The hunt for extraterrestrial life is getting a major boost from revolutionary new technology that will give some of the world's largest telescopes the capability to detect Earth-size planets outside of our solar system, a feat not equaled even by the Hubble Space Telescope.

The technique, called interferometry, combines the light captured by several large telescopes to mimic a single giant telescope with enough power to detect a quarter on the moon from Earth.

"The goal is nothing less than finding the first ever Earth-like planet orbiting around a star," said planet hunter Geoff Marcy of the University of California at Berkeley. "We've never found one."

The smallest rocky planet detected to date has around four times the mass of Earth. This planet, as well as most of the 300 exoplanets discovered to date, have been detected by the "wobble" or shift in the light spectrum of the star caused by the slight gravitational tug of the orbiting planet. Another planet-hunting method, called gravitational microlensing, takes advantage of the way the gravity of an exoplanet's star bends and focuses the light from a more distant star like a lens. Small deviations in the light from the distant star indicate that a planet is orbiting the lensing star.

Interferometry will surpass both of these strategies in the search for smaller, earth-like worlds that orbit their star at a distance — in the "habitable zone" — that could harbor life. The technique involves incredibly precise measurements of the position of a star, so that the minutest wobble caused by the gravity of an orbiting planet 100,000 times smaller can be detected.

"It will be able to determine if a star budges a little bit as an Earth-like planet orbits that star," said Marcy, who is an expert in using the wobble technique, which can't detect very small planets. "The real holy grail of planet-hunting is to find other earths and ascertain whether they are habitable."

The array of telescopes in Chile's Atacama Desert collectively known as the Very Large Telescope Interferometer (VLTI) is currently being outfitted with an interferometry device called PRIMA. The technology will give the combined telescopes precision equivalent to the distance a human hair grows in a minute — 0.0003 millimeter — from 100 meters away.

"PRIMA will revolutionize exoplanet detection and our understanding of other solar systems," said Fred Kamphues, a telescope expert at Dutch company TNO, which built a key part of the device called the Star Separator.

The technology consists of many smaller mirrors, moved by pistons at precise levels smaller than an atom. The effect is to direct the light from each telescope into underground tunnels in such a way that the light waves from the star cancel each other out, revealing the faint light of an orbiting planet.

PRIMA has been tested on two of the four large telescopes in the array and will be installed on the two others as well as two smaller auxiliary telescopes. The combined system will start hunting for planets in about six months.

The VLTI, which is run by the European Southern Observatory, will be the most effective small-planet hunting telescope on Earth. The VLTI's four large telescopes have mirrors that are 27 feet across, currently among the largest in the world, but it could lead the planet-hunting pack even when new, much larger telescopes are built.

"I think that with the planned new facilities and future observatories under study, it is quite likely that we will find extraterrestrial life within the next 100 years," Kamphues said.

Marcy believes astronomy's future over the next century "is not to build ever larger mirrors, but to build smaller mirrors separated by large distances."

The United States had a big technological lead in interferometry earlier in the decade with plans to install a system to combine the light from the two 33-foot Keck telescopes and a surrounding array of six smaller telescopes on Mauna Kea in Hawaii. The project was supposed to be completed by 2004, but was stalled by funding cuts at NASA, allowing the Europeans to jump ahead.

"In effect, now the ball has been dropped," Marcy said. "There just isn't enough money right now."

Even more unfortunate for U.S. astronomers was the drying up of funds for the Space Interferometry Mission, an effort to launch into space twin telescopes, connected by a 20-foot-long aluminum arm that could function as an interferometer. SIM wouldn't be hampered by peering though the murk of Earth's atmosphere which would make it far more effective than ground-based systems.

A decade of work at NASA's Jet Propulsion Laboratory in Pasadena, California to design the planet-hunting space telescope is on hold indefinitely, leaving the scientists and engineers distraught. With the current economic situation, and the push to complete the Space Shuttle's replacement, it could be a very long time before the project comes to fruition.

"We're just dearly hoping that some time NASA will find the funding to build SIM," Marcy said. "It would literally be twenty times better than PRIMA."

It is hard to believe the mission won't be completed some day, however. The possibility that we could answer the ultimate question of whether we are alone in the universe is just too tantalizing.

"We can taste the answer to this question," Marcy said. "That is a quest the human spirit won't let go."

Loretta Hidalgo Whitesides contributed to this report.

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Photos: The Very Large Telescope Interferometer/TNO; Star Separator/TNO; Space Interferometry Mission/NASA