The characterization of the atmospheres of habitable-zone Earth-mass exoplanets that transit across main-sequence stars, let alone the detection of bio-markers in their atmospheres, will be challenging even with future facilities. It has been noted that white dwarfs (WDs) have long-lived habitable zones and that a large fraction of WDs may host planets.
We point out that during a transit of an Earth-mass planet across a WD, the planet's atmospheric transmission spectrum obtains a much higher contrast over the stellar background compared to a main-sequence host, because of the small surface area of the WD. The most prominent bio-marker in the present-day terrestrial atmosphere, molecular oxygen, is readily detectable in a WD transit via its A-band absorption at ~0.76 micron.
A potentially life-sustaining Earth-like planet transiting a WD can be found by assembling a suitable sample of ~500 WDs and then surveying them for transits using small telescopes. If and when such a transiting case is found, the O_2 absorption in the planetary atmospheric transmission spectrum would be detectable with the James Webb Space Telescope (JWST) in about 5 hours of total exposure time, integrated over 160 2-minute transits. Characterization of the planet atmosphere using other tracers such as water vapour and CO_2 will be considerably easier. We demonstrate this future discovery space by simulating a possible transmission spectrum that would be obtained with JWST.
Abraham Loeb, Dan Maoz
(Submitted on 21 Jan 2013 (v1), last revised 24 Aug 2013 (this version, v3))
Comments: erroneous factor pi/2 corrected in Eq. 1
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:1301.4994 [astro-ph.EP]
(or arXiv:1301.4994v3 [astro-ph.EP] for this version)
From: Dan Maoz
[v1] Mon, 21 Jan 2013 21:00:00 GMT (78kb)
[v2] Tue, 19 Feb 2013 14:50:56 GMT (80kb)
[v3] Sat, 24 Aug 2013 09:52:48 GMT (80kb)
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