quinta-feira, 14 de fevereiro de 2008

Eyes to the Skies Getting Bigger

February 4, 2008
Associated Press/AP Online

By SETH BORENSTEIN WASHINGTON - A telescope arms race is taking shape around the world. Astronomers are drawing up plans for the biggest, most powerful instruments ever constructed, capable of peering far deeper into the universe - and further back in time - than ever before.
The building boom, which is expected to play out over the next decade and cost billions of dollars, is being driven by technological advances that afford unprecedented clarity and magnification. Some scientists say it will be much like switching from regular TV to high-definition.
In fact, the super-sized telescopes will yield even finer pictures than the Hubble Space Telescope, which was put in orbit in 1990 and was long considered superior because its view was freed from the distorting effects of Earth's atmosphere. But now, land-based telescopes can correct for such distortion.
Just the names of many of the proposed observatories suggest an arms race: the Giant Magellan Telescope, the Thirty Meter Telescope and the European Extremely Large Telescope, which was downsized from the OverWhelmingly Large Telescope. Add to those three big ground observatories a new super eye in the sky, NASA's James Webb Space Telescope, scheduled for launch in 2013.
With these proposed giant telescopes, astronomers hope to get the first pictures of planets outside our solar system, watch stars and planets being born, and catch a glimpse of what was happening near the birth of the universe.
"We know almost nothing about the universe in its early stages," said Carnegie Observatories director Wendy Freedman, who chairs the board that is building the Giant Magellan Telescope. "The GMT is going to see in action the first stars, the first galaxies, the first supernovae, the first black holes to form."
When scientists look at a faraway celestial object, they are seeing it as it existed millions and millions of years ago, because it takes so long for light from the object to reach Earth.
Current telescopes are able to look back only about 1 billion years in time. But the new telescopes will be so powerful that they should be able to gaze back to a couple of hundred million years after the Big Bang, which scientists believe happened 13.7 billion years ago. That's where all the action is.
"We hope to answer these questions: Are we alone in the universe? What is the nature of dark matter and dark energy in the universe?" said astronomer Henri Boffin, outreach scientist for the European Southern Observatory.
Two new technologies enable this extraordinary quest - one reliant on modern lasers and computing power and the other inspired by ancient Greek and Roman tilework.
The first is adaptive optics. It allows telescopes on the ground to get rid of the distortion caused when looking through Earth's thick atmosphere into space.
Adaptive optics relies on a laser to create an artificial star, or a constellation of fake stars, in the sky. Astronomers then examine the fake stars and use computers to calculate how much atmospheric distortion there is at any given time. Then they adjust the mirrors to compensate like a pair of eyeglasses. This adjustment happens automatically hundreds of times per second.
Adaptive optics worked first for smaller telescopes. But getting it to work for big observatories was a problem. The first successful use in large telescopes was in 2003 at the twin-telescope Keck Observatory in Hawaii, an effort that took nine years.
The second breakthrough involves technology that makes bigger mirrors possible. Instead of casting a giant mirror in one piece, which is difficult and limits size, astronomers now make smaller mirror segments and piece them together.
Keck scientist Jerry Nelson, now working on the Thirty Meter Telescope, pioneered this technique and said he got the idea from looking at how the Greeks and Romans tiled their baths. This technique is going from 36 segments in current telescopes to 492 segments with his new project.
In astronomy, the bigger the mirror, the greater the amount of light that can be grabbed from the universe. For the past decade and a half, the Keck has had the largest Earth-bound telescopes, with mirrors nearly 33 feet in diameter.
However, three giant land observatories, proposed for construction within the decade, are going to dwarf those:
- The Giant Magellan Telescope. A partnership of six U.S. universities, an Australian college, the Smithsonian Astrophysical Observatory and the Carnegie Institution of Washington will place the telescope in Las Campanas, Chile, around 2016. The plan is for an 80-foot mirror. The cost is around $500 million.
- The Thirty Meter Telescope. The California Institute of Technology, the University of California and the Association of Canadian Universities for Research in Astronomy are aiming for a telescope with about a 98-foot mirror by 2018. No site has been chosen. The cost is about $780 million.
- The European Extremely Large Telescope. A partnership of European countries called the European Southern Observatory already has telescopes in Chile and is aiming for a new one with a mirror of 138 feet, scaled back from initial plans of 328 feet. The Europeans are aiming for a 2018 completion, but have not chosen a specific location yet. The cost would be $1.17 billion.
The managers of these projects are fairly confident they will get the money they need to complete their grand visions. However, some astronomers worry that there may not be enough private or government money for all of them, so they find themselves competing for funding, even as they cheer each other on.
If completed, ESO's European Extremely Large Telescope would be the biggest of the new observatories and should be able to see 20 to 100 times more sharply than the current best land-based telescopes. The Hubble, which set the standard for stunning astronomical pictures, will seem less amazing.
"Oh, you ain't seen nothing yet," said 2006 Nobel Prize-winning physicist John Mather, senior project scientist for NASA's James Webb Space Telescope.
The $4.5 billion Webb Telescope, designed to travel 900,000 miles beyond Earth's orbit, is not faced with the atmospheric distortion of ground telescopes. Still, it will use its own version of adaptive optics. Because of temperature fluctuations in the cold of space, the telescope will have to adjust the shape of its mirrors automatically. Webb's mirror, which is 2 1/2 times bigger than Hubble's, has 18 segments.
While places like Arizona and Hawaii have been successful sites for high-quality space images, Chile is the focal point of the next-generation building boom.
Both the Thirty Meter and European telescope are looking at several sites there although the Thirty Meter team is also considering Baja Mexico and Hawaii. What's needed is the right combination of atmospheric conditions, weather, high altitude, prevailing winds and dark skies.
But there is more in the works than just the super-sized scopes. Smaller, more specialized telescopes are in various stages of design and construction.
The $400 million Large Synoptic Survey Telescope to be built in Chile by 2014 would survey the sky, constantly shooting a movie of 20 billion objects in the cosmos and spotting targets for bigger telescopes.
A planned project in Hawaii would be on the lookout for "killer asteroids." And in Chile, dozens of high-precision antennas are being erected for a huge radio astronomy observatory, called ALMA, that would look into the universe in a different way.
It is the biggest observatories in the works, however, that will provide the dramatic change in astronomical pictures. The pictures to come, Nelson said of the Thirty Meter project, will "knock your socks off, faint stuff that Hubble can't see."
On the Net:
Thirty Meter Telescope: http://www.tmt.org  
Giant Magellan Telescope: http://www.gmto.or  
European Extremely Large Telescope:
James Webb Space Telescope: http://www.jwst.nasa.gov
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