A planet the size of Jupiter outside our solar system contains water, a new study suggests.
The findings, published in The Astrophysical Journal Letters, describes how a new technique detected water on a planet orbiting the nearby star, Tau Boötis. While water has been detected on a handful of other planets, this study is the first to use the radial velocity technique, which allowed researches to study the molecules that make up the planet’s atmosphere.
"Planets like [Tau Boötis b], which are as massive as Jupiter but much hotter, do not exist in our solar system. Our detection of water in the atmosphere of Tau Boötis b is important because it helps us understand how these exotic hot-Jupiter planets form and evolve. It also demonstrates the effectiveness of our new technique, which detects the infrared radiation in the atmospheres of these planets," Chad Bender, a research associate in the Penn State Department of Astronomy and Astrophysics and a co-author of the paper, said in a statement.
Other techniques to detect water on exoplanets required the planet to either orbit its host star or be significantly far away from it. A significant portion of exoplanets didn't fit either of these criteria. The latest study used an infrared technique that allowed the atmospheres exoplanets to be studied.
"We now are applying our effective new infrared technique to several other nontransiting planets orbiting stars near the Sun," Bender said. "These planets are much closer to us than the nearest transiting planets, but largely have been ignored by astronomers because directly measuring their atmospheres with previously existing techniques was difficult or impossible."
The radial velocity technique helps determine the motion of a star from its gravitational pull of its orbiting planet. Using data from Tau Bootis b from the Near Infrared Echelle Spectrograph in Hawaii, researchers were able to compare the molecular signature of the water to the light spectrum emitted by the planet.
"The information we get from the spectrograph is like listening to an orchestra performance; you hear all of the music together, but if you listen carefully, you can pick out a trumpet or a violin or a cello, and you know that those instruments are present," Alexandra Lockwood, the first author of the study, said in a statement. "With the telescope, you see all of the light together, but the spectrograph allows you to pick out different pieces; like this wavelength of light means that there is sodium, or this one means that there's water."
The method also allows researchers to determine the mass of the star.
"When you're doing calculations to look for the atmospheric signature -- which tells you that there's water present -- you also determine the 3-D motion of the star and the planet in the system. With this information, if you also know the mass of the star, you can determine the mass of the planet," Lockwood said.
The new technique may help astronomers examine the atmospheres of other planets that are cooler and more distant to their host stars -- environments that are more favorable to house H20.
"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," Geoffrey Blake, Caltech professor of cosmochemistry and planetary sciences and professor of chemistry, said. "Future telescopes such as the James Webb Space Telescope and the Thirty Meter Telescope 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."