Asteroid headed our way will miss by this much
David Perlman, Chronicle Science Editor
November 5, 2011
A massive chunk of black rock bigger than four city blocks is speeding toward us from outer space at more than 30,000 miles an hour.
Scientists say the asteroid won't hit us, but it will be barely more than 200,000 miles away when it passes Earth at 11:13 p.m. Tuesday, and in cosmic terms that's really close.
Astronomers at the Chabot Space and Science Center in Oakland will be tracking the fast-moving object with the center's 36-inch telescope, as will scientists at other observatories around the world.
The asteroid is more than 1,300 feet in diameter - about a quarter-mile - and right now it's invisible from Earth. But amateurs with 6-inch telescopes should be able to pick it up when it flies by late Tuesday night, as it moves swiftly eastward in its orbit around the sun.
"You can spot it until well after midnight right near the horse's nose in the constellation Pegasus," said Gerald McKeegan of the East Bay Astronomical Society, a member of the Chabot observing team.
The asteroid was detected six years ago by Robert S. McMillan, director of the University of Arizona's Spacewatch project, whose telescopes atop Kitt Peak near Tucson survey the skies nightly for what NASA calls NEOs, or Near Earth Objects.
The Spacewatch team relayed its information to Harvard University's Minor Planet Center, which maintains detailed records of asteroids and comets discovered by astronomers from all over the world.
Hazardous object
The astronomical name given this one is 2005 YU55 - a term that designates its discovery date and time. At first, the Minor Planet Center termed the asteroid a "potentially hazardous object" before astronomers determined its course.
Jim Scotti, a Spacewatch research scientist, said the asteroid disappeared from view soon after it was detected, but was rediscovered by other astronomers early last year and was "heavily observed" until April 20, when it disappeared again and hasn't been seen since.
"It is coming from the direction of the sun, so we won't be able to observe it until close to the time of its ... approach," Scotti said. "But no worries since it has been so well observed in the past, we know where it is."
Chemistry like meteorite
Donald Yeomans, director of NASA's Near Earth Object program at the Jet Propulsion Laboratory in Pasadena, said the asteroid is a "C type" object, heavily loaded with carbon and hydrated minerals containing water.
Because of the carbon, it is deeply black, much like the common carbonaceous meteorites that often fall to Earth and that contain the organic chemicals essential for life.
David Morrrison, senior space scientist at NASA's Ames Research Center in Mountain View and an asteroid expert, said objects this size fly past Earth every 20 to 30 years.
"But we haven't by any means discovered all the nearby asteroids," Morrison said. "When we do, we'll probably find they're coming every 10 years or so."
Gravity's pull
As asteroid 2005 YU55 flies on, the gentle tug of Earth's gravity will alter its orbit ever so slightly, Morrison said, and when it passes Venus in 2029, that planet's gravity will change its orbit once again.
The space agency's NEAR Shoemaker spacecraft flew past a huge C-type asteroid named Mathilde in 1997, and images revealed that it was heavily cratered. That asteroid, discovered and named by French astronomers in 1885, is more than 30 miles in diameter.
Tuesday's pass-by will give scientists a rare opportunity for a close-up look at this asteroid, Yeomans said. NASA's Deep Space Network, with huge radio telescopes at Goldstone in the Mojave Desert, has new radar capabilities that should provide exceptional images of 2005 YU55, he said.
"I'm hoping to see if there are craters on its surface that could tell us if it was also scarred by impacts from other objects," Yeomans said.
Source: The San Francisco Chronicle
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