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By Amanda Onion, ABC News
New
Estimates Show There Are More Large Asteroids Near Earth
New estimates show there are 1,100 asteroids
that are more than six-tenths of a mile in diameter near
Earth. Chances are slim that one could strike Earth, but
if it did happen it could have disastrous consequences as
depicted in this NASA illustration.
Oct.
24 — Although space may seem like a vacant place,
the inner solar system is crisscrossed by a scattering of
rocky, fast-slinging projectiles. And new estimates suggest
there may be more traffic out there than previously thought.
“We’ve
run a search that’s been bigger than anyone else’s
by a factor of ten and we found there are more out there,”
says Grant Stokes, the principle investigator for the Lincoln
Near-Earth Asteroid Research Program or LINEAR.
Led by Massachusetts Institute of Technology researcher
Scott Stuart, the LINEAR team used data from two New Mexico-based
telescopes to calculate there are more than 1,100 asteroids
bigger than six-tenths of a mile in diameter screaming in
orbits near Earth.
Why worry about a little galactic traffic? Geologic records
suggest there is good reason for concern.
Foreboding
Traces
Most scientists agree it was a gargantuan-sized asteroid
that caused the extinction of the dinosaurs 65 million years
ago. The meteor that gouged out Arizona’s three-quarter-mile-wide
Meteor Crater 49,000 years ago most likely destroyed all
life for miles around. And, most recently in 1908, a meteor
crashed down in Siberia and devastated more than 1,000 square
miles of forest and wildlife.
Scientists have determined that an object with a diameter
of 10 km or more could extinguish life on earth. Fortunately
such collisions only occur once every 100 million years
or so.
More worrisome are objects six-tenths of a mile or more
in diameter that impact the planet every 500,000 to 10 million
years. Collisions from objects of this size could affect
the global climate, trigger tsunamis and kill billions of
people. So far LINEAR has identified 400 of these asteroids
near Earth.
Chances are slim that a significantly sized asteroid may
strike Earth again in the next few million years, but astronomers
can’t rule out the possibility. In fact in 1996 an
asteroid about a third of a mile wide zoomed within an unnerving
280,000 miles of Earth.
Astronomers only knew about the approaching asteroid four
days before it passed by and would have had no chance of
averting disaster had it been aiming straight for Earth.
That’s why astronomers like Stuart believe it’s
only prudent to track any comets or asteroids within striking
distance.
Planning
Ahead
If an asteroid is on a known path towards Earth, the hope
is scientists could develop a way to either push the asteroid
off course or break it up before it reaches the planet.
“If we continue our work and upgrade our telescopes
there is a good chance that we will be able to discover
all of the [one-kilometer-wide near-Earth asteroids] within
10-20 years,” says Stuart. “And the odds are pretty
low that we’ll get hit before then.”
Since 1998, the LINEAR program has discovered 70 percent
of all near-Earth asteroids detected so far. The key to
LINEAR’s success is its two New Mexico telescopes,
located on a barren stretch of land within eyeshot of the
Trinity atomic test site. The telescopes were originally
designed for the Air Force to track man-made objects, such
as satellites. Three years ago, with the help of NASA funding,
the Air Force began sharing the equipment with researchers
from MIT’s Lincoln Laboratory.
Every night the telescopes take multiple images of patches
of sky and then pick out objects that move within each frame.
Researchers then look for previously unseen moving objects
and send any new data to the Minor Planet Center in Cambridge,
Massachusetts where the asteroids are tracked.
Earlier this year, NASA’s asteroid tracking program
at the Jet Propulsion Laboratory in Pasadena, California
had estimated there are about 700 near-Earth asteroids more
than 0.6 miles in diameter. Stokes explains LINEAR’s
new, higher estimates stem from their ability to look in
new swaths of sky.
Off
the Beaten Path
“Most planets, including the Earth, orbit around the
sun along a single plane,” he says. “Take that
plane and twist it and you have a different inclination.
That’s where we’re finding more things.”
Not only are surprisingly more asteroids located off this
beaten path around the sun, they’re also more difficult
to detect. That’s because when objects are located
above or below the Earth-sun plane, they’re only partially
illuminated by the sun so they’re dimmer and harder
to see from Earth.
NASA’s goal is to find 90 percent of all large-sized
near-Earth asteroids in the next ten years. Based on the
amount of sky that LINEAR has searched so far, the team
knows they have many more to find.
“If the total number is really 750, we’re going
to make the 10-year deadline without breaking a sweat,”
says Stokes. “But if our number is right, we have our
work cut out for us.”
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