Variation due to climate and chemistry in Earth analogue oxygenated exoplanet observations

This figure shows how the seasons can affect the spectra of the exoplanets. In Jy units, the total flux received by the telescope (𝐹𝑇 = 𝐹𝑝 + 𝐹 βˆ—) in the radial direction versus phase in the azimuthal direction is plotted. This is for 48 hours of integration using LUVOIR A for an exoplanet on 10 PCs. A standard year is plotted, then the observer’s geometry is rotated +90Β°, +180Β°, +270Β°. ‘yr 2’ and ‘yr 3’ refer to the second and third years of the last four-year data set, respectively. Top: Contrast is shown in pre-industrial atmospheres, 0.1% PAL for oxygen at 0.76 Β΅M and H2O at 0.94 Β΅M. The width of the lines represents the uncertainty in noise Β±1 for the observations. Bottom: The broadband contrast of the UV and VIS channels with phase is shown. The discontinuity is in the curves between December 27 and January 1. The shaded areas in purple represent exoplanet phases within the inner working angle (IWA) in LUVOIR A. Line width represents wide-band uncertainty Β±1-𝜎

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The Great Oxidation Event was a period in which concentrations of Earth’s atmospheric oxygen (O2) increased from 10βˆ’5 times the current atmospheric level (PAL) to nearly modern levels, marking the beginning of the primitive geological age 2.4 billion years ago.

Using WACCM6, the Earth System Model, we simulate the atmosphere of Earth’s analogue exoplanets with O2 mixing ratios between 0.1% and 150% PAL. Using this simulation, we calculate the reflection/emission spectra across multiple orbits using a planetary spectrum generator.

We highlight how observer angle, albedo, chemistry, and clouds affect simulated observations. We show that interannual climatic changes, as well as short-term changes due to clouds, can be observed in our simulated atmospheres with a telescope concept such as LUVOIR or HabEx.

Annual variability and seasonal variation can alter a planet’s reflected flux (including the reflective flux of key spectral features such as O2 and H2O) by up to factors of 5 and 20, respectively, for the same orbital phase.

This contrast can be best observed with a high-throughput coronal vertebra. For example, the stellar shadow HabEx (4 m) performs twice as well as the LUVOIR B telescope (6 m). The contrast and signal-to-noise ratio of some spectral features depend nonlinearly on the oxygen concentration in the atmosphere.

This is caused by changes in temperature and chemical column depth, as well as increased liquid content and ice clouds in general for atmospheres with O2 concentrations <1% PAL.

Gregory Cook (1), Dan Marsh (1 and 2), Catherine Walsh (1), Sarah Rogaimer (3 and 4), Jeronimo Villanueva (5) ((1) School of Physics and Astronomy, University of Leeds, UK, (2) National Center for Atmospheric Research, Boulder, USA, (3) University of Oxford, Department of Atmospheric, Oceanic and Planetary Physics, UK, (4) Department of Physics and Astronomy, York University, Canada, (5) NASA Goddard Space Flight Center, Department of Solar System Exploration, USA)

Comments: 14 pages, 7 numbers. Accepted for publication in MNRAS
Topics: Earth and Planetary Astrophysics (astro-ph.EP)
Cited as follows: arXiv: 2209.07566 [astro-ph.EP] (or arXiv: 2209.07566v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2209.07566
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WHO: Gregory Cook
[v1] Thursday, September 15, 2022 19:10:00 UTC (9,395 KB)
https://arxiv.org/abs/2209.07566
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