Variability Due To Climate And Chemistry In Observations Of Oxygenated Earth-analogue Exoplanets

Variability due to climate and chemistry in observations of oxygen-rich Earth-analogous exoplanets

This figure shows how seasons can affect the spectra of exoplanets. In units of Jy, the total flux received by the telescope (𝐹𝑇 = 𝐹𝑝 + 𝐹∗) in the radial direction is plotted against the phase in the azimuthal direction. This is for a 48 hour integration time using LUVOIR A for an exoplanet at 10 pc. A standard year is drawn, and then the observer geometry is rotated by +90◦ , +180◦ , and +270◦ . “2. year” and “3. Year” refer to the 2nd and 3rd year of the final 4-year dataset. Above: Deviations for the pre-industrial and 0.1% PAL atmosphere are shown for O2 at 0.76 µm and H2O at 0.94 µm. The width of the lines represents the ±1-𝜎noise uncertainty of the observations. Below: The broadband course is shown in the UV and VIS channel with phase. The discontinuity in the curves is between December 27th and January 1st. The magenta areas represent phases where the exoplanet would be within the inner working angle (IWA) of the LUVOIR A coronagraph. The width of the lines represents the ±1-𝜎noise broadband uncertainty


The Great Oxidation Event was a period in which the concentration of the Earth’s atmospheric oxygen (O2) increased from 10 to 5 times the current atmospheric level (PAL) to nearly present levels, marking the beginning of the Proterozoic geological eon 2 .4 billion years ago.

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Using WACCM6, an Earth system model, we simulate the atmosphere of Earth-analogous exoplanets with O2 mixing ratios between 0.1% and 150% PAL. With these simulations we calculate the reflection/emission spectra over several orbits with the Planetary Spectrum Generator.

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

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Annual and seasonal variations can alter the planet’s reflected flux (including the reflected 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 variability is best observed with a high throughput coronagraph. For example, HabEx (4m) with a star umbrella is up to 2x better than a LUVOIR B (6m) telescope. The variability and signal-to-noise ratio of some spectral features depend non-linearly on the atmospheric O2 concentration.

This is caused by variations in chemical column temperature and depth, and generally increased liquid and ice cloud content for atmospheres with O2 concentrations <1% PAL.

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

Commentary: 14 pages, 7 illustrations. Accepted for publication in MNRAS
Subjects: Astrophysics of the Earth and Planets (astro-ph.EP)
Cite as: arXiv:2209.07566 [astro-ph.EP] (or arXiv:2209.07566v1 [astro-ph.EP] for this version)
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Submission History
By: Gregory Cooke
[v1] Thu, September 15, 2022 19:10:00 UTC (9,395 KB)

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