Earth as an Exoplanet. II. Earth's Time-variable Thermal Emission and Its Atmospheric Seasonality of Bioindicators

Abstract

We assess the dependence of Earth's disk-integrated mid-infrared thermal emission spectrum on observation geometries and investigate which and how spectral features are impacted by seasonality on Earth. We compiled an exclusive dataset containing 2690 disk-integrated thermal emission spectra for four different full-disk observing geometries (North & South Pole centered and Africa & Pacific centred equatorial views) over four consecutive years. The spectra were derived from 2378 spectral channels in the wavelength range from 3.75 to 15.4 micron (nominal resolution $\approx$ 1200) and were recorded by the Atmospheric Infrared Sounder aboard the Aqua satellite. We learned that there is significant seasonal variability in Earth's thermal emission spectrum, and the strength of spectral features of bio-indicators, such as N2O, CH4, O3 and CO2 depends strongly on both season and viewing geometry. In addition, we found a strong spectral degeneracy with respect to the latter two indicating that multi-epoch measurements and time-dependent signals may be required in order to fully characterize planetary environments. Even for Earth and especially for equatorial views, the variations in flux and strength of absorption features in the disk-integrated data are small and typically $\le$ 10%. Disentangling these variations from the noise in future exoplanet observations will be a challenge. However, irrespectively of when the planet will be measured (i.e., day or night or season) the results from mid-infrared observations will remain the same to the zeroth order which is an advantage over reflected light observations.

arXiv comment21 pages, 15 Figures, 3 Tables

References in corpus (45)

• HEALPix -- a Framework for High Resolution Discretization, and Fast Analysis of Data Distributed on the Sphere
• The James Webb Space Telescope
• Habitable Zones Around Main-Sequence Stars: New Estimates
• A terrestrial planet candidate in a temperate orbit around Proxima Centauri
• Exoplanet Biosignatures: A Review of Remotely Detectable Signs of Life
• Biosignatures from Earth-Like Planets Around M Dwarfs
• Terrestrial Planet Occurrence Rates for the Kepler GK Dwarf Sample
• A temperate rocky super-Earth transiting a nearby cool star
• Exploring Exoplanet Populations with NASA's Kepler Mission
• Alien Maps of an Ocean-Bearing World
• The Detectability and Characterization of the TRAPPIST-1 Exoplanet Atmospheres with JWST
• Characterization of extrasolar terrestrial planets from diurnal photometric variability
• Exoplanet Biosignatures: A Framework for Their Assessment
• Stellar and Planetary Properties of K2 Campaign 1 Candidates and Validation of 17 Planets, Including a Planet Receiving Earth-like Insolation
• Effect of UV Radiation on the Spectral Fingerprints of Earth-like Planets Orbiting M dwarfs
• Disequilibrium biosignatures over Earth history and implications for detecting exoplanet life
• Detecting Oceans on Extrasolar Planets Using the Glint Effect
• Impact of Clouds and Hazes on the Simulated JWST Transmission Spectra of Habitable Zone Planets in the TRAPPIST-1 System
• The Response of Atmospheric Chemistry on Earthlike Planets around F, G and K Stars to Small Variations in Orbital Distance
• Detectability of atmospheric features of Earth-like planets in the habitable zone around M dwarfs
• On detecting biospheres from chemical thermodynamic disequilibrium in planetary atmospheres
• Detection of Ocean Glint and Ozone Absorption Using LCROSS Earth Observations
• Colors of a Second Earth: Estimating the fractional areas of ocean, land, and vegetation of Earth-like exoplanets
• The First Habitable Zone Earth-sized Planet from TESS. I: Validation of the TOI-700 System
• False negatives for remote life detection on ocean-bearing planets: Lessons from the early Earth
• Detecting and Constraining N${}_2$ Abundances in Planetary Atmospheres Using Collisional Pairs
• Colors of a Second Earth II: Effects of Clouds on Photometric Characterization of Earth-like Exoplanets
• Sensitivity of Biosignatures on Earth-like Planets orbiting in the Habitable Zone of Cool M-Dwarf Stars to varying Stellar UV Radiation and Surface Biomass Emissions
• Effect of Pressure Broadening on Molecular Absorption Cross Sections in Exoplanetary Atmospheres
• Using Deep Space Climate Observatory Measurements to Study the Earth as An Exoplanet
• Modeling the Infrared Spectrum of the Earth-Moon System: Implications for the Detection and Characterization of Earthlike Extrasolar Planets and their Moonlike Companions
• Atmospheric Seasonality as an Exoplanet Biosignature
• Clouds in the atmospheres of extrasolar planets. II. Thermal emission spectra of Earth-like planets influenced by low and high-level clouds
• Introduction of water-vapor broadening coefficients and their temperature dependence exponents into the HITRAN database, Part I: CO2, N2O, CO, CH4, O2, NH3, and H2S
• Understanding planetary context to enable life detection on exoplanets and test the Copernican principle
• Photometric Variability of the Disk Integrated Infrared Emission of the Earth
• Mid-Infrared Properties of Disk Averaged Observations of Earth with AIRS
• The Detectability and Constraints of Biosignature Gases in the Near & Mid-Infrared from Transit Transmission Spectroscopy
• Atmospheric Dynamics on Terrestrial Planets: The Seasonal Response to changes in Orbital, Rotational and Radiative Timescales
• The peak absorbance wavelength of photosynthetic pigments around other stars from spectral optimization
• How surfaces shape the climate of habitable exoplanets
• Earth as an Exoplanet: I. Time variable thermal emission using spatially resolved MODIS data
• Surface and Temporal Biosignatures
• Moderately High Obliquity Promotes Biospheric Oxygenation
• Fundamental Challenges to Remote Sensing of Exo-Earths

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• Earth as an Exoplanet. III. Using Empirical Thermal Emission Spectra as an Input for Atmospheric Retrieval of an Earth-twin Exoplanet
• Pursuing Truth: Improving Retrievals on Mid-Infrared Exo-Earth Spectra with Physically Motivated Water Abundance Profiles and Cloud Models
• Retrieving the Red Edge on Earth-like Planets with Heterogeneous Clouds and Surfaces
• Spectra of Earth-like exoplanets with different rotation periods