It used to be that planets were familiar places such as Mars and Saturn that orbited our sun and were well known to all schoolchildren.

Since astronomers identified the first planet outside our solar system 13 years ago, however, that idea has become downright quaint. Because now, according to the Extrasolar Planets Encyclopedia, there are 277 confirmed "extrasolar" planets, and quite a few more on the list of those suspected but not yet confirmed.

This explosion in planetary discoveries is taking place at such warp speed that even those most intimately involved are often amazed -- especially because their ultimate goal is nothing less than finding life elsewhere in the universe.

"This is an absolutely astounding time for this field," said Mark Swain of NASA's Jet Propulsion Laboratory, who last week reported finding the first "exoplanet" to have organic methane in its atmosphere.

"We're not only finding them rapidly and in great variety, but we're starting to characterize them -- their mass and orbits, the properties of their atmospheres, measurements of day and night, dynamics of their winds," he said after the methane discovery was released last week.

So far, most of the faraway planets are large, super-hot gas giants like Jupiter and Saturn, which are not expected to be able to support life. They are also so far away that humans are unlikely to ever directly observe them. The planet with methane is a very close one -- it would take a spaceship traveling at the speed of light 63 years to get there -- but most others are hundreds or thousands of light-years away.

But with astronomers regularly finding ingenious ways to locate and examine distant planets -- sometimes with new technologies, sometimes because of inventive new ways of analyzing data -- many in the field say it is just a matter of time before they detect Earth-size, rocky planets elsewhere in the cosmos.

"We've already been able to detect planets with only five or 10 times the mass of the Earth," said Sara Seager, a prominent extrasolar planet researcher and professor at the Massachusetts Institute of Technology. The large gas giants typically are hundreds of times more massive than our planet. "If the technology improves a bit, with another push, we'll find Earths," she said.

This is not to say that scientists will necessarily find life on another distant planet -- although that is certainly the hope and, to some extent, the expectation. But with the now-proven ability to detect molecules of methane, a chemical often associated with life, researchers are becoming more confident that they will be able to detect signs of biological activity in faraway solar systems if it exists.

"Finding methane in the atmosphere of a particular exoplanet is very important, but demonstrating that we have the tools to identify molecules in these atmospheres is of even greater significance," said Seager, who was not involved in the study.

Carl B. Pilcher, director of the NASA Astrobiology Institute at the Ames Research Center in California, agrees that the big challenge now is to detect smaller, Earth-size planets, then to find more and better ways to learn about their atmospheres and other characteristics.

He said that just as the exoplanet search has become supercharged of late, so, too, has the search for life on other planets and in other solar systems, which is the primary focus of the institute.

"There are a hundred billion stars in our galaxy and probably a hundred billion other galaxies with as many stars as ours, so it seems highly unlikely that there are not Earth-like planets orbiting some of them out there, waiting to be discovered," he said. "With that in mind, we're working hard on techniques to answer the question of whether there's life on them to be found."

Some of the work of finding exoplanets and analyzing their orbits and atmospheres is being done with ground-based telescopes, and some from orbiting observatories such as the Hubble Space Telescope, which provided the data used to discover exoplanet methane. In addition, astronomers and astrophysicists are developing ever more powerful ways to interpret data and to use spectroscopy, which splits light into its components to reveal the "fingerprints" of various chemicals.

Considerably more powerful hardware is also on the way. NASA's Kepler satellite, which is designed to find distant planets as they transit in front of their stars, is supposed to be launched next spring and is expected to locate hundreds or thousands of new planets. The James Webb Space Telescope, a high-powered Hubble successor that will be able to find atmospheric molecules in rocky exoplanets rather than only in gas giants, is scheduled for launch in 2013.

The recent discovery of methane in the atmosphere of exoplanet HD 189733b was the kind of breakthrough that the astrobiology institute and many others are looking for -- even though the methane almost certainly has chemical origins, as on Jupiter and Saturn, rather than biological ones. (The planet is punishingly close to its sun -- making a full orbit in two days -- and has an atmospheric temperature of about 1,700 degrees Fahrenheit.) Nonetheless, methane can be a byproduct of biological processes, and so learning how to detect it is essential.

The observations were made as the planet passed in front of its parent star in what astronomers call a transit.

As the light from the star briefly pierced the atmosphere along the planet's edge, atmospheric gases imprinted their identifiable signatures on the starlight.

The astronomers expected to find signs of carbon monoxide on the spectrogram rather than methane, and they were surprised by what they found.

"This indicates we don't really understand exoplanet atmospheres yet," Swain said.

But considering that 15 years ago not a single planet had been discovered outside our solar system, Swain said, it is remarkable that scientists are now probing the makeup and dynamics of planets so far away.

"I think the more we look, the more evidence we'll find that the conditions are out there for life to exist," he said. "I don't see a good reason why our situation in our solar system should be unique. Perhaps uncommon, but not unique."

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