Planets around White Dwarfs could be the first to reveal bio-markers

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An outline of the paper: Detecting bio-markers in habitable-zone earths transiting white dwarfs, by Loeb & Maoz

Detecting bio-markers in the atmospheres of planets that orbit main-sequence stars like the Sun is extremely challenging, Abraham Loeb and Dan Maoz, from the Universities of Harvard and Tel-Aviv, suggest that White Dwarfs are far better suited to atmospheric studies and could allow us to detect molecular oxygen.

White Dwarfs have previously been proposed as ideal targets for Earth-sized planet searches since they are much smaller than main-sequence stars and would provide a bigger relative dip in flux when planets transit them. In principle, the same idea can be applied to atmospheric observations: a larger percentage of star light would pass through the atmosphere of the planet, making molecular signals much easier to extract.

White Dwarfs have long-lived habitable zones by virtue of their long cooling timescale, so a planet orbiting a White Dwarf has plenty of time to develop life. Molecular oxygen only began to accumulate in the Earth’s atmosphere after life began: detecting it in the atmosphere of another planet could be a sign that there is life there too.

Loeb and Maoz calculate that the James Webb Space Telescope (JWST), due for launch in 2018, will be capable of detecting molecular oxygen in the atmospheres of planets orbiting White Dwarfs after just over five hours of exposure time.

A drawback to this proposal is the current lack of White Dwarf planet discoveries. Assuming that there is an Earth-mass planet orbiting one in every three White Dwarfs, the odds of us actually seeing a transit is just one in five-hundred. These odds look long, however we have plenty of time to get searching – JWST won’t launch until 2018, and five years is a long time in the field of exoplanets. Plus, an up-coming parallax mission, Gaia, will significantly improve our chances.

Detecting molecular Oxygen in the atmosphere of any extra-solar planet would be a huge forward leap for astronomy, so Loeb and Maoz’s idea may be well worth pursuing despite the long-sounding odds.

Feature image: NASA, ESA and G. Bacon (STScI)

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About Author

I am a recent addition to the exoplanet research team at Oxford University. I work closely with Kepler data to pin down stellar rotation rates which can be used to date stars and planets, giving us clues about planetary formation processes. My supervisor is Dr Suzanne Aigrain.