Habitable Zones & Global Climate

Tidal Excitation Of The Obliquity Of Earth-like Planets In The Habitable Zone Of M-dwarf Stars

By Keith Cowing
Status Report
July 19, 2023
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Tidal Excitation Of The Obliquity Of Earth-like Planets In The Habitable Zone Of M-dwarf Stars
Variation of dω/dt with ω/n for different values of nτ and four different eccentricities: e = 0.05 (red), e = 0.09 (green), e = 0.12 (blue), and e = 0.16 (orange). We adopt θ = 0, and the Hansen coefficients X −3,2 k (e) are truncated at |k| ≤ 20. — astro-ph.EP

Close-in planets undergo strong tidal interactions with the parent star that modify their spins and orbits. In the two-body problem, the final stage for tidal evolution is the synchronisation of the rotation and orbital periods, and the alignment of the planet spin axis with the normal to the orbit (zero planet obliquity).

The orbital eccentricity is also damped to zero, but over a much longer timescale, that may exceed the lifetime of the system. For non-zero eccentricities, the rotation rate can be trapped in spin-orbit resonances that delay the evolution towards the synchronous state. Here we show that capture in some spin-orbit resonances may also excite the obliquity to high values rather than damp it to zero.

Depending on the system parameters, obliquities of 60 to 80 degrees can be maintained throughout the entire lifetime of the planet. This unexpected behaviour is particularly important for Earth-like planets in the habitable zone of M-dwarf stars, as it may help to sustain temperate environments and thus more favourable conditions for life.

Ema F. S. Valente, Alexandre C. M. Correia

Comments: 12 pages, 9 figures, 2 tables
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2307.08770 [astro-ph.EP] (or arXiv:2307.08770v1 [astro-ph.EP] for this version)
Journal reference: Astronomy and Astrophysics, vol. 665, A130 (2022)
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Submission history
From: Alexandre Correia
[v1] Mon, 17 Jul 2023 18:31:16 UTC (2,924 KB)

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻