Astronomers have said that they, or at least their telescopes, have laid eyes for the first time on planets beyond the solar system.
Using the NASA Spitzer Space Telescope and careful timing, two different teams studying two different planets were able to distinguish the glow of the planets' infrared radiation from the overwhelming glare of their parent stars. Both planets are so-called hot Jupiters, massive bodies circling their stars in tight, blowtorching orbits and probably unfit for the kind of life found on Earth.
Previously, astronomers could infer the existence and some properties of these and other so-called exoplanets only by indirect means. They said directly measuring light from the planets was a major step in the quest toward understanding what alien planets are made of, because different molecules in the atmosphere absorb infrared light in characteristic ways and will allow scientists to compare these alien planets with those in the solar system. Ultimately, astronomers would like to know if Earth, with its ability to evolve and support life, is unique or common in the universe.
David Charbonneau of the Harvard-Smithsonian Center for Astrophysics, who led one of the teams, said he was ecstatic when he first saw the data. "We've been hunting for this light for almost 10 years, ever since extrasolar planets were first discovered," Charbonneau said.
The Harvard-Smithsonian team and the other team, led by L. Drake Deming of the Goddard Space Flight Center, announced the results at a news conference at the headquarters of the National Aeronautics and Space Administration in Washington. The Deming team's paper was published online Tuesday by the journal Nature; the other team will publish its results in The Astrophysical Journal on June 20.
Geoffrey Marcy, a planet hunter at the University of California, Berkeley, called the results "the stuff of history books" and added, "With this result, we are closer to understanding our own human roots, chemically, among the stars."
Alan Boss, a planetary theorist at the Carnegie Institution of Washington, said in an e-mail message that the discoveries showed "that we are well along the way to combining astronomy and biology into the new science of astrobiology, with the ultimate goal being to search for life beyond Earth."
About 130 planets are known to orbit other stars, but until now they have all been detected indirectly, either through the wobble their gravity induced in the motions of their parent stars or through slight dips in the stars' light when their planets passed in front of them.
The planets whose discoveries were reported Tuesday fall in the latter category, passing directly in front of their parent stars periodically and then behind them. The Goddard team's object, known as HD 209458b, was the first planet detected by the so-called transit method, back in 1999. It circles a star about 153 light-years away in the constellation Pegasus, making a complete trip every 3.5 days. In 2001, Charbonneau used the Hubble Space Telescope to make spectroscopic measurements of this star while the planet was passing in front of it and found that sodium and hydrogen were present in the planet's atmosphere.
The other planet, known as TrES-1 after the telescope network that discovered it, the Trans-Atlantic Exoplanet Survey, is about 500 light-years away in the constellation Lyra. Discovered last year by a telescope only four inches, or 10 centimeters, in diameter, it circles its parent every three days.
In both cases the astronomers were able to use the special geometry of these planetary systems to tease out the faint light of each planet from its parent's glare, comparing measurements made while the planet and star were both visible and while the planet was hidden behind the star.