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Title: THERMODYNAMIC LIMITS ON MAGNETODYNAMOS IN ROCKY EXOPLANETS

Abstract

To ascertain whether magnetic dynamos operate in rocky exoplanets more massive or hotter than the Earth, we developed a parametric model of a differentiated rocky planet and its thermal evolution. Our model reproduces the established properties of Earth's interior and magnetic field at the present time. When applied to Venus, assuming that planet lacks plate tectonics and has a dehydrated mantle with an elevated viscosity, the model shows that the dynamo shuts down or never operated. Our model predicts that at a fixed planet mass, dynamo history is sensitive to core size, but not to the initial inventory of long-lived, heat-producing radionuclides. It predicts that rocky planets larger than 2.5 Earth masses will not develop inner cores because the temperature-pressure slope of the iron solidus becomes flatter than that of the core adiabat. Instead, iron 'snow' will condense near or at the top of these cores, and the net transfer of latent heat upward will suppress convection and a dynamo. More massive planets can have anemic dynamos due to core cooling, but only if they have mobile lids (plate tectonics). The lifetime of these dynamos is shorter with increasing planet mass but longer with higher surface temperature. Massive Venus-like planetsmore » with stagnant lids and more viscous mantles will lack dynamos altogether. We identify two alternative sources of magnetic fields on rocky planets: eddy currents induced in the hot or molten upper layers of planets on very short-period orbits, and dynamos in the ionic conducting layers of 'ocean' planets with {approx}10% mass in an upper mantle of water (ice).« less

Authors:
;  [1]; ;  [2]
  1. Department of Geology and Geophysics, University of Hawaii at Manoa, Honolulu, HI 96822 (United States)
  2. Department of Earth and Planetary Science, University of California at Berkeley, Berkeley, CA 94720 (United States)
Publication Date:
OSTI Identifier:
21455117
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 718; Journal Issue: 2; Other Information: DOI: 10.1088/0004-637X/718/2/596; Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; EDDY CURRENTS; ICE; IRON; MAGNETIC FIELDS; SATELLITES; SOLAR SYSTEM EVOLUTION; VENUS PLANET; CURRENTS; ELECTRIC CURRENTS; ELEMENTS; EVOLUTION; METALS; PLANETS; TRANSITION ELEMENTS

Citation Formats

Gaidos, Eric, Conrad, Clinton P, Manga, Michael, and Hernlund, John. THERMODYNAMIC LIMITS ON MAGNETODYNAMOS IN ROCKY EXOPLANETS. United States: N. p., 2010. Web. doi:10.1088/0004-637X/718/2/596.
Gaidos, Eric, Conrad, Clinton P, Manga, Michael, & Hernlund, John. THERMODYNAMIC LIMITS ON MAGNETODYNAMOS IN ROCKY EXOPLANETS. United States. doi:10.1088/0004-637X/718/2/596.
Gaidos, Eric, Conrad, Clinton P, Manga, Michael, and Hernlund, John. Sun . "THERMODYNAMIC LIMITS ON MAGNETODYNAMOS IN ROCKY EXOPLANETS". United States. doi:10.1088/0004-637X/718/2/596.
@article{osti_21455117,
title = {THERMODYNAMIC LIMITS ON MAGNETODYNAMOS IN ROCKY EXOPLANETS},
author = {Gaidos, Eric and Conrad, Clinton P and Manga, Michael and Hernlund, John},
abstractNote = {To ascertain whether magnetic dynamos operate in rocky exoplanets more massive or hotter than the Earth, we developed a parametric model of a differentiated rocky planet and its thermal evolution. Our model reproduces the established properties of Earth's interior and magnetic field at the present time. When applied to Venus, assuming that planet lacks plate tectonics and has a dehydrated mantle with an elevated viscosity, the model shows that the dynamo shuts down or never operated. Our model predicts that at a fixed planet mass, dynamo history is sensitive to core size, but not to the initial inventory of long-lived, heat-producing radionuclides. It predicts that rocky planets larger than 2.5 Earth masses will not develop inner cores because the temperature-pressure slope of the iron solidus becomes flatter than that of the core adiabat. Instead, iron 'snow' will condense near or at the top of these cores, and the net transfer of latent heat upward will suppress convection and a dynamo. More massive planets can have anemic dynamos due to core cooling, but only if they have mobile lids (plate tectonics). The lifetime of these dynamos is shorter with increasing planet mass but longer with higher surface temperature. Massive Venus-like planets with stagnant lids and more viscous mantles will lack dynamos altogether. We identify two alternative sources of magnetic fields on rocky planets: eddy currents induced in the hot or molten upper layers of planets on very short-period orbits, and dynamos in the ionic conducting layers of 'ocean' planets with {approx}10% mass in an upper mantle of water (ice).},
doi = {10.1088/0004-637X/718/2/596},
journal = {Astrophysical Journal},
issn = {0004-637X},
number = 2,
volume = 718,
place = {United States},
year = {2010},
month = {8}
}