Prompted by a close brush between Earth and an asteroid in early January, scores of top researchers who often don't see eye-to-eye have made a joint political plea for help in saving the planet.

The fear: a cosmic sucker punch from southern skies that could destroy civilization.

The remedy: a new multi-million dollar telescope in Australia.

While a coordinated asteroid search program is underway in the Northern Hemisphere, none exists south of the equator, creating a blind spot that equals nearly a third of the heavens. So 91 international astronomers and prominent space activists -- including a who's who of asteroid experts -- sent a letter asking the Australian government to rejoin the asteroid search seven years after the country dropped out.

The letter prods Australia to action, suggesting the country build a telescope. It makes no bones about the stakes involved.

"A major global Spaceguard effort could provide decades of warning prior to an impact," the letter states. "This would be sufficient time to refine the space technology needed to nudge a threatening asteroid into a harmless orbit, or to evacuate the predicted impact area. Without Spaceguard there would be too little warning to prevent a disaster."

The signatories include scientists from NASA and several universities and institutions in America, Europe, Russia and Australia. The voices range widely, from renowned asteroid hunter Carolyn Shoemaker, of the Lowell Observatory, to Ann Druyan, wife of the late Carl Sagan.

Several of the scientists who signed the letter have, from time-to-time, argued over how to conduct the asteroid hunt -- both scientifically and politically. One camp favors focusing on the largest asteroids, which could cause global destruction. Another prefers plans that include smaller rocks that might wipe out a city and, due to sheer numbers, present a greater statistical risk of impact.

The scientists also sometimes disagree over how their findings should be presented, or not presented, to the public. Some have called for full disclosure at times. Others have suggested a more guarded release of information only after public risk, or lack of it, has been well established.

One thing they all agree on, however, is that the threat is real.

The odds of an asteroid larger than 1 kilometer (0.6 miles) hitting Earth sometime in the next century are typically put at 1-in-5,000. Such an impact could destroy a country, would likely cause some species to go extinct, and might blot out the Sun long enough to ruin farming and send humans into a Dark Ages existence, analysts say. Past impacts are recorded in a handful of craters that have not fully eroded.

Smaller events occur as often as once every 100 years and can cause local or regional damage. A comet or asteroid exploded just above the surface of Siberia in 1908, leveling thousands of acres of unpopulated forest.

Don Yeomans of NASA's Jet Propulsion Laboratory is among four scientists there who signed the letter. JPL oversees NASA's asteroid search efforts. In a telephone interview, Yeomans agreed it is unusual for so many of his colleagues to band together on a single political statement.

He added, though, that it was not the first time scientists have tried to arm-twist governments into recognizing the dangers of asteroids and taking action. A similar letter, signed by far fewer researchers, was once sent to the Canadian government, he said.

The letter, mailed from Spaceguard UK, points out that the United States bears the brunt of the burden in looking for asteroids. NASA has a congressional mandate to catalogue all asteroids that roam in the vicinity of Earth's orbit and are at least 0.6 miles (1 kilometer) wide.

While no asteroid is known to be on a collision course with Earth, it is these large Near Earth Objects, or NEOs, that generate the most concern among some researchers because, they say, an impact by one could have global consequences. Over time, their orbits are altered by the gravity of the Sun and planets.

Only about half of these large NEOs have been found, according to the most widely accepted estimates. Some 500 or so are thought to await detection.

Meanwhile, about 30 percent of the sky has never been surveyed, Yeomans said. Pointing to an additional need for a southern telescope, he said, is that when asteroids are discovered in northern skies, they often need to be studied later from the south before their exact paths can be determined.

"It's not that we'll miss them forever, it's just that it will take a lot longer," he said. He said a full-fledged search program Down Under "would definitely help" achieve NASA's goal for 2008.

Large asteroids could be found with an existing, 1-meter (3-foot) Australian telescope that was used for the purpose through 1996. This solution would require no initial investment. Less than $1 million would be needed annually to operate the telescope and pay astronomers, researchers say.

But the thrust of the letter is to encourage the Australians to build a new, larger telescope that would also find small asteroids.

Yeomans notes, however, that larger telescopes, while they can spot small asteroids, cover a smaller region of the sky and so are less effective in finding bigger asteroids.

Construction of a new telescope would run about $7 million for a 2-meter telescope and roughly $21 million for a 3-meter telescope, the ultimate Spaceguard goal, according to Benny Peiser, a researcher at Liverpool John Moores University who is one of the initial authors of the letter.

"This is a highly cost effective investment in the prevention of loss of life and severe economic damage from asteroid impacts," the letter states.

NASA or other U.S. institutions might cover some of the costs, researchers said. Other funding might materialize.

"If Australia were to rejoin Spaceguard, there potentially is a good chance that the UK and other European partners might become interested in a joint project," Peiser said.

The original idea for the plea dates back several years, said Michael Paine, a volunteer with Planetary Society in Australia and a Spaceguard proponent who helped draft the letter.

But a natural impetus came on Jan. 7, when an asteroid the size of three football fields (300 meters wide) passed relatively close to Earth, just twice the distance to the Moon. The rock, named 2001 YB5, was first seen in December -- nowhere near enough time to mount a space mission to deflect it.

"Had it been on a collision course, there is little that could have been done to prevent possibly millions of casualties when an area the size of Tasmania would have been devastated," the signatories agree. Tasmania is about the size of Ohio.

A similar asteroid flyby occurred last October, when a rock thought to be between 50 and 100 meters in diameter zoomed by Earth at a similar distance. The object, big enough to destroy a city, was first detected just two days prior.

The more recent flyby of 2001 YB5 got wide coverage in Australia, however, and a spokesperson for Science Minister Peter McGuaran said the Government would look into renewing the funding of a dedicated Australian Spaceguard program. (McGuaran made a similar statement in 1997, according to press reports from the time.)

Three researchers -- Paine, Peiser, and Australian author and physicist Paul Davies -- jumped on the recent comment and drafted the letter beginning Jan. 10, then sought the signatures.