2014/04/30 by Timothy D. Brandt, David S. Spiegel · 1 citation
Physics and Astronomy · #astro-ph.EP #astro-ph.IM
paper · pdf · doi:10.1073/pnas.1407296111
published as Proceedings of the National Academy of Sciences, September 16, 2014, vol. 111, issue 37, pp. 13278-13283 · PNAS published, replaced with accepted version. Conclusions mostly unchanged, 5 page supporting information added
arxiv created 2014/09/25 · arxiv updated 2014/09/29
The goal of finding and characterizing nearby Earth-like planets is driving many NASA high-contrast flagship mission concepts, the latest of which is known as the Advanced Technology Large-Aperture Space Telescope (ATLAST). In this article, we calculate the optimal spectral resolution R=λ/δλ and minimum signal-to-noise ratio per spectral bin (SNR), two central design requirements for a high-contrast space mission, in order to detect signatures of water, oxygen, and chlorophyll on an Earth twin. We first develop a minimally parametric model and demonstrate its ability to fit synthetic and observed Earth spectra; this allows us to measure the statistical evidence for each component's presence. We find that water is the easiest to detect, requiring a resolution R \gtrsim 20, while the optimal resolution for oxygen is likely to be closer to R = 150, somewhat higher than the canonical value in the literature. At these resolutions, detecting oxygen will require ∼2 times the SNR as water. Chlorophyll requires ∼6 times the SNR as oxygen for an Earth twin, only falling to oxygen-like levels of detectability for a low cloud cover and/or a large vegetation covering fraction. This suggests designing a mission for sensitivity to oxygen and adopting a multi-tiered observing strategy, first targeting water, then oxygen on the more favorable planets, and finally chlorophyll on only the most promising worlds.