A NASA space telescope for the first time has identified molecules in the atmospheres of worlds outside our solar system.
Recent observations indicate that two giant gas planets trillions of miles away are cloudier and drier than theorists had predicted.
However, just as important as the unprecedented scientific data is the potential the discovery holds for eventually finding life on distant Earth-like bodies.
"These results are a very important steppingstone for our ultimate goal of characterizing planets around other stars where life could exist," said Mark R. Swain, a research scientist at NASA's Jet Propulsion Laboratory in La Canada Flintridge. "The results you're seeing today are really a dress rehearsal for what we're looking forward to in the future."
The discovery was made using information collected by NASA's Spitzer Space Telescope, a $670-million observatory launched from Cape Canaveral in 2003.
Like its sister spacecraft, the Hubble Space Telescope, Spitzer is one of the agency's four "great observatories" that survey the cosmos with sophisticated instruments from a clear vantage point beyond Earth's atmosphere.
Spitzer follows our planet in an orbit around the sun.
Unlike Hubble, most of Spitzer's most important observations are made by using infrared light, which is not visible to the human eye. By separating the light emitted by a distant planet into different wavelengths, astronomers can determine the object's chemical composition.
Spitzer recently turned its powerful telescope on a pair of planets called "hot Jupiters" because they are similar to the giant gaseous world in our solar system but travel in orbits much closer to their stars. Though more than 200 planets have been discovered outside our solar system, these two are among nine that can be analyzed in this way.
One planet, designated HD 189733b, is slightly larger than Jupiter and lies 370 trillion miles away in the constellation Vulpecula.
The other, HD 209458b, is about a third larger than Jupiter and sits 904 trillion miles away in the constellation Pegasus -- a distance so vast it takes light from the planet 150 years to reach Earth.
Scientists were stunned when Spitzer failed to detect water in the atmosphere of either world. What the telescope found instead raised new questions about the planet in the Pegasus constellation.
"We see sand-like silicate dust and evidence of carbon-based molecules that are essentially what you get when you burn stuff," said Joseph Harrington, a physics professor at the University of Central Florida who is a member of one of three research teams involved in the discovery.
Some scientists have speculated that dusty, high-altitude clouds unlike anything found in our solar system could make it difficult to detect water in the planets' atmospheres.
The broader goal of finding life on faraway worlds has been given a boost by the discoveries, which were announced Wednesday and will be published in today's edition of the journal, Nature. Some of the same tools and techniques could be used one day to examine rocky, Earth-like planets for signs of biological activity.