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.
 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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