Mar 14, 2001

Welcome Interference




NASA scientists have combined starlight from two of the largest telescopes on Earth to form an extraordinary new tool in the search for planets outside the solar system.


Marshall Space Flight Center


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March 15, 2001 -- Proving that two telescopes are better than one, NASA astronomers have combined starlight from a pair of Hawaiian 10-meter (33-foot) telescopes, creating an "optical interferometer" with the resolving power of a huge single telescope 85 meters wide -- nearly the size of a football field.


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This successful test at the W.M. Keck Observatory on Mauna Kea makes the linked telescopes, which together are called the Keck Interferometer, the world's most powerful optical observing system. The project will eventually search for planets around nearby stars and help NASA design future space-based missions that can search for habitable, Earth-like worlds.


Right: At the summit of Mauna Kea, Hawaii, NASA astronomers have linked the two 10-meter (33-foot) telescopes at the W.M. Keck Observatory. [more]

"Successfully combining the light from two of the largest telescopes on Earth is a fabulous technical advance," said Anne Kinney, director of NASA's Astronomical Search for Origins program, which includes the Keck Interferometer project.

Paul Swanson, the Keck Interferometer project manager at NASA's Jet Propulsion Laboratory (JPL) agreed. "This is a major step in the creation of a whole new class of astronomical telescopes. Historically, breakthrough technologies like the Hale 200-inch and the Hubble Space telescopes have made discoveries way beyond the purpose for which they were originally built."

Since 1995, astronomers have discovered almost 50 planets orbiting other stars. With current technology, which relies mainly on radial velocity (or "Doppler Shift") techniques to detect planets in an indirect fashion, they can find very large worlds, 300 times as massive as Earth, that are located close to their parent stars. Such planets -- called "Hot Jupiters" -- are not likely to harbor life as we know it.


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Using a technique called interferometric nulling, scientists hope to directly detect Hot Jupiters with the Keck Interferometer. The powerful pair of telescopes might also reveal planets farther from their parent stars, which means their reflected light would be dimmer and harder to detect.

Left: Nulling is a process that reduces the light recorded from the central star of a planetary system, while leaving the planet's light undimmed. Credit: Terrestrial Planet Finder.

Nulling might also reveal faint dusty disks surrounding nearby stars, a telltale sign of planetary systems. Our own solar system is permeated with space dust. (The elusive Zodiacal Light, which sharp-eyed sky watchers can spot in the night sky, are sunlight reflected from interplanetary dust.) These tiny particles are leftovers from the formation of the planets billions of years ago, along with bits of debris from comets and asteroids. The amount of such dust orbiting other stars is poorly known, but perhaps not for long. The Keck Interferometer can sense clouds of so-called "exozodiacal dust" comparable in size to the dust swarm inside our own solar system.

Exozodiacal dust is a noise source for future space missions like the Terrestrial Planet Finder (TPF), an interferometer that will seek out Earth-like planets by looking directly for their infrared emissions. By probing exozodiacal dust around nearby stars and by testing key technologies, the Keck Interferometer will be an important pathfinder for the TPF.


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Above: This dusty disk, viewed edge on surrounding Beta Pictoris, a star only 50 lightyears distant, may signal the presence of an infant solar system. Credit: Hubble Space Telescope. [more information]

On Monday, March 12, 2001, starlight from HD61294, a faint star in the constellation Lynx, was captured by both Keck telescopes and transported across a sophisticated optical system spanning the 85 meters (275 feet) separating the two telescopes. In an underground tunnel the collected light waves were combined and processed with a beam combiner and camera. In order to properly phase the two telescopes, adaptive optics removed the distortion caused by the Earth's atmosphere.




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"This first light from the Keck Interferometer marks a dramatic step forward and will help us accomplish the ultimate goal of the Origins Program -- to search for signs of life beyond by examining the light from 'Earths' orbiting nearby stars," said Charles Beichman, the Origins chief scientist at JPL.

Testing will continue for the next several months. Limited science operations, including the search for planets, are expected to begin this fall. Scientists around the world will soon be invited to propose studies they would like to conduct using the Keck Interferometer. Their proposals will undergo a formal review and selection process.



The development of the Keck Interferometer is managed by JPL for NASA's Office of Space Science, Washington, D.C. JPL is a division of the California Institute of Technology in Pasadena. The W.M. Keck Observatory is funded by Caltech, the University of California and NASA, and is managed by the California Association for Research in Astronomy, Kamuela, Hawaii.

Web Links

Keck Interferometer -- home page from JPL. See also the W.M. Keck Observatory home page at Caltech (external link)

Terrestrial Planet Finder -- this future space interferometry mission will look for infrared radiation from Earth-like planets orbiting other stars.

NASA Origins Program -- NASA's Origins Program seeks to answer two enduring human questions that we once considered around ancient campfires, yet still keep alive in today's classrooms: Where do we come from? Are we alone?

A Sharper View of the Stars -- Scientific American article explains the basics of optical interferometry. (external link)

Interactive Interferometry Demo -- A Shockwave application from the Space Interferometry Mission web site at JPL.

Playing Shell Games with Light -- constructive and destructive interference of light waves underpin the technique of optical interferometry


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