Large Binocular Telescope Searching for Planets
Written by Randal Jackson
Planetquest — Fully assembled, the Large Binocular Telescope resembles a face, gazing skyward with a pair of enormous saucer eyes. That visual impression isn’t too far off the mark: Like humans and many animals, it will combine the optical power of two eyes to see better than one.
Its sharper vision will enable astronomers to carry out a broad range of unprecedented astronomical observations, including some of the first direct observations of giant planets around other stars.
A glaring problem
Astronomers already know that our solar system is not alone in the Universe. At least 100 of the stars in the night sky, just like our Sun, are orbited by planetary companions. But for the time being, no one can actually see those planets because of the blinding glare of the stars they orbit.
The Large Binocular Telescope will overcome this obstacle by suppressing the glare from stars at the centers of planetary systems. Once the glare is removed from view, astronomers can begin to observe the orbiting planets, which are much smaller and fainter than the stars.
The key to canceling out the starlight lies in telescope’s binocular (“two-eyed”) vision. In the case of human vision, each eye captures a separate image of the same target. Information about the two images is combined in the brain to form a single image that contains more detail than either eye sees alone.
In the case of the Large Binocular Telescope, the light from a common target is combined in such a way that the light waves “interfere” with each other, or cancel each other out. Using this interference technique, scientists can make the star disappear from view. It sounds almost like magic, but it’s really just basic physics. (For more details about this technique, see Interferometry: A New Window on the Universe.)
A new spin on mirror technology
Even with the obscuring glare of the star removed, seeing something as small, faint and distant as an extrasolar planet requires exceptionally large mirrors. In the case of the Large Binocular Telescope, each primary mirror is 8.4 meters (28 feet) in diameter. That’s an area large enough to turn around a pickup truck.
Large radio telescope dishes have been around for years, but the technology needed to create very large optical telescope mirrors has come of age only recently. The mirrors for the Large Binocular Telescope were melted, molded and spun into shape in a specially designed rotating oven at the University of Arizona Mirror Lab. An innovative honeycomb structure ensures that the structure is rigid, yet lightweight enough to be practical.
In late October, the first of these mega-mirrors was hauled by truck up 29 tortuous miles of hairpin turns to the observatory site at the summit of Mount Graham in Arizona. The next step is for construction workers to attach the mirror to the motorized support structure, which has taken shape over the past year atop a 10-story tower.
When the second mirror is added, the telescope will have a combined resolution equal to that of a single mirror with a diameter of 22.8 meters (75 feet) — a space big enough to park a passenger bus. At the same time, the combined surface area of the mirrors will be sensitive enough to catch the faint light of planets orbiting stars trillions of miles away.
Even with mirrors this big, Earth-bound astronomers can only hope to observe giant planets like Jupiter, and the dusty discs from which they form. NASA’s long-range goal — the observation of smaller, Earth-size planets that could support life — will require going into space.
That’s where NASA’s Terrestrial Planet Finder (TPF) comes in. Scheduled to launch in just over a decade, TPF will use many of the same technologies that scientists today are perfecting on the ground with the Large Binocular Telescope Interferometer.
“The science results we expect from ground-based projects like the LBTI and Keck Interferometer will really help us understand the type of objects TPF will look at,” said Dr. Rolf Danner, a research scientist at NASA’s Jet Propulsion Laboratory. “They will help us design the right kind of mission.”
Lifting the veil
For the time being, just catching the first glimpse of the mysterious worlds that surround our familiar cosmic neighbors represents a new frontier in astronomy.
For the University of Arizona’s Phil Hinz, principal investigator for the Large Binocular Telescope, the project is all about looking at familiar stars in a new light.
“I really like the approach of building a totally new instrument, then going out and looking at a very well-studied object,” Hinz said. “It’s exciting to think that these well-studied stars might have planetary systems waiting for us to discover, once we have the capability.”
Construction of the Large Binocular Telescope is scheduled to be completed in late 2005, with full science operations to begin a year later. The project is a partnership between the University of Arizona and a consortium of U.S. and international partners. The Large Binocular Telescope Interferometer (LBTI) is a NASA-funded project under the management of the Jet Propulsion Laboratory.
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