Mahesh Herath, Charles-Édouard Boukaré, Nicolas B. Cowan
{"title":"Thermal Evolution of Lava Planets","authors":"Mahesh Herath, Charles-Édouard Boukaré, Nicolas B. Cowan","doi":"arxiv-2409.11459","DOIUrl":null,"url":null,"abstract":"Rocky planets are thought to form with a magma ocean that quickly solidifies.\nThe horizontal and vertical extent of this magma ocean depends on the interior\nthermal evolution of the planet, and possibly exogenous processes such as\nplanet migration. We present a model for simulating the thermal history of\ntidally locked lava planets. We initiate the model with a completely molten\nmantle and evolve it for ten billion years. We adopt a fixed surface\ntemperature of 3000 K for the irradiated day-side, but allow the night-side\ntemperature to evolve along with the underlying layers. We simulate planets of\nradius 1.0$R_{\\oplus}$ and 1.5$R_{\\oplus}$ with different core mass fractions,\nalthough the latter does not significantly impact the thermal evolution. We\nconfirm that the day-side magma ocean on these planets has a depth that depends\non the planetary radius. The night-side, on the other hand, begins\ncrystallizing within a few thousand years and completely solidifies within 800\nmillion years in the absence of substantial tidal heating or day-night heat\ntransport. We show that a magma ocean can be sustained on the night-side of a\nlava planet if at least 20 per cent of absorbed stellar power is transmitted\nfrom the day-side to the night-side via magma currents. Such day-night\ntransport could be sustained if the magma has a viscosity of $10^{-3}$ Pa s,\nwhich is plausible at these temperatures. Alternatively, the night-side could\nremain molten if the mush layer is tidally heated at the rate of $8 \\times\n10^{-4}$ W/kg of mush, which is plausible for orbital eccentricities of $e > 7\n\\times 10^{-3}$. Night-side cooling is a runaway process, however: the magma\nbecomes more viscous and the mush solidifies, reducing both day-night heat\ntransport and tidal heating. Measurements of the night-sides of lava planets\nare therefore a sensitive probe of the thermal history of these planets.","PeriodicalId":501209,"journal":{"name":"arXiv - PHYS - Earth and Planetary Astrophysics","volume":"18 1","pages":""},"PeriodicalIF":0.0000,"publicationDate":"2024-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"arXiv - PHYS - Earth and Planetary Astrophysics","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/arxiv-2409.11459","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
引用次数: 0
Abstract
Rocky planets are thought to form with a magma ocean that quickly solidifies.
The horizontal and vertical extent of this magma ocean depends on the interior
thermal evolution of the planet, and possibly exogenous processes such as
planet migration. We present a model for simulating the thermal history of
tidally locked lava planets. We initiate the model with a completely molten
mantle and evolve it for ten billion years. We adopt a fixed surface
temperature of 3000 K for the irradiated day-side, but allow the night-side
temperature to evolve along with the underlying layers. We simulate planets of
radius 1.0$R_{\oplus}$ and 1.5$R_{\oplus}$ with different core mass fractions,
although the latter does not significantly impact the thermal evolution. We
confirm that the day-side magma ocean on these planets has a depth that depends
on the planetary radius. The night-side, on the other hand, begins
crystallizing within a few thousand years and completely solidifies within 800
million years in the absence of substantial tidal heating or day-night heat
transport. We show that a magma ocean can be sustained on the night-side of a
lava planet if at least 20 per cent of absorbed stellar power is transmitted
from the day-side to the night-side via magma currents. Such day-night
transport could be sustained if the magma has a viscosity of $10^{-3}$ Pa s,
which is plausible at these temperatures. Alternatively, the night-side could
remain molten if the mush layer is tidally heated at the rate of $8 \times
10^{-4}$ W/kg of mush, which is plausible for orbital eccentricities of $e > 7
\times 10^{-3}$. Night-side cooling is a runaway process, however: the magma
becomes more viscous and the mush solidifies, reducing both day-night heat
transport and tidal heating. Measurements of the night-sides of lava planets
are therefore a sensitive probe of the thermal history of these planets.