Size Matters - Lessons from the Interiors of Earth and Mars

Details Size Matters - Lessons from the Interiors of Earth and Mars Size Matters - Lessons from the Interiors of Earth and Mars

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p14b..02s&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #P14B-02

Physics

1213 Earth'S Interior: Dynamics (1507, 7207, 7208, 8115, 8120), 6296 Extra-Solar Planets, 8124 Earth'S Interior: Composition And State (1212, 7207, 7208, 8105), 8147 Planetary Interiors (5430, 5724, 6024)

Scientific paper

Phase transitions at high pressure change material properties and therefore affect the structure and dynamics of the planetary interior. The pressure for current measurements for mantle transitions is generally limited to that of the Earth's core-mantle boundary (CMB). Therefore, transitions at the pressures expected for the mantles (1-10 Mbar) of super-Earths (1-10M⊕) are not well known. However, some lessons can be learned from comparing mantle transitions in Earth (1M⊕, 1.4 Mbar at CMB) and Mars (0.1M⊕, 0.2 Mbar at CMB). Early Earth and Mars may have had deep magma oceans. Our recent study on silicate glasses, frozen forms of melts, shows a series of structural transitions at Earth's mid-mantle pressures. The compositional sensitivity of these transitions may result in compositional stratification in the Earth's magma ocean. However, pressure in the Mars magma ocean is not sufficiently high for this process to occur. This shows that the internal pressure of the planet is an important factor for the initial structure of its mantle. New types of transitions have recently been discovered at pressures within the Earth's deep mantle but beyond the Mars mantle. Iron in mantle phases undergoes changes in electronic configuration (high-spin to low-spin transition) in Earth's deep mantle, leading to changes in optical properties and element partitioning which are important parameters for heat generation and transport. Finally, perovskite undergoes a structural transition (post-perovskite transition) at pressures related to the Earth's CMB region. This transition involves a different type of structural changes compared with the upper-mantle transitions and is responsible for the significant property changes in the CMB region. These examples demonstrate that completely different types of transitions may occur in deep super-Earths. Theory predicts that the energy of an electron becomes comparable or even higher than the binding energy of the electron in an atom as pressure approaches to 10 Mbar, suggesting fundamental changes in chemical bonding of materials at the super-Earth's CMB. A recent computer simulation (Umemoto et al., 2006) suggested a dissociation of MgSiO3 to MgO+SiO2 and metallization of SiO2 at 10 Mbar. The metallic electrical conductivity at the CMB may affect the nutation of super-Earth.

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