Accretion disk’s magnetic field controlled the composition of the terrestrial planets. (arXiv:2009.04311v1 [astro-ph.EP])

Accretion disk’s magnetic field controlled the composition of the terrestrial planets. (arXiv:2009.04311v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+McDonough_W/0/1/0/all/0/1">William F. McDonough</a> (1,2), <a href="http://arxiv.org/find/astro-ph/1/au:+Yoshizaki_T/0/1/0/all/0/1">Takashi Yoshizaki</a> (2) ((1) University of Maryland, College Park, (2) Tohoku Univeristy)

Chondrites, the building blocks of the terrestrial planets, have mass and
atomic proportions of oxygen, iron, magnesium, and silicon totaling $geq$90%
and variable Mg/Si ($sim$25%), Fe/Si (factor of $geq$2), and Fe/O (factor of
$geq$3). The Earth and terrestrial planets (Mercury, Venus, and Mars) are
differentiated into three layers: a metallic core, a silicate shell (mantle and
crust), and a volatile envelope of gases, ices, and, for the Earth, liquid
water. Each layer has different dominant elements (e.g., increasing Fe content
with depth and increasing oxygen content to the surface). What remains an
unknown is to what degree did physical processes during nebular disk accretion
versus those during post-nebular disk accretion (e.g., impact erosion)
influence these final bulk compositions. Here we predict terrestrial planet
compositions and show that their core mass fractions and uncompressed densities
correlate with their heliocentric distance, and follow a simple model of the
magnetic field strength in the protoplanetary disk. Our model assesses the
distribution of iron in terms of increasing oxidation state, aerodynamics, and
a decreasing magnetic field strength outward from the Sun, leading to
decreasing core size of the terrestrial planets with radial distance. This
distribution would enhance habitability in our solar system, and would be
equally applicable to exo-planetary systems.

Chondrites, the building blocks of the terrestrial planets, have mass and
atomic proportions of oxygen, iron, magnesium, and silicon totaling $geq$90%
and variable Mg/Si ($sim$25%), Fe/Si (factor of $geq$2), and Fe/O (factor of
$geq$3). The Earth and terrestrial planets (Mercury, Venus, and Mars) are
differentiated into three layers: a metallic core, a silicate shell (mantle and
crust), and a volatile envelope of gases, ices, and, for the Earth, liquid
water. Each layer has different dominant elements (e.g., increasing Fe content
with depth and increasing oxygen content to the surface). What remains an
unknown is to what degree did physical processes during nebular disk accretion
versus those during post-nebular disk accretion (e.g., impact erosion)
influence these final bulk compositions. Here we predict terrestrial planet
compositions and show that their core mass fractions and uncompressed densities
correlate with their heliocentric distance, and follow a simple model of the
magnetic field strength in the protoplanetary disk. Our model assesses the
distribution of iron in terms of increasing oxidation state, aerodynamics, and
a decreasing magnetic field strength outward from the Sun, leading to
decreasing core size of the terrestrial planets with radial distance. This
distribution would enhance habitability in our solar system, and would be
equally applicable to exo-planetary systems.

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