Asteroid Hunt Goes Granular

A new telescope system featuring the world?s largest digital camera will significantly increase the ability to find space rocks as it begins operation in Hawaii this month, scientists say.

The telescope system will have a wide view of the sky and features a camera that reduces blur in images so that scientists can examine them for signs of asteroids that have moved from one image to the next. The telescope is part of a years-long survey of the sky for asteroids and comets that could pose a threat to our planet.

Since our planet formed 4.5 billion years ago, it has been hit many times by comets and asteroids. While most asteroids are found in our solar system's asteroid belt (between Mars and Jupiter) and don't pose a threat to us, some have orbits that bring them in close proximity to Earth.

The threat

Each year several asteroids ranging in size from basketballs to small cars crash into Earth's atmosphere, typically burning up on the way in or breaking up and raining down in pieces over uninhabited land or the oceans (Earth is two-thirds ocean). In October, an asteroid about the size of a kitchen table exploded in Earth's atmosphere.

Several larger and potentially destructive space rocks have been spotted in recent years as they came a little too close for comfort. A binary asteroid passed within 1.4 million miles (2 million kilometers), or six times as far as the moon, in July. In January, an asteroid as big as several football fields made an even closer pass, coming within about 334,000 miles (537,500 kilometers) of the Earth (the moon is an average of 239,228 miles (385,000 kilometers) away).

Comets strike less frequently but are just as worrisome in the long run. They originate either from the Kuiper Belt (just beyond the orbit of Neptune) or the Oort cloud (far beyond the orbit of Pluto). Many of these icy-rock objects pose no threat to Earth, but astronomers are all but certain the planet has been struck by them in the past and that others will eventually cross our path.

Collectively, asteroids and comets that come close to Earth are known as Near Earth Objects (NEOs). NASA has a Congressional mandate to catalog all NEOs that are at least 0.6 mile (1 kilometer) wide. Several asteroid tracking programs have found thousands of NEOs, but there are still more lurking out there, and the smaller they are, the less likely they are to be spotted. A rock just a quarter mile wide, however, would cause extensive regional destruction if it struck.

First of four

To complete the survey for NEOs, a system of four telescopes called Pan-STARRS (for Panoramic Survey Telescope and Rapid Response System) is being developed at the University of Hawaii's Institute for Astronomy. The first prototype telescope, installed on Haleakala Mountain, Maui, will begin operations this month.

Pan-STARRS's cameras cover an area of sky six times the width of the full moon and can detect objects 10 million times fainter than those visible to the naked eye and has the unique ability to find moving objects.

"This is a truly giant instrument," said the leader of the team that developed the camera, astronomer John Tonry of the University of Hawaii. "We get an image that is 38,000 by 38,000 pixels in size, or about 200 times larger than you get in a high-end consumer digital camera."

When all four telescopes are in place, the entire sky visible from Hawaii (about three-quarters of the total sky) will be photographed at least once a week. Scientists will analyze the resulting images for changes that could reveal a previously unknown asteroid.

They will also combine data from several images to calculate the orbits of asteroids, looking for indications that those orbits might bring them on a collision course with Earth.

Reducing blur

One of the key pieces of technology behind the telescope is a charged-coupled device developed by MIT's Lincoln Laboratory.

In the mid-1990s, researchers Barry Burke, Dick Savoye and Tonry developed a charge-coupled device (CCD), an electronic light sensor used in telescope cameras, ?that can shift its pixels to cancel the effects of random image motion. Many consumer digital cameras have systems to reduce blur from camera motion, but they don?t work at the pixel level and are only effective at much slower speeds.

Pan-STARRS has an added challenge from its wide field of view. For wide fields, movement can vary across the image, so a single shift pattern isn't completely effective. To solve this problem, the researchers made an array of CCDs that can track the variations in motion across the full field of view.

The telescope, funded by the U.S. Air Force Research Laboratory, will also be used to catalog stars and look for planets around other stars.

• Video: Asteroid Hunting
• Video: Killer Comets and Ominous Asteroids
• Images: Asteroids