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.
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