Work

Detecting and Constraining N2abundances in Planetary Atmospheres Using Collisional Pairs

Year: 2015

Type: article

Abstract: Characterizing the bulk atmosphere of a terrestrial planet is important for determining surface pressure and potential habitability. Molecular nitrogen (N 2 ) constitutes the largest fraction of Earth's atmosphere and is likely to be a major constituent of many terrestrial exoplanet atmospheres. Due to its lack of significant absorption features, N 2 is extremely difficult to remotely detect. However, N 2 produces an N 2 –N 2 collisional pair, (N 2 ) 2 , which is spectrally active. Here we report the detection of (N 2 ) 2 in Earth's disk-integrated spectrum. By comparing spectra from NASA's EPOXI mission to synthetic spectra from the NASA Astrobiology Institute's Virtual Planetary Laboratory three-dimensional spectral Earth model, we find that (N 2 ) 2 absorption produces a ∼35% decrease in flux at 4.15 μ m. Quantifying N 2 could provide a means of determining bulk atmospheric composition for terrestrial exoplanets and could rule out abiotic O 2 generation, which is possible in rarefied atmospheres. To explore the potential effects of (N 2 ) 2 in exoplanet spectra, we used radiative transfer models to generate synthetic emission and transit transmission spectra of self-consistent N 2 –CO 2 –H 2 O atmospheres, and analytic N 2 –H 2 and N 2 –H 2 –CO 2 atmospheres. We show that (N 2 ) 2 absorption in the wings of the 4.3 μ m CO 2 band is strongly dependent on N 2 partial pressures above 0.5 bar and can significantly widen this band in thick N 2 atmospheres. The (N 2 ) 2 transit transmission signal is up to 10 ppm for an Earth-size planet with an N 2 -dominated atmosphere orbiting within the habitable zone of an M5V star and could be substantially larger for planets with significant H 2 mixing ratios.

Source: The Astrophysical Journal

DOI: 10.1088/0004-637x/810/1/57

Authors: Edward W. Schwieterman, Tyler D. Robinson, Victoria S. Meadows, Amit Misra, Shawn Domagal-Goldman

Institutions: NASA Astrobiology Institute, University of Washington, Ames Research Center, Goddard Space Flight Center

Language: English

Topic: Stellar, planetary, and galactic studies

Subfield: Astronomy and Astrophysics

Field: Physics and Astronomy

Domain: Physical Sciences

Open Access status: bronze

Funders: National Aeronautics and Space Administration, University of Washington, NASA Astrobiology Institute, Ames Research Center

Awards: G3274742622, FPDS BASE DESCRIPTION, MULTIPLE YEAR AWARD&INCREMENTAL FUNDING FOR YEARS 1 OF 5. THIS PROPOSAL IS ENTITLED, "THE VIRTUAL PLANETARY LABORATORY." THI, G465804250, G855615703