GARDEN GROVE, California It is past time to get serious about planetary defense, experts say. The threat of Earth being on the receiving end of a cosmic calling card in the form of an asteroid or comet is real.

The four-days of discussion were kicked off by Congressman Dana Rohrabacher, Chairman of the House Science Committee's Space and Aeronautics Subcommittee

Rohrabacher noted that it took the attacks of Sept. 11 for the country to focus on global terrorism. "I hope that it wont take that type of catastrophe for us to start paying attention to the threats of near-Earth objects," he said.

The lawmaker said the political reaction to the worries over space rocks has garnered "a very tepid response" to date, noting that money spent so far on the issue has been "a pittance."

President George W. Bushs new visionary blueprint for NASA including a human return to the Moon and sending astronauts to Mars was saluted by Rohrabacher. That plan, he added, can also support planetary defense objectives.

"The Moon could well be a base of operations that we could use as a means to defend this planet in a timely way, and a more effective way, against near Earth objects," Rohrabacher explained.

Taking a "lets get going," roll-up-your sleeves attitude, Rohrabacher said there is need to start now in readying the technologies necessary to deflect an Earth-threatening object. "What we need to do is build from right herethis moment. The people in this room can save the planet."

There is no question that an asteroid has Earths name on it, astronomers agree. But where the rock is and when that impact is going to occur is unknown, said David Morrison of the NASA Astrobiology Institute at the space agencys Ames Research Center at Moffett Field, California.

NASA now supports -- in collaboration with the United States Air Force -- the Spaceguard Survey and its goal of discovering and tracking 90 percent of the Near Earth Asteroids (NEAs) with a diameter greater than about one-half mile (1 kilometer) by 2008. If one of these big bruisers were to strike our planet, it would spark catastrophic global effects that would include severe regional devastation and global climate change.

By charting the whereabouts of these celestial objects, it is anticipated that decades of warning time is likely if one of the large-sized space boulders was found to be on a heading that intersects Earth.

But a uniform message from the experts attending this weeks planetary defense gathering is extending the survey to spot smaller objects, down to some 500 feet (150 meters) in diameter. These asteroids can wreak havoc too, but on a more localized scale.

For instance, if one of these smaller asteroids were to strike along the California coast, millions of people might be killed, Morrison said. A little further to the east, he added, "a nice crater out in the desert" would become a tourist attraction.

In identifying ways to deal with hazardous asteroids, a first order of business is gaining a better understanding of the enemy. That is, are they fluffy stuff, constituting a rubble pile, or are they tough-as-nails slabs of iron? Along with these physical properties, astronomers want to know more about their overall shape, rotation rate, and whether an object might play host to a smaller companion body.

Developing a robust deflection scheme so an asteroid doesnt hit Earth means taking into account these factors and a host of other issues, said Don Yeomans, a leading asteroid and comet scientist at the Jet Propulsion Laboratory (JPL) in Pasadena, California.

Developing a viable mitigation campaign, Yeomans explained, demands three prerequisites: "You need to find them early. You need to find them early. And we need to find them early."

Now being discussed is a way to flex, test, and calibrate present day computer and hardware tools to first detect and then keep a trained eye on a potential Earth impactor.

There are currently three Earth-impactors en route. But dont worry. Its all friendly fire.

NASAs Genesis spacecraft is headed this way in September of this year. So too is the Stardust spacecraft in January 2006, as will be a Japanese asteroid sample mission in June 2007. All three are designed to reenter the Earths atmosphere and touch down on terra firma, each carrying a precious cargo of scooped-up specimens.

"So we do have current impactors coming back," Yeomans said. While still in the preliminary discussion stage, the idea is to use these incoming spacecraft to shake out coordinated observations, sharpen orbit calculation skills, and help fine-tune procedures now in place for detecting and tracking asteroids and comets, he told SPACE.com.

Yeomans said about 40 objects at least 3 feet (1 meter) in size enter the Earths atmosphere every year. Some of these incoming objects have been observed by space-based infrared and visible sensors and other ground-based detection devices operated by the U.S. military and other government agencies, he said.

"They have indeed made many of these observations available to scientific investigators," Yeomans said. "It would be nicer to get these things [the data] a little more quickly than 3-4 months down the road, he added, with near-simultaneous flow of information about such events seen as ideal.

Space and ground sensors proved useful last year in studying a major meteor explosion in Earths atmosphere. The event also brought home the point of how a natural event can take on the guise of a human-made terrorist act.

Dee Pack, Director of The Aerospace Corporations Remote Sensing Department, detailed a large-scale meteorite fall that occurred over Park Forest, Illinois on March 27, 2003.

"This is the largest meteorite fall over a densely populated area in modern history," Pack and a team of fellow specialists reported at the meeting. The initial mass of the object is now estimated to be nearly 8 tons.

The explosion took place at nearly midnight local time. Fragments of the airbursting meteorite cut through several roofs. The explosive disintegration of the object lit up the night sky to daylight levels. Sonic booms were heard over a wide area. Numbers of meteorites resulting from the event were recovered, later classified as bits of a stony space rock.

Making it all the more jittery for those folks in the fall zone, the object exploded during Operation Iraqi Freedom, with many witnesses worried this natural event was some kind of massive explosion or nuclear event.

Pack and his colleagues contend: "These large meteors, or superbolides, are of concern to the Department of Defense due to their ability to mimic nuclear events." This type of extraordinary Earth-crossing object serves to train global observers to better recognize and characterize these naturally occurring huge explosive events.

A clear and present danger for those studying planetary defense is the lack of any chain-of-command to take on the duties of dealing with the prospect of disruptive collisions from asteroids and comets.

This "who do you call?" factor deserves immediate attention, said Michael Belton of Belton Space Exploration Initiatives in Tucson, Arizona.

Belton detailed the findings of a NASA-sponsored 2002 workshop. It brought together over 75 top scientists, engineers and military experts from the United States, Europe, and Japan to review the science behind mitigating hazardous comets and asteroids.

A central finding: There is lack of any assigned responsibility to any national or international governmental organization to prepare for a disruptive collision. There is absence of any authority to act in preparation for some future collision-mitigation attempt, Belton said.

The 2002 workshop did recommend that NASA be assigned the duty to advance work in beefing up the science and ability to respond to an imminent collision with an asteroid or comet nucleus. Furthermore, the now-in progress Spaceguard Survey should be extended to scope out possible impactors down to 655 feet (200 meters) in size.

In addition, Belton said that there is need for the Defense Department to more rapidly communicate surveillance data on natural airbursts. And lastly, theres need for governmental policy makers to formulate a chain of responsibility for action in the event a threat to the Earth becomes known.

"In other wordsthere isnt anybody to call. There is nobody there. And theres nobody with authoritynobody with any resources," Belton said. "And we need to correct that."