Exoplanet Orbiting Tau Bootis Star Could Have Watery Atmosphere

Lee Rannals for redOrbit.com – Your Universe Online

Astronomers, publishing a paper in The Astrophysical Journal Letters, say they may have discovered water on an exoplanet outside our solar system.

The team of scientists say they believe they have detected water in the atmosphere of a planet orbiting the nearby star tau Boötis.

“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,” 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. “It also demonstrates the effectiveness of our new technique, which detects the infrared radiation in the atmospheres of these planets.”

Previously, scientists detected water vapor by using a technique that only works if a planet transits in front of its star when viewed from Earth. However, the team applied a new infrared technique to help make the latest discovery.

“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,” Bender said.

The team used high-resolution L-band spectroscopy to measure the radial velocity variations of the hot Jupiter in the tau Boötis planetary system.

“Treating the tau Boo system as a high flux ratio double-lined spectroscopic binary permits the direct measurement of the planet’s true mass as well as its atmospheric properties,” the astronomers wrote in the journal. “After removing telluric absorption and cross-correlating with a model planetary spectrum dominated by water opacity, we measure a 6-sigma detection of the planet.”

“This radial velocity leads to a planetary orbital inclination of i = 45+3-4degrees and a mass of M_P = 5.90+0.35-0.20 M_ Jup. We report the first detection of water vapor in the atmosphere of a non-transiting hot Jupiter, tau Boo b,” the team said.

The astronomers believe that this new technique used with more-powerful future telescopes could help examine the atmospheres of planets that are much cooler and more distant from their host stars. NASA’s upcoming James Webb Telescope is one of the future instruments that could help astronomers unveil these secrets within exoplanets in the future.