ROANOKE TIMES
Copyright (c) 1996, Roanoke Times
DATE: Sunday, May 19, 1996 TAG: 9605200076
SECTION: NATIONAL/INTERNATIONAL PAGE: A-3 EDITION: METRO
DATELINE: BOSTON
SOURCE: DAVID L. CHANDLER THE BOSTON GLOBE
ASTRONOMERS REVEAL that the object, traveling at about 36,000 m.p.h., will make its closest approach today.
An asteroid about one-third of a mile across - detected by astronomers only Wednesday - will whizz by Earth at about 12:48 p.m. today in a dramatic near-miss.
The object, the largest ever observed passing so close, could produce devastation greater than anything in recorded history if it made a direct hit. It will miss Earth by only about 279,000 miles, in astronomical terms a very close call.
There is no chance of an actual collision, scientists said Friday. Since the asteroid's discovery, astronomers at several observatories have carefully monitored its position and precisely calculated its four-year orbit around the sun.
It will come closer to Earth than all but five other objects ever detected - but not quite so close as the moon. Another recently discovered asteroid, perhaps three-quarters of a mile across, is expected to pass within 1.9 million miles of Earth on May25.
Timothy Spahr, a graduate student in astronomy at the University of Florida who made the latest discovery, said in an interview Friday from the Mount Lemmon observatory outside Tucson that if an object of this size were to collide with Earth, ``It would be very bad, but it wouldn't wipe out everything.''
If it were on a collision course, the asteroid, called 1996 JA-1, might leave a crater several miles wide if it struck land, devastating an area perhaps hundreds of miles across. If it struck in the ocean, it would produce tsunamis, or tidal waves, that would travel many hundreds of miles and devastate coastlines with waves towering nearly 200 feet high.
The impact, astronomers calculate, might produce a blast equivalent to 3,000 to 4,000 megatons of TNT - almost as much as all of the world's nuclear bombs going off at once - according to calculations by astronomer Duncan Steel of the Anglo-Australian Observatory, which he posted Friday on the Internet.
The asteroid is about one-tenth the diameter of the object believed to have collided with Earth and caused global devastation 65 million years ago, killing off all the dinosaurs and most other living plants and animals by shrouding the Earth with dust for several years.
James Scotti, an astronomer in Tucson who is part of another team scanning the skies for asteroids that might collide with Earth someday, said this object is probably just below the threshold size at which an impact could cause global havoc.
But it is far larger than any of the other ``near-miss'' objects recorded, all of them spotted in the last five years.
As the object makes its closest approach today, traversing the constellation Sextans, just south of Leo, it will be far too faint to be seen with the naked eye or even binoculars, but will be observable by amateur astronomers with moderate-size telescopes.
But because it will be moving across the sky so fast - it will cross a distance about 18 times the width of the full moon in one hour - large telescopes such as the Hubble Space Telescope will probably be unable to move fast enough to track it. Its speed through space is about 10 miles per second, or about 36,000 mph.
LENGTH: Medium: 66 linesby CNB