The films are vintage Hollywood, but the villains - comets and asteroids - are plucked from the pages of Earth's geologic past.
As moviegoers flock to theaters to see Earth and its inhabitants take it on the chin in "Deep Impact" and await the release of the other anticipated summer blockbuster, "Arma-geddon," a congressional panel has summoned astronomers and NASA officials to testify today on real-life asteroid hazards.
At issue is whether detection efforts are sufficient and whether enough attention is being paid to ideas about diverting comets and asteroids if that ever becomes necessary.
The hearings before the House Subcommittee on Space and Aeronautics come at a time of heightened public awareness that Planet Earth spins through a rough neighborhood.
In March, for example, the International Astronomical Union's Minor Planet Center in Cambridge, Mass., warned that an asteroid discovered last December could pass as close as 40,000 kilometers (24,800 miles) to Earth in October 2028. Within 24 hours, that distance grew to 950,000 km after researchers found earlier images of the object and refined its projected orbit.
Even discounting this high-profile reversal, "we've had a number of 'fair warnings,'" says a congressional staff member who focuses on space issues. From the Arizona desert and Yucatan Peninsula to the forests of Siberia, Earth's surface displays the weathered dents and flattened forests of past collisions. The hazard came into stark focus in 1994, when comet Shoemaker-Levy 9 broke apart and plunged into Jupiter, punching Earth-sized holes in the Jovian atmosphere.
Heading our way
Earth will get a more subtle reminder of these cosmic hazards in November, when the planet enters a cloud of debris that has boiled off comet Temple-Tuttle. The comet orbits the sun once every 33 years and made its closest approach to the sun in February, adding more material to the cloud.
Known as the Leonid meteor shower, the storm of cometary leftovers - most no bigger than grains of dust and sand - threaten to pummel satellites at speeds approaching those of a .22 caliber bullet, pitting solar panels and even causing electrical failures.
"Normally, you'll see 50 meteors an hour during a typical meteor shower, but we expect that rate to go up to as much as 5,000 an hour" during the Leonid's peak, says William Ailor, director of the Aerospace Corp. Center for Orbital and Reentry Debris Studies in El Segundo, Calif.
"This will be a new experience for spacecraft," he adds, noting that satellites are larger and more numerous than during the comet's last pass. "You just can't simulate these [meteoroid] impact speeds on Earth."
This year the National Aeronautics and Space Administration is spending $3 million on efforts to locate comets and asteroids whose orbits cross or approach Earth's orbit. The agency's goal is to catalog 90 percent of the estimated 2,000 to 3,000 near-Earth objects (NEOs) larger than 1 km within 10 years.
So far, astronomers estimate that they've bagged only about 7 percent of the NEOs they're looking for. But the rate of discovery appears to be accelerating, notes Garith Williams, associate director of the IAU's Minor Planet Center in Cambridge, Mass. Since early March, astronomers have discovered 39 NEOs with two more in the confirmation stage. Twelve have been classified as potentially hazardous. "If this rate can be sustained and improved upon, we'll be doing quite well," he says.
Still, astronomers say more needs to be done. Last week, a National Research Council committee headed by Ronald Greeley. an Arizona State University planetary scientist, recommended that more resources be put into the asteroid-search effort.
"Some things don't take a lot of money," he says, citing the need for closer coordination between various programs scanning the skies for new objects.
Each facility might search a different part of the sky, or be quicker to follow up on a discovery by making the additional observations needed to refine calculations of an object's orbit.
Need for funds
In other cases, more money will be needed, he adds. NASA is spending about $1 million less than the level recommended by a panel of NEO astronomers in 1995, who developed the 90 percent target.
Existing facilities must be equipped with state-of-the-art detectors, while more research is required to develop a new generation of detectors. Moreover, agencies playing a role in the hunt - NASA, the National Science Foundation, and the US Air Force - need to allocate more of their telescope time to NEO work, Dr. Greeley says. Indeed, several astronomers say the Air Force has mothballed some of its space-surveillance telescopes, and they propose putting them back into service as dedicated asteroid and comet hunting tools.
For its part, NASA officials say they are acting on suggestions for closer coordination among the efforts the agency funds. Currently, NASA is underwriting efforts and equipment upgrades for four groups - one at the Jet Propulsion Laboratory in Pasadena, Calif., two at the University of Arizona in Tucson, and one at the Lowell Observatory outside Flagstaff, Ariz.
Based on the results of a meeting of NEO researchers in Houston in March, NASA is "evaluating proposals to set up a coordinating office" for search efforts, says Tom Morgan, NASA's discipline scientist for NEO work. "We're also focusing on finding money to bring technology to bear" on the search.
Reaching the 90 percent goal in 10 years "is technically doable," he maintains. "You don't have to build vast new facilities. We can work within the existing network of telescopes."