"In
the unlikely event the asteroid had struck Earth in a populated area,
it would have caused considerable loss of life," said Grant
Stokes, the principal investigator for the Lincoln Laboratory Near
Earth Asteroid Research Project, whose New Mexico observatory spotted
the object. "The energy release would be of the magnitude of a
large nuclear weapon."
Another scientist, Brian Marsden of the Harvard-Smithsonian Center for
Astrophysics in Cambridge, Massachusetts, said: "It was a close
shave."
Marsden, whose organization gathers information on all such
encounters, called it "the only object of this size known to have
come closer to the Earth than the moon in decades."
The asteroid, provisionally named 2002 MN, was traveling at more than
23,000 mph (38,000 kph) when it was spotted, Stokes said in a
telephone interview. It was not detected until three days after it
came close to the Earth on June 14. When such asteroids are detected,
they are usually spotted when they are approaching or departing Earth.
With a diameter of between 50 and 120 meters (yards), the asteroid was
about the size of a soccer field, which tend to be about 105 meters
(yards) by 75 meters (yards), Stokes said. The size of asteroids is
estimated by measuring their brightness, without knowing their
composition.
Although lightweight compared with some asteroids, 2002 MN was big
enough to have caused local devastation similar to the impact of one
in Siberia in 1908. On that occasion, an asteroid that exploded above
Tunguska flattened 2,000 square kilometers (1,240 miles) of forest.
The asteroid's air blast was believed to have done the damage, since
no crater was found.
In general, damage on the ground depends on what an asteroid is made
of, varying from solid metal to a loosely bound aggregate.
"Looking statistically at the asteroid population, maybe 50 times
a year a 100-meter-class asteroid passes within a lunar distance of
Earth," Stokes said. "But only a handful of such asteroids
that have penetrated the Moon's orbit have been spotted by asteroid
search programs."
Dr. Benny Peiser, an expert on near earth objects, or NEOs, at
Liverpool John Moore's University in England, said: "Whilst the
vast majority of NEOs discovered do not come this close, such near
misses do highlight the importance of detecting these objects. This
reminder comes in a week when the U.K. telescopes on (the Spanish
island of) La Palma are being tested to search for NEOs."
Currently, there is no dedicated program searching for NEOs of 2002
MN's size, and the American space agency NASA ( news - web sites)
concentrates its efforts on bodies bigger than one kilometer (.62 of a
mile) across.
"NASA has a goal of discovering and obtaining good orbits for all
the near earth objects with diameters larger than 1 kilometer,"
said Thomas Morgan, a scientist at NASA headquarters in Washington.
"Asteroids of this size could potentially destroy civilization as
we know it."
Asked about the discovery of the smaller 2000 MN asteroid, Stokes
said: "We're delighted to have found this object. ... We know
objects in this class are not generally detected."
He also said, "It's something the public should know about, but
shouldn't get nervous about."
Asteroids of that size are estimated to hit the Earth every 100 to
several hundred years, causing local damage, but no disaster to
civilization or the planet's ecosystem, Stokes said.
"Civilization has to get used to them on some level," he
said, adding that larger ones that NASA is trying to detect and
monitor could theoretically hit Earth every million years, or at
longer intervals.
WHAT
IS AN ASTEROID
Whilst
any asteroid hitting Earth is unlikely, it is only unlikely by virtue
of time. At some TIME in the future it is almost 99.9% certain that an
asteroid or comet or some other heavenly body WILL definitely hit the
Earth, in a time to come.