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Published February 15, 2021 | Version v1
Journal article Open

Finding Signs of Life in Transits: High-Resolution Transmission Spectra of Earth-like Planets around FGKM Host Stars

  • 1. Carl Sagan Institute and Department of Astronomy, Cornell University, Ithaca, NY 14853, USA
  • 2. Carl Sagan Institute and Department of Astronomy, Cornell University, Ithaca, NY 14853, USA; Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA

Description

Thousands of transiting exoplanets have already been detected orbiting a wide range of host stars, including the first planets that could potentially be similar to Earth. The upcoming Extremely Large Telescopes and the James Webb Space Telescope will enable the first searches for signatures of life in transiting exoplanet atmospheres.

Here, we quantify the strength of spectral features in transit that could indicate a biosphere similar to the modern Earth on exoplanets orbiting different host stars (F0 to M8) with effective temperatures between 2,500 and 7,000K. The atmospheric biosignature pairs O+ CHand O3 + CH4 – which identify Earth as a living planet – are most prominent for Sun-like and cooler host stars in transit spectra of modern Earth analogs. For hotter host stars, refraction and a decreased CHconcentration significantly reduce the strength of CH4 spectral features. Many other chemical species, such as H2O and CO2, also possess strong spectral features between 0.4 μm and 20 μm. Transit depths vary between about 6,000 ppm (M8 host) to 30 ppm (F0 host) due to the different sizes of the host stars.

All high-resolution transit spectra and model profiles are available online: They provide a tool for observers to prioritize exoplanets for transmission spectroscopy, test atmospheric retrieval algorithms, and optimize observing strategies to find life in the cosmos.

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