Exoplanets & Exomoons

Super-Earth LHS3844b Is Tidally Locked

By Keith Cowing
Status Report
October 4, 2023
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Super-Earth LHS3844b Is Tidally Locked
Effect of space weathering on the single scattering albedo of basalt (left column), and resulting thermal phase curves (right column). Top row shows the effect of space weathering via the formation of nanophase metallic iron particles (npFe), bottom row shows the effect of space weathering via graphite. Percentages show the added volume fraction of darkening material. — astro-ph.EP

Short period exoplanets on circular orbits are thought to be tidally locked into synchronous rotation. If tidally locked, these planets must possess permanent day- and nightsides, with extreme irradiation on the dayside and none on the nightside. However, so far the tidal locking hypothesis for exoplanets is supported by little to no empirical evidence.

Previous work showed that the super-Earth LHS 3844b likely has no atmosphere, which makes it ideal for constraining the planet’s rotation. Here we revisit the Spitzer phase curve of LHS 3844b with a thermal model of an atmosphere-less planet and analyze the impact of non-synchronous rotation, eccentricity, tidal dissipation, and surface composition. Based on the lack of observed strong tidal heating we rule out rapid non-synchronous rotation (including a Mercury-like 3:2 spin-orbit resonance) and constrain the planet’s eccentricity to less than 0.001 (more circular than Io’s orbit).

In addition, LHS 3844b’s phase curve implies that the planet either still experiences weak tidal heating via a small-but-nonzero eccentricity (requiring an undetected orbital companion), or that its surface has been darkened by space weathering; of these two scenarios we consider space weathering more likely. Our results thus support the hypothesis that short period rocky exoplanets are tidally locked, and further show that space weathering can significantly modify the surfaces of atmosphere-less exoplanets.

Xintong Lyu, Daniel D.B. Koll, Nicolas B. Cowan, Renyu Hu, Laura Kreidberg, Brain E.J. Rose

Comments: Submitted
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2310.01725 [astro-ph.EP] (or arXiv:2310.01725v1 [astro-ph.EP] for this version)
Submission history
From: Xintong Lyu
[v1] Tue, 3 Oct 2023 01:22:13 UTC (1,589 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) 🖖🏻