For the first time, a team of American astronomers has used near-infrared spectroscopy to directly detect water vapor in the atmosphere of a gas giant planet in close orbit around Tau Bootis — a bright star in Bootes that may have even helped Odysseus home from Troy.
But not even Odysseus could have imagined that 21st century spectroscopy would be teasing data from the hellishly hot atmosphere of a 3.8 Jupiter-mass planet around a star only 50 light years from earth.
Water has been detected in the atmospheres of several extrasolar planets using other techniques. However, this detection via thermal emission, as reported in The Astrophysical Journal Letters, enables astronomers to directly characterize the atmospheres of such “hot Jupiters.”
“This discovery of water on Tau Bootis b is absolutely wonderful,” said longtime extrasolar planet hunter Geoff Marcy, an astronomer at the University of California at Berkeley, who along with astronomer Paul Butler, first discovered the planet in 1996.
And it’s all the more “incredible,” says Marcy, considering that only 18 years ago, he and colleagues still thought it “a miracle” to be able to indirectly detect any such extrasolar Jupiter-mass planets, much less study their atmospheres.
Penn State University astronomer Chad Bender, one of the paper’s co-authors, says this is the first time anyone has detected water in a non-transiting planet. That is, a planet having its atmosphere probed by the background glow from its parent star.
That’s important, says Bender, because the population of non-transiting extrasolar planets is much larger than those that from our line of sight appear to transit across the face of their parent stars.