| Subject: Asteroid to pose close call in 2029 |
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Betty
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Date Posted: 10:54:22 04/12/05 Tue
Astronomer David Tholen spotted it last year in the early evening of June 19, using the University of Arizona's Bok telescope. It was a new "near-Earth object," a fugitive asteroid wandering through space to pass close to Earth.
Tholen's team took three pictures that night and three the next night, but clouds blocked further observations. They reported their fixes to the Minor Planet Center in Cambridge, Mass., and moved on.
Six months later, Tholen's object was spotted again in Australia as asteroid "2004 MN4." In the space of five days, startled astronomers refined their calculations as the probability of the 1,200-foot-wide stone missile hitting Earth rose from one chance in 170 to one in 38.
They had never measured anything as potentially dangerous to Earth. Impact would come on Friday the 13th in April 2029.
Later, additional observations showed that the asteroid would miss, but only by 15,000 to 25,000 miles -- about one-tenth the distance to the moon. Asteroid 2004 MN4 was no false alarm. Instead, it has provided the world with the best evidence yet that a catastrophic encounter with a rogue visitor from space is not only possible but probably inevitable.
It also demonstrated the tenacity of the small band of professionals and amateurs who track potential impact asteroids and highlighted the shortcomings of an international system that pays scant attention to their work.
"I used to say the total number of people interested in this was no more than one shift at a McDonald's restaurant," said David Morrison, an astronomer at NASA's Ames Research Center and a student of near-Earth objects for nearly three decades. "Now it's maybe two shifts."
The vast majority of near-Earth objects are asteroids -- huge rocks or chunks of iron that travel around the sun in eccentric orbits that cross Earth's path periodically. The rest are comets -- ancient piles of dust, stones and ice that come in from the edges of the solar system.
"The good news is that comets represent 1 percent of the danger," said Donald K. Yeomans, who manages NASA's Near-Earth Object Program at the Jet Propulsion Laboratory. "The bad news is that should we find one, there's not a lot we can do about it. . . . We detect them only nine months from impact."
Asteroids, by contrast, generally offer decades or even centuries of warning -- unless they are too small to detect, in which case there is no warning at all.
Asteroid 2004 MN4 is a "regional" hazard -- big enough to flatten Texas with an impact equivalent to as much as 1,600 megatons of dynamite (the largest manmade nuclear explosion had a yield of 50 megatons ).
Even though it will be a near miss in 2029, that will not be the last word. In fact, 2004 MN4 could come close again in 2034, 2035, 2036, 2037, 2038 or later.
So, what can be done? The first thought, depicted in the 1998 movies "Deep Impact" and "Armageddon," is to nuke the intruder into small pieces so it will burn up in Earth's atmosphere.
Many scientists say instead of obliterating the target, such a bomb could break the asteroid into large radioactive chunks capable of transforming huge stretches of Earth into wasteland.
Or the explosion could deflect but not destroy the asteroid, putting it on a future collision course.
Since astronomers ruled out an Earth impact, scientists have continued to observe 2004 MN4 whenever possible, but most of the time it is obscured.
"It would be awfully nice to have information so we don't get surprised," said former Apollo astronaut Russell L. "Rusty" Schweickart, who advocates flying a small interceptor mission to plant a transponder on 2004 MN4 to constantly radio its location, tagging it like a grizzly bear.
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