A newly discovered asteroid will miss Earth by about 3 million miles next week but eventually a chunk of space debris will smash into the planet with potentially catastrophic results, scientists warn.
Eugene Shoemaker of the U.S. Geological Survey at Flagstaff, Ariz., said the danger also exists from a small space object hitting the Earth, being mistaken for a nuclear strike and possibly triggering retaliation.
Scientists at a meeting of the American Geophysical Union said there is only one chance in 1,000 that an asteroid a few miles thick–big enough to cause widespread devastation–will hit the Earth in the next century.
They said the most significant hazard may be posed by much smaller chunks of space debris, perhaps only 30 to 60 feet thick, that enter Earth`s atmosphere once every few decades.
Such small objects would explode high in the atmosphere like the airburst of a 1 megaton nuclear weapon, possibly triggering a nuclear strike by a nervous nation thinking it was being attacked, Shoemaker said.
”The real question is if a large number of people see such an event and think they`ve been nuked, what will be the national response?” he said.
It was Shoemaker who reported the discovery May 4 of the asteroid approaching Earth. He estimated the object, which is called 1986JK, is about a half-mile thick. Its orbital path, he said, will carry it about 3 million miles from Earth May 29 or 30.
Shoemaker said objects of that size are believed to come that close to Earth about once a year although they are rarely detected.
”By good fortune, the Earth has not suffered catastrophic loss from an impact by a comet or an asteroid during historic time,” said geologist Joseph V. Smith of the University of Chicago.
But he said ”we continue to fly blind” because of inadequate telescopic searches for chunks of rock or metal that may be following orbital paths that cross Earth`s orbit.
”There could be a severe disaster in the future based on what we know from past events,” Smith said. ”If we don`t do something soon, then I think we are going to be derelict in our moral duty.”
He called for expansion of sky-scanning to look for threatening asteroids and comets. And he suggested an international group be formed to design spacecraft to deflect or destroy a body on a collision course with Earth.
Shoemaker, who has been surveying the sky since 1973, said 57 asteroids are now known to have crossed Earth`s orbit. He and his wife Carolyn discovered many of them.
Based on crater studies on the moon, Shoemaker estimated that an asteroid packing the collision energy of 1 megaton–equal to the detonation of 1 million tons of TNT–could enter Earth`s atmosphere once every 40 to 50 years. He said larger bodies that could hit with the energy of a 10 megaton explosion–equal to a large H-bomb–could hit every 250 to 300 years.
He said objects packing the energy of up to a 10-megaton detonation generally would explode in the atmosphere, sending a tremendous shock wave toward the planet`s surface.
Scientists believe such an event occurred over an uninhabited region near the Tunguska River in Siberia in 1908. Shoemaker estimated the force of that detonation at 12 megatons, knocking down trees 25 miles away and igniting dry timber 9 miles away.
Alan Harris, of the Jet Propulsion Laboratory at Pasadena, Calif., said the possibility that such an atmospheric fireball could be mistaken for a nuclear explosion should be addressed internationally.
He recommended the superpowers establish a system able to issue a warning of at least a few hours of such an impending explosion.
He said that although the United States and the Soviet Union have satellites and other instruments to immediately tell the difference between a natural explosion and a nuclear detonation, there might even be the hazard of a mistake response in the United States.
