Water Detected in the Atmosphere of a Hot Jupiter Exoplanet!

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Astronomer's have been measuring the molecular chemistry of exoplanet atmospheres for more than a decade.  But most of those detections require a very specific geometry that requires a planet to pass in front of a star, as viewed from Earth, (commonly referred to as "transiting") so the total number of planets that have been probed is still very small.

Today, colleagues and I announced the detection of water in an exoplanet that does not transit its parent star.  tau Boötis b is a gaseous planet that is slightly larger than Jupiter, has a surface temperature of more than 2000 degrees Fahrenheit, and orbits its parent star in just over three Earth days!  Our solar system does not possess any planets remotely similar to this, and so understanding how these planets form and evolve is very difficult. 

An artist's conception of a hot-Jupiter extrasolar planet orbiting a star similar to tau Boötes. Credit: Image used with permission of David Aguilar, Harvard-Smithsonian Center for Astrophysics

Our measurement of water in the atmosphere of tau Boötis b helps to constrain the chemical and physical processes that occur in the planet's atmosphere. At the same time, it allowed us to "weigh" the planet, using Kepler's Laws to determine its mass.  

We used the NIRSPEC spectrograph on the Keck II telescope, located on Mauna Kea in Hawaii to obtain high resolution spectroscopy of the planet and measure the water in the spectrum.  This measurement was exceedingly difficult because the planet is about 10,000 times fainter than its parent star, but they are so close together on the sky that the data we received at the telescope contains the blended light from both the planet and the star. 

Only after advanced processing were we able to separate out the planet's signal.
This difficult endeavour was carried out by Caltech graduate student Alexandra Lockwood and Penn State graduate student Alexander Richert.  Also integral were John Carr, from the Naval Research Lab, and Travis Barman, from the University of Arizona, who provided computer models of the star and planet spectra, and Geoff Blake & John Johnson who provided access to the Keck Observatories

You can access the full paper, which appeared in The Astrophysical Journal Letters on February 24, 2014.

If you can't get through the paywall, download the pre-print from arXiv.org.

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