Asteroid Hunt Goes Granular

A newtelescope system featuring the world?s largest digital camera willsignificantly increase the ability to find space rocks as it begins operationin Hawaii this month, scientists say.

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

Since ourplanet 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 (betweenMars and Jupiter) and don't pose a threat to us, some have orbits that bringthem in close proximity to Earth.

Thethreat

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

Severallarger and potentially destructive space rocks have been spotted in recentyears as they came a little too close for comfort. A binary asteroid passedwithin 1.4 million miles (2 million kilometers), or six times as far as themoon, in July. In January, an asteroid as big as several football fields madean evencloser 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).

Cometsstrike less frequently but are just as worrisome in the long run. Theyoriginate 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 poseno threat to Earth, but astronomers are all but certain the planet has beenstruck 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 NearEarth Objects (NEOs). NASA has a Congressional mandate to catalog all NEOsthat are at least 0.6 mile (1 kilometer) wide. Several asteroid trackingprograms have found thousands of NEOs, but there are still more lurking outthere, and the smaller they are, the less likely they are to be spotted. A rockjust a quarter mile wide, however, would cause extensive regional destructionif it struck.

First offour

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

Pan-STARRS'scameras cover an area of sky six times the width of the full moon and candetect objects 10 million times fainter than those visible to the naked eye andhas the unique ability to find moving objects.

"Thisis a truly giant instrument," said the leader of the team that developedthe camera, astronomer John Tonry of the University of Hawaii. "We get animage that is 38,000 by 38,000 pixels in size, or about 200 times larger thanyou get in a high-end consumer digital camera."

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

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

Reducingblur

One of thekey pieces of technology behind the telescope is a charged-coupled devicedeveloped by MIT's Lincoln Laboratory.

In themid-1990s, researchers Barry Burke, Dick Savoye and Tonry developed a charge-coupleddevice (CCD), an electronic light sensor used in telescope cameras, ?thatcan shift its pixels to cancel the effects of random image motion. Manyconsumer digital cameras have systems to reduce blur from camera motion, butthey don?t work at the pixel level and are only effective at much slowerspeeds.

Pan-STARRShas an added challenge from its wide field of view. For wide fields, movementcan vary across the image, so a single shift pattern isn't completelyeffective. To solve this problem, the researchers made an array of CCDs thatcan track the variations in motion across the full field of view.

Thetelescope, funded by the U.S. Air Force Research Laboratory, will also be usedto catalog stars and look for planets around other stars.

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