PRAGUE, Czech Republic — The University of Hawai'i's Institute for Astronomy will play a key role in a stepped up global effort to scan the skies for "near-Earth objects," or asteroids and comets on a potential collision course with the planet and big enough to pack a deadly punch.

The International Astronomical Union said yesterday it has set up a special task force to broaden and sharpen its focus on impact threats. Experts say there are an estimated 1,100 known objects that are about a half-mile or wider across — large enough to not only take out a sizable European country but threaten the entire world.

"The goal is to discover these killer asteroids before they discover us," said Nick Kaiser of the UH Institute for Astronomy, whose Pan-STARRS program will train four powerful digital cameras on the heavens to watch for would-be intruders.

The Pan-STARRS, or Panoramic Survey Telescope & Rapid Response System, will be central to the effort because it is the first of a new generation of all-sky survey telescopes. It will be far more powerful than any survey telescope now in operation, said Robert Jedicke, associate specialist for the UH Institute for Astronomy.

A "Pan-STARRS survey should be able to find as many objects in our solar system in one month as are currently known, that have been discovered in the last 200 years," Jedicke said.

This summer astronomers dedicated a prototype on Haleakala of one of four Pan-STARRS telescopes, and astronomers hope to have the four full-size telescopes scanning the skies for potential threats from space by 2010. The PS1 prototype will allow scientists to test the new technology being developed for Pan-STARRS.

Each of the 5.9-foot Pan-STARRS telescopes will be fitted with the world's largest digital cameras, each capable of recording images with 1.4 billion pixels, and will be able to scan and photograph the entire sky visible in Hawai'i three times a month. About three-quarters of the total sky is visible from Hawai'i.

KEEPING WATCH

Parts of the sky where potentially hazardous asteroids are most often found will likely be surveyed more often than once a week, while other areas may be surveyed less often.

The images the telescopes gather will be analyzed by computer to seek out objects that change or move, allowing astronomers to identify objects on trajectories that might threaten the planet.

Funding is being provided by the U.S. Air Force, and astronomers hope to build the full-size Pan-STARRS telescopes on Mauna Kea on the Big Island, which many experts believe has the best astronomical viewing conditions in the world. Pan-STARRS could be built on the site of the UH's existing 7.2-foot telescope.

COMBING THE COSMOS

Other sites participating in the global effort include NASA's Spaceguard Survey, which has identified 800 of the larger near-earth objects and has 103 on an impact risk watchlist. The survey program wants to find 90 percent by the end of 2008.

The U.S. Congress has asked NASA for a plan to comb the cosmos for faint objects as small as 153 yards across and log their position, speed and course by 2020.

Astronomers will have their work cut out for them: Experts say there are about 100,000 such objects hidden among the haze of stars, and as many as 1 million half that size.

One known as the Tunguska object slammed into remote central Siberia in 1908, unleashing energy equivalent to a 15-megaton nuclear bomb that wiped out 60 million trees over an 830-square-mile area. Had it hit a populated area, the loss of life would have been staggering.

Giovanni Valsecchi of Italy's National Institute of Astrophysics said the ultimate aim is a permanent warning system like those that now monitor the Pacific for tsunamis and keep tabs on volcanoes and earthquake zones. The idea: Give the world enough lead time to come up with a workable response to a confirmed threat, such as sending up a rocket to deflect an Earth-bound object or a spacecraft to nudge it into a harmless orbit.

"Right now, unfortunately, there are no 'asteroid busters' or hot lines. Who ya gonna call?" said Andrea Milani Comparetti, a professor of mathematics at the University of Pisa.

FRIGHTENING GLIMPSE

The IAU offered some reassurance yesterday about 99942 Apophis, a smallish asteroid that will come within just 18,640 miles of Earth when it whizzes by in 2029. That's closer than many commercial satellites, and 220,000 miles nearer than the moon.

Last year, scientists were concerned Apophis could come even closer in another fly-by in 2036, with a 1-in-5,500 chance of striking Earth with enough energy to wipe out New York City and its suburbs. However, Comparetti said the latest observations suggest it has only a 1-in-30,000 chance of hitting Earth, and that another initially alarming object, 2004 VD17, now has 1-in-24,000 odds.

"It's not particularly worrying," he said.

Although close encounters are unnerving, they give astronomers a unique opportunity to get a better glimpse of asteroids and comets, the leftover building materials of the universe, and gain a better understanding of the origins of the solar system.

But widening the search for threatening objects creates a problem: Discoveries of potential threats could become commonplace, either creating unnecessary panic and confusion or lulling the public into a false sense of complacency.

"We're now going to be finding such objects once a week instead of once a year," said David Morrison, a NASA scientist who will chair the new IAU task force on impact threats.

FIGURING THE ODDS

To determine the odds of a collision, astronomers surround a target object with a swarm of 10,000 "virtual asteroids" and map out their preliminary orbits. If one is found to be on a path toward Earth, it's given a 1-in-10,000 probability of impact, though — as it did in Apophis' case — fresh data can ease those odds considerably.

"Only in Hollywood do asteroids arbitrarily change orbits," Morrison said.

Ultimately, Valsecchi conceded, mankind may not be able to dodge every cosmic bullet. Earth's craters bear silent witness to what can happen.

"It's through collisions that planets are born," he said, "and through collisions that planets die."

The Associated Press and Advertiser staff writer Kevin Dayton contributed to this report.