,
you have to account for this
phenomenon.”
What it means is that
Bennu, which was discovered in
1999, might still surprise astronomers
when its orbit starts to
more closely track Earth's in 160
years. By collecting precise data on
its composition, shape, and surface
features, NASA hopes it will be
able to document the Yarkovsky effect
in greater detail, and consequently
get a better sense of the
risk asteroids pose to Earth—like
"2016 QA2," the recent near-miss.
NASA, directed by Congress, takes
impact-risk seriously, maintaining
a database of possible hazards and
a scientific scale for categorizing
their threats. The National Research
Council in 2010 published a
report about asteroid risks and
what to do about them. That research
suggests that a rock the size
of 2016 QA2 might have had some
serious local impacts:
Many dozens of people
work for years to launch a mission
that has the complexity of OSIRISREx.
Often, it’s a lifelong dream.
As Canadian Space Agency’s Tim
Haltigin said in this NASA video,
“I grew up playing video games
about shooting lasers at asteroids,
and now it’s my job to shoot lasers
at asteroids. It never stops amazing
me.”
The sample-return spacecraft
can carry up to 4.4 pounds of
space rock. The minimum amount
scientists expect is about 2 ounces.
It's a lot of work for what seems
like a little material—and yet a
much better idea than waiting to
see if the whole 1,600-foot-wide
asteroid slams into earth at the end
of the next century.
Eric Roston
Bloomberg

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