With the growing list of confirmed extrasolar planets, discovering and ultimately characterizing an Earth-twin seems to be just around the corner. But observational and theoretical work studying these planets also tell us that a rocky planet with Earth’s mass and radius may have a fundamentally different rotation rate, eccentricity, and/or obliquity (e.g., Barnes, 2017; Dietrick et al., 2018; He et al., 2020). Even Earth’s own history includes smaller-scale variations in day length (e.g., Williams, 2000) and climatically-significant changes in obliquity and eccentricity that form the Milankovitch cycles (e.g., Imbrie et al., 1992). For departures from generally Earth-like parameters, a number of studies have demonstrated the complex (and often substantial) role that orbital parameters play in driving atmospheric dynamics and climatology (e.g., Dressing et al., 2010; Haqq-Misra et al., 2018; Colose et al., 2019).
Because of the radiative properties of key atmospheric constituents, it is critical that explorations of the chemistry and climate of Earth-like planet atmospheres be addressed simultaneously. Here, we highlight some of the ways that photochemical and aerosol processes respond to not only the direct effects of non-terrestrial orbital forcings, but also to the associated climatological conditions that result from those same forcings. To do so, we employ ROCKE-3D (Way et al., 2017), a 3-D general circulation model that has developed from (and now in parallel with) ModelE2 (a modern Earth GCM; Kelley et al., 2020). This allows us to leverage an extensive history of Earth science validations in building an Earth-like (if not necessarily precisely like Earth) ensemble.
Preliminary tests show that there are potentially detectable differences between scenarios with and without chemical, aerosol, and climate interactions, and that interactively simulating the chemistry exaggerates seasonal signals in the integrated planetary spectrum. Particularly in the context of Earth’s biologically-mediated seasonal composition changes (e.g., Olson et al., 2018), these photochemically-driven seasonality signals make a better understanding of the connections between orbital parameters and atmospheric state an essential step towards reliably interpreting observations of terrestrial exoplanets. They also form a bridge connecting ground truth and the nearer-term goals of characterizing rocky planets around smaller stars, which has been the focus of recent work (e.g., Chen et al., 2020).
Chen, H., Wolf, E.T., Zhan, Z. and Horton, D.E., 2019. Habitability and Spectroscopic Observability of Warm M-dwarf Exoplanets Evaluated with a 3D Chemistry-Climate Model. The Astrophysical Journal, 886(1), p.16.
Colose, C.M., Del Genio, A.D. and Way, M.J., 2019. Enhanced habitability on high obliquity bodies near the outer edge of the habitable zone of Sun-like stars. The Astrophysical Journal, 884(2), p.138.
Dressing, C.D., Spiegel, D.S., Scharf, C.A., Menou, K. and Raymond, S.N., 2010. Habitable climates: the influence of eccentricity. The Astrophysical Journal, 721(2), p.1295.
Haqq-Misra, J., Wolf, E.T., Joshi, M., Zhang, X. and Kopparapu, R.K., 2018. Demarcating circulation regimes of synchronously rotating terrestrial planets within the habitable zone. The Astrophysical Journal, 852(2), p.67.
He, M.Y., Ford, E.B., Ragozzine, D. and Carrera, D., 2020. Architectures of Exoplanetary Systems. III. Eccentricity and Mutual Inclination Distributions of AMD-stable Planetary Systems. The Astronomical Journal, 160(6), p.276.
Imbrie, J., Boyle, E.A., Clemens, S.C., Duffy, A., Howard, W.R., Kukla, G., Kutzbach, J., Martinson, D.G., McIntyre, A., Mix, A.C. and Molfino, B., 1992. On the structure and origin of major glaciation cycles 1. Linear responses to Milankovitch forcing. Paleoceanography, 7(6), pp.701-738.
Kelley, M., Schmidt, G.A., Nazarenko, L.S., Bauer, S.E., Ruedy, R., Russell, G.L., Ackerman, A.S., Aleinov, I., Bauer, M., Bleck, R. and Canuto, V., 2020. GISS‐E2. 1: Configurations and climatology. Journal of Advances in Modeling Earth Systems, 12(8), p.e2019MS002025.
Olson, S.L., Schwieterman, E.W., Reinhard, C.T., Ridgwell, A., Kane, S.R., Meadows, V.S. and Lyons, T.W., 2018. Atmospheric seasonality as an exoplanet biosignature. The Astrophysical Journal Letters, 858(2), p.L14.
Way, M.J., Aleinov, I., Amundsen, D.S., Chandler, M.A., Clune, T.L., Del Genio, A.D., Fujii, Y., Kelley, M., Kiang, N.Y., Sohl, L. and Tsigaridis, K., 2017. Resolving orbital and climate keys of earth and extraterrestrial environments with dynamics (ROCKE-3D) 1.0: a general circulation model for simulating the climates of rocky planets. The Astrophysical Journal Supplement Series, 231(1), p.12.
Williams, G.E., 2000. Geological constraints on the Precambrian history of Earth’s rotation and the Moon’s orbit. Reviews of Geophysics, 38(1), pp.37-59.