Researchers at Caltech and several other institutions have used a new technique to analyze the gaseous atmospheres of such extrasolar planets and have made the first detection of water in the atmosphere of the Jupiter-mass planet orbiting the nearby star Tau Booetis.

With further development and more sensitive instruments, this technique could help researchers learn about how many planets with water — like Earth — exist within our galaxy.

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Although the technique promises to augment how planetary scientists analyze the properties of extrasolar planets, it has limitations, the researchers say.

For example, the technique is presently limited to so-called “hot Jupiter” gas giant planets like Tau Booetis b — those that are large and orbit very close to their host star.

“The technique is limited by the light-collecting power and wavelength range of the telescope, and even with the incredible collecting area of the Keck mirror on the high, dry summit of Mauna Kea we can basically only analyze hot planets that are orbiting bright stars, but that could be expanded in the future as telescopes and infrared spectrographs improve,” Lockwood says.

In the future, in addition to analyzing cooler planets and dimmer stars, the researchers plan to continue looking for and analyzing the abundance of other molecules that might be present in the atmosphere of Tau Booetis b.

“While the current state of the technique cannot detect Earth-like planets around stars like the Sun, with Keck it should soon be possible to study the atmospheres of the so-called ‘super-Earth’ planets being discovered around nearby low-mass stars, many of which do not transit,” Blake says.

“Future telescopes such as the James Webb Space Telescope and the Thirty Meter Telescope (TMT) will enable us to examine much cooler planets that are more distant from their host stars and where liquid water is more likely to exist.”

The findings appear in the Astrophysical Journal Letters in a paper titled “Near-IR Direct Detection of Water Vapor in Tau Booetis b.”