PSJC #189 April 10 2015
False Positive Biosignatures in Exoplanetary Atmospheres
We will discuss a paper by
Rein, Fujii, and Spiegel (2014)
that was published last year in PNAS.
An arXiv version of the
paper is available.
The abstract is as follows:
The detection of strong thermochemical disequilibrium in the atmosphere
of an extrasolar planet is thought to be a potential biosignature. In
this article we present a previously unidentified kind of false positive
that can mimic a disequilibrium or any other biosignature that involves
two chemical species. We consider a scenario where the exoplanet hosts
a moon that has its own atmosphere and neither of the atmospheres is in
chemical disequilibrium. Our results show that the integrated spectrum
of the planet and the moon closely resembles that of a single object in
strong chemical disequilibrium. We derive a firm limit on the maximum
spectral resolution that can be obtained for both directly imaged and
transiting planets. The spectral resolution of even idealized space-based
spectrographs that might be achievable in the next several decades is
in general insufficient to break the degeneracy. Both chemical species
can only be definitively confirmed in the same object if absorption
features of both chemicals can be unambiguously identified and their
combined depth exceeds 100%.