WASHINGTON — A blue-ribbon panel of scientists is trying to determine the best way to detect and ward off any wandering space rocks that might be on a collision course with Earth.
"We're looking for the killer asteroid,'' James Heasley, of the University of Hawaii's Institute for Astronomy, last week told the committee that the National Academy of Sciences created at Congress' request.
Congress asked the academy to conduct the study after astronomers were unable to eliminate an extremely slight chance that an asteroid called Apophis will slam into Earth with devastating effect in 2036.
Apophis was discovered in 2004 about 17 million miles from Earth on a course that would overlap our planet's orbit in 2029 and return seven years later. Observers said that the asteroid — a massive boulder left over from the birth of the solar system — is about 1,000 feet wide and weighs at least 50 million tons.
After further observations, astronomers reported that the asteroid would skim by Earth harmlessly in 2029, but it has a one in 44,000 probability of slamming into our planet on Easter Sunday, April 13, 2036.
Small changes in Apophis' path that could make the difference between a hit or a miss are possible, according to Jon Giorgini, a planetary analyst in NASA's Jet Propulsion Laboratory in Pasadena, Calif.
"We have not eliminated the threat in 2036,'' Lindley Johnson, the manager of NASA's asteroid detection program, told the committee.
The academy panel is headed by Irwin Shapiro, a former director of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. It has a two-part assignment from Congress: Detect and deflect asteroids that might hit earth.
First, the Shapiro committee is supposed to propose the best way to detect and analyze 90 percent of the so-called "near Earth objects'' orbiting between Mars and Venus that are wider than 460 feet by 2020.
About 20 percent of these are identified as potentially hazardous objects because they might pass within 5 million miles of Earth (20 times the distance to the Moon).
More than 5,000 near Earth objects, including 789 potentially hazardous objects, have been identified so far. Johnson predicted that future surveys will find at least 66,000 near Earth objects and 18,000 potentially hazardous objects.
A collision with one or more of these many objects littering the solar system is inevitable, Johnson said. "Once every hundred years there might be something to worry about, but it could happen tomorrow.''
For example, astronomers had only 24 hours' notice of a small asteroid that blew up over northern Africa on Oct. 7. A larger, more dangerous object presumably would be spotted years or decades ahead, giving humans time to change its course before it hit.
The Shapiro panel's second task is to review various methods that have been proposed to deflect or destroy an incoming asteroid and recommend the best options. They include a nuclear bomb, conventional explosives or a spacecraft that would push or pull the asteroid off its course.
Offbeat ideas are painting the surface of the asteroid so that the sun's rays would heat it differently and alter its direction, and a ``gravity tractor, ''a satellite that would fly close to the asteroid, gently nudging it aside.
The earlier that a dangerous asteroid is found, and the farther it is from Earth, the easier it will be to change its trajectory, panel members were told. A relatively small force would be enough while the object is millions of miles away.
The year 2029 could be crucial. When Apophis makes its first pass by Earth, its track can be more precisely determined. That will enable astronomers to judge whether Earth will escape with a near miss or will have to take swift action to avoid a blow that could devastate a region as large as Europe or the Eastern United States.
To deflect an asteroid, scientists need to know its shape, weight and composition. A ball of loose rubble would be handled differently from a solid metallic rock.
"Finding them is one thing, but you have to know your enemy,'' said James Green, the director of NASA's Planetary Science Division.
So far, NASA has spent $41 million on asteroid detection and deflection, but the Near Earth Object Program is running out of money.
"It's just barely hanging on,'' Shapiro said.
Two expensive telescopes to focus on dangerous asteroids have been proposed, but Congress and the incoming Obama administration must be persuaded to approve the money.
"Without new telescopes, we'd never get to 90 percent (detection),'' Johnson said.
After a lot of original skepticism, Congress now looks favorably on the asteroid project, according to Richard Obermann, the staff director of the House Subcommittee on Space and Aeronautics.
"There used to be a high giggle factor among members,'' Obermann said. "But it's now a very respectable area of investigation.''
Johnson told the Shapiro committee that the search for killer asteroids must have a high priority.
"The space program could provide humanity few greater legacies than to know the time and place of any cosmic destruction to allow ample time to prepare our response to that inevitable event,'' he said.
ON THE WEB
NASA's Near Earth Object Program
Near Earth Environment animation 2007-08
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