A calculated methane line list for characterizing exoplanets and brown dwarfs

The discovery of over 400 orbiting other stars has opened a whole new field of astronomy. Astronomers are now beginning to ask questions about these new worlds: what are they like? what are they made of? and of course, are there any signs of life? Characterizing these exoplanets, as they are called, requires the use novel observational techniques as it is rarely possible to separate the planet from its nearby and very bright parent star. It transpires that about 70 of the planets detected so far pass in front of their star when viewed from earth. Observation of the slight dimming of the star for different colours of light is beginning to yield valuable information on the composition of exoplanets. However to do understand these observations requires building atmospheric models to simulate how the planet interacts with the light coming from the planet's parent star. This is in turn requires huge quantities of laboratory data. However in many cases the laboratory data required is often simply not available; this is particularly true for the most commonly observed class of exoplanets 'hot Jupiters', which are gas giant planets who orbit close to their parent star. It is also true for similar studies of brown dwarfs and cool stars. The most glaring omission in all this work is reliable data for methane. Methane has been detected in exoplanets and is a major atmospheric species in brown dwarfs and cool carbon stars. However models of these and other astronomical objects are hampered by the lack of laboratory data on methane. How a molecule such as methane absorbs and emits light is very complicated since, particularly at elevated temperatures, it requires knowledge of the position and strength of probably many billions of individual transition lines. This proposal will use first principles quantum mechanical calculations to provide a comprehensive and reliable rotation-vibration line list for methane. These calculations will be compared with the much more limited available laboratory studies of the problem, which will if necessary be used to help improve the accuracy of the resulting computed line list. The new line list will allow astronomers and other scientists to model how methane absorbs or emits light as a function of temperature. This line list will be made widely available via a new web portal, www.exomol.com, and using other web-based distribution methods methods.