More than 10,000 asteroids and comets that can pass near Earth have
now been discovered. The 10,000th near-Earth object, asteroid 2013 MZ5,
was first detected on the night of June 18, 2013, by the Pan-
STARRS-1
telescope, located on the 10,000-foot (3,000-meter) summit of the
Haleakala crater on Maui. Managed by the University of Hawaii, the
PanSTARRS survey receives
NASA funding.
Ninety-eight percent of all near-Earth objects discovered were first detected by
NASA-supported surveys.
“Finding 10,000 near-Earth objects is a significant milestone,” said Lindley Johnson, program executive for
NASA’s Near-Earth Object Observations Program at
NASA
Headquarters, Washington. “But there are at least 10 times that many
more to be found before we can be assured we will have found any and all
that could impact and do significant harm to the citizens of Earth.”
During Johnson’s decade-long tenure, 76 percent of the
NEO discoveries have been made.
Near-Earth objects (
NEOs) are asteroids
and comets that can approach the Earth’s orbital distance to within
about 28 million miles (45 million kilometers). They range in size from
as small as a few feet to as large as 25 miles (41 kilometers) for the
largest near-Earth asteroid, 1036 Ganymed.
Asteroid 2013 MZ5 is approximately 1,000 feet (300 meters) across.
Its orbit is well understood and will not approach close enough to Earth
to be considered potentially hazardous.
“The first near-Earth object was discovered in 1898,” said Don Yeomans, long-time manager of
NASA’s
Near-Earth Object Program Office at the Jet Propulsion Laboratory in
Pasadena, Calif. “Over the next hundred years, only about 500 had been
found. But then, with the advent of
NASA’s
NEO
Observations program in 1998, we’ve been racking them up ever since.
And with new, more capable systems coming on line, we are learning even
more about where the
NEOs are currently in our solar system, and where they will be in the future.”
Of the 10,000 discoveries, roughly 10 percent are larger than
six-tenths of a mile (one kilometer) in size – roughly the size that
could produce global consequences should one impact the Earth. However,
the
NASA NEOO program has found that none of these larger
NEOs currently pose an impact threat and probably only a few dozen more of these large
NEOs remain undiscovered.
The vast majority of
NEOs are smaller than
one kilometer, with the number of objects of a particular size
increasing as their sizes decrease. For example, there are expected to
be about 15,000
NEOs that are about
one-and-half football fields in size (460 feet, or 140 meters), and more
than a million that are about one-third a football field in size (100
feet, or 30 meters). A
NEO hitting Earth would
need to be about 100 feet (30 meters) or larger to cause significant
devastation in populated areas. Almost 30 percent of the 460-foot-sized
NEOs have been found, but less than 1 percent of the 100-foot-sized
NEOs have been detected.
When it originated, the
NASA-instituted
Near-Earth Object Observations Program provided support to search
programs run by the Massachusetts Institute of Technology’s Lincoln
Laboratory (
LINEAR); the Jet Propulsion Laboratory (
NEAT); the University of Arizona (Spacewatch, and later Catalina Sky Survey) and the Lowell Observatory (
LONEOS).
All these search teams report their observations to the Minor Planet
Center, the central node where all observations from observatories
worldwide are correlated with objects, and they are given unique
designations and their orbits are calculated.
“When I began surveying for asteroids and comets in 1992, a
near-Earth object discovery was a rare event,” said Tim Spahr, director
of the Minor Planet Center. “These days we average three
NEO
discoveries a day, and each month the Minor Planet Center receives
hundreds of thousands of observations on asteroids, including those in
the main-belt. The work done by the
NASA surveys, and the other international professional and amateur astronomers, to discover and track
NEOs is really remarkable.”
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