Lava Planets Interior Dynamics Govern The Long-term Evolution Of Their Magma Oceans

By Keith Cowing
Status Report
August 31, 2023
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Lava Planets Interior Dynamics Govern The Long-term Evolution Of Their Magma Oceans
Compositional evolution of lava planets interiors from an initial homogeneous molten state. Chemical fractionation occurs during planetary solidification because rock-forming elements do not have the same affinities for liquid and solid phases. For instance, FeO prefers to remain in the liquid rather than being incorporated in the solids. (a and b) Initial conditions. The magma ocean is well mixed and nearly entirely molten. The composition of the magma ocean corresponds to the bulk planet’s composition, i.e., 6% of FeO (BSE composition). This is the global magma ocean stage. (c and d) Onset of the mushy stage. The MO crystal fraction is about 50%. Iron-rich solids accumulate in the deep mantle. The most liquid part of the planet shows a FeO content of 10%. (e-f) End of the mushy stage. The FeO concentration of the MO reaches its maximum, 12%. (g-h) Solid-state stage. The iron-rich shallow magma ocean has been buried in the deep mantle. The day-side shallow magma ocean has a concentration of about about 2%. The solid mantle is strongly layered. Iron-rich solids remelts to form a basal magma ocean. — astro-ph.EP]

Lava planets are rocky exoplanets that orbit so close to their host star that their day-side is hot enough to melt silicate rock. Their short orbital periods ensure that lava planets are tidally locked into synchronous rotation, with permanent day and night hemispheres. Such asymmetric magma oceans have no analogs in the Solar System and will exhibit novel fluid dynamics.

Here we report numerical simulations of lava planet interiors showing that solid-liquid fractionation in the planetary interior has a major impact on the compositional structure and evolution of the planet. We explored two styles of dynamics that depend primarily on the interior thermal state : 1) a hot fully molten interior, and 2) a mostly solid interior with a shallow day-side magma ocean.

In the hot interior scenario, the atmosphere reflects the planet’s bulk silicate composition and the night-side crust is gravitationally unstable and constantly replenished. In the cool interior scenario, the distilled atmosphere will lack Na, K and FeO, and the night-side mantle is entirely solid, with a cold surface. These two end-member cases can be distinguished with observations from the James Webb Space Telescope, offering an avenue to probe the diversity of terrestrial exoplanet evolutions.

Charles-Édouard Boukaré, Daphné Lemasquerier, Nicolas Cowan, Henri Samuel, James Badro

Comments: 12 pages, 4 figures. Supplementary informations are included
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Fluid Dynamics (physics.flu-dyn); Geophysics (physics.geo-ph)
Cite as: arXiv:2308.13614 [astro-ph.EP] (or arXiv:2308.13614v1 [astro-ph.EP] for this version)
Submission history
From: Charles-Édouard Boukaré
[v1] Fri, 25 Aug 2023 18:15:14 UTC (11,138 KB)
Astrobiology, Astrogeology,

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) 🖖🏻