Astronomers led by Alexandra Lockwood from California Institute of Technology in Pasadena have detected the water vapor in the atmosphere of an extrasolar planet circling the nearby star Tau Boötis.
This is an artist’s impression of Tau Boötis b. Image credit: David Aguilar / Harvard-Smithsonian Center for Astrophysics.
The alien world, known as Tau Boötis b, Tau Boötis Ab or the Millennium Planet, was discovered in 1996. It is a so-called hot-Jupiter that orbits closely around its host star every 3 days 7.5 hours.
Located in the constellation of Boötes, around 51 light-years away from our planet, Tau Boötis b has a mass almost six times that of Jupiter.
“Planets like Tau Boötes b, which are as massive as Jupiter but much hotter, do not exist in our Solar System,” said Dr Chad Bender from Penn State University, who is a co-author of the paper published in the Astrophysical Journal Letters (arXiv.org).
“Our detection of water in the atmosphere of Tau Boötes 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.”
Scientists previously had detected water vapor on a handful of other planets, using a technique that works only if a planet has an orbit that passes it in front of its star, when viewed from Earth.
A map of the constellation Boötes. The exoplanet Tau Boötes b orbits the star Tau Boötes, which is indicated by the red circle. Image credit: International Astronomical Union / Sky and Telescope Magazine.
Scientists also were able to use another imaging technique that works only if the planet is sufficiently far away from its host star. However, significant portions of the population of extrasolar planets do not fit either of these criteria, and there had not been a way to discover information about the atmospheres of these planets.
“We now are applying our effective new infrared technique to several other nontransiting planets orbiting stars near the Sun,” Dr 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.”
With the new detection technique and more-powerful future telescopes such as the James Webb Space Telescope and the Thirty Meter Telescope, Dr Bender with colleagues expect to be able to examine the atmospheres of planets that are much cooler and more distant from their host stars, where liquid water is even more likely to exist.
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Alexandra C. Lockwood et al. 2014. Near-IR Direct Detection of Water Vapor in Tau Boötis b. ApJ 783, L29; doi: 10.1088/2041-8205/783/2/L29
