Sporadic Spin-orbit Variations in Compact Multiplanet Systems and Their Influence on Exoplanet Climate

Abstract

Climate modeling has shown that tidally influenced terrestrial exoplanets, particularly those orbiting M-dwarfs, have unique atmospheric dynamics and surface conditions that may enhance their likelihood to host viable habitats. However, sporadic libration and rotation induced by planetary interactions, such as those due to mean motion resonances (MMR) in compact planetary systems, may destabilize attendant exoplanets away from synchronized states (1:1 spin-orbit ratios). Here, we use a three-dimensional N-rigid-body integrator and an intermediately complex general circulation model to simulate the evolving climates of TRAPPIST-1 e and f with different orbital- and spin-evolution pathways. Planet f scenarios perturbed by MMR effects with chaotic spin variations are colder and dryer compared to their synchronized counterparts due to the zonal drift of the substellar point away from open ocean basins of their initial eyeball states. On the other hand, the differences between perturbed and synchronized planet e are minor due to higher instellation, warmer surfaces, and reduced climate hysteresis. This is the first study to incorporate the time-dependent outcomes of direct gravitational N-rigid-body simulations into 3D climate modeling of extrasolar planets, and our results show that planets at the outer edge of the habitable zones in compact multiplanet systems are vulnerable to rapid global glaciations. In the absence of external mechanisms such as orbital forcing or tidal heating, these planets could be trapped in permanent snowball states.

Degenerate Interpretations of O3 Spectral Features in Exoplanet Atmosphere Observations Due to Stellar UV Uncertainties: A 3D Case Study with TRAPPIST-1 e

“…Thus, our results, alongside those from Chen et al (2019), demonstrate that 3D modeling results are sensitive to the choice of the assumed stellar UV spectra for potentially habitable tidally locked exoplanets across early and late M dwarf stars and different rotation periods. Future work should also investigate the influence of orbital perturbations away from a synchronous 1:1 spin-orbit resonance (e.g., Chen et al 2023) on composition.…”

Haze Optical Depth in Exoplanet Atmospheres Varies with Rotation Rate: Implications for Observations

“…At its standard T21 resolution, ExoPlaSim can compute a year of climate in roughly 1 minute of runtime (Paradise & Menou 2017). ExoPlaSim has been used in previous studies of the habitability of Earth-like exoplanets (Checlair et al 2017(Checlair et al , 2019Paradise & Menou 2017;Paradise et al 2019) and is particularly suited for simulations over long timescales (Chen et al 2023) or large, unconstrained parameter spaces (macdonald et al 2022). We refer to Haqq-Misra et al (2022) and Paradise et al (2022) for detailed description of the model and its performance compared to other GCMs.…”

The Coupled Impacts of Atmospheric Composition and Obliquity on the Climate Dynamics of TRAPPIST-1e

“…Planet-planet interactions in compact multiplanet systems can cause chaotic spin variations, which affect climate evolution and stability. Chen et al (2023) use an N-rigid-body simulation to investigate the effects of spin-orbit variations for TRAPPIST-1e and f. They find that these variations drive the planets out of spin synchronization, but the climatic influences are less extreme for closer in planets (i.e., TRAPPIST-1e). Although Ohno & Zhang (2019a) suggests that seasonal effects due to eccentricity are weak for planets in regimes IV and V, where the radiative timescale is longer than an orbital period, it would be interesting to compare their results to less idealized models.…”

“…Planets with an orbital period equal to their rotation period and a nonzero obliquity will be forced out of their tidally locked state and experience seasonal cycles. Previous studies (Dobrovolskis 2009;Wang et al 2016;Rauscher 2017;Chen et al 2023) for nonsynchronously rotating planets around Sun-like stars indicate that increasing the obliquity of a planet can increase the outer edge of the habitable zone. For planets with an obliquity above 54°, polar temperatures are higher, and thus it is more difficult for the planet to be globally frozen (Williams & Pollard 2003;Armstrong et al 2014;Kilic et al 2017).…”