Finding planets outside of our solar system has become a regular occurrence. They’ve been found orbiting pulsars, multiple star systems (binary, trinary and even quaternery), red dwarfs, giants and white dwarfs.
However one of the more difficult parts of finding exo-planets has been determining the composition of their atmospheres (or if they have any at all).
Certain assumptions can be made from the size of the planet. Something twice the size of jupiter is most likely to be a gas giant, while something maybe five times the size of earth is more likely to be a rocky planet. However if you want to know about the atmosphere of the planet, then you’re going to need to analyse the light that it reflects.
This of course tends to be a bit of a problem with mainline stars like our own. They’re big, bright and tend to overwhelm the dull light reflected off the surface or atmosphere of the planet. Which is why Abraham Loeb from Harvard University and Dan Maoz of Tel Aviv University have proposed a search program that will focus on the smaller, duller white dwarf stars.
In this paper (PDF - Detecting bio-markers in habitable-zone earths transiting white dwarfs) they outline the proposal to focus on a sample of five hundred white dwarf stars, looking for the tell tale signs of transiting planets. Once they find such an event they want to use the soon to be launched James Webb Space Telescope (the successor to both the Hubble and Spitzer Space Telescope) to capture the light reflected off the atmosphere or surface of the planet (and not swamped by the light of the star) so they analyse it for the signs of water, carbon dioxide, and most importantly in the search for habital planets, oxygen.