A. R. Belu, F. Selsis, S. N. Raymond, E. Pallé, R. A. Street, D. K. Sahu, K von Braun, E. Bolmont, P. Figueira, G. C. Anupama, I. Ribas

Abstract
Given the very close proximity of their habitable zones, brown dwarfs represent high-value targets in the search for nearby transiting habitable planets that may be suitable for follow-up occultation spectroscopy. In this paper we develop search strategies to find habitable planets transiting brown dwarfs depending on their maximum habitable orbital period (P_{HZ out}). Habitable planets with P_{HZ out} shorter than the useful duration of a night (e.g. 8-10 hrs) can be screened with 100% completeness from a single location and in a single night (near-IR). More luminous brown dwarfs require continuous monitoring for longer duration, e.g. from space or from a longitude-distributed network (one test scheduling achieved - 3 telescopes, 13.5 contiguous hours). Using a simulated survey of the 21 closest known brown dwarfs (within 7 pc) we find that the probability of detecting at least one transiting habitable planet is between 4.5^+5.6/_-1.4 and 56⁺³¹/_-13 %, depending on our assumptions. We calculate that brown dwarfs within 5-10 pc are characterizable for potential biosignatures with a 6.5 m space telescope using ~1% of a 5-year mission’s lifetime spread over a contiguous segment only 1/5^th to 1/10^th of this duration.

Keywords
astrobiology — brown dwarfs — eclipses — infrared: planetary systems — instrumentation: spectrographs — solar neighborhood

The Astrophysical Journal
Volume 768, Number 2, Page 125_1
2013 May

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