¹John H.D.Harrison,^1,2Oliver Shorttle,¹Amy Bonsor
Earth and Planetary Science Letters 554, 116694 Link to Article [https://doi.org/10.1016/j.epsl.2020.116694]
¹Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, UK
²Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, UK
Copyright Elsevier

The loss and gain of volatile elements during planet formation is key for setting their subsequent climate, geodynamics, and habitability. Two broad regimes of volatile element transport in and out of planetary building blocks have been identified: that occurring when the nebula is still present, and that occurring after it has dissipated. Evidence for volatile element loss in planetary bodies after the dissipation of the solar nebula is found in the high Mn to Na abundance ratio of Mars, the Moon, and many of the solar system’s minor bodies. This volatile loss is expected to occur when the bodies are heated by planetary collisions and short-lived radionuclides, and enter a global magma ocean stage early in their history. The bulk composition of exo-planetary bodies can be determined by observing white dwarfs which have accreted planetary material. The abundances of Na, Mn, and Mg have been measured for the accreting material in four polluted white dwarf systems. Whilst the Mn/Na abundances of three white dwarf systems are consistent with the fractionations expected during nebula condensation, the high Mn/Na abundance ratio of GD362 means that it is not (). We find that heating of the planetary system orbiting GD362 during the star’s giant branch evolution is insufficient to produce such a high Mn/Na. We, therefore, propose that volatile loss occurred in a manner analogous to that of the solar system bodies, either due to impacts shortly after their formation or from heating by short-lived radionuclides. We present potential evidence for a magma ocean stage on the exo-planetary body which currently pollutes the atmosphere of GD362.

¹K. Righter,²R. Rowland II,²L. R. Danielson,³M. Humayun,³S. Yang,
⁴N. Mayer (Waeselmann),⁵K. Pando
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13598]
¹NASA Johnson Space Center, Mailcode XI2, 2101 NASA Parkway, Houston, Texas, 77058 USA
²Los Alamos National Laboratory, Mail Stop P952, Los Alamos, New Mexico, 87545 USA
³National High Magnetic Field Laboratory, and Department of Earth, Ocean & Atmospheric Science, Florida State University, Tallahassee, Florida, 32310 USA
⁴Mineralogisch‐Petrographisches Institut (MPI), University of Hamburg, Grindelallee, 48, 20146 Hamburg, Germany
⁵Jacobs JETS, 2101 NASA Parkway, NASA Johnson Space Center, Houston, Texas, 77058 USA
Published by arrangement with John Wiley & Sons

Trace elements and extant and extinct isotopic attributes in Martian meteorites have been used to argue that Mars accreted quickly, differentiated into core and mantle, and established several mantle reservoirs, possibly within 10 Ma of T0. The partitioning of trace elements in the deep mantle has been relatively unstudied, despite the need for such knowledge in understanding magma ocean crystallization and the origin of depleted and enriched mantle reservoirs. The siderophile element composition of the Martian mantle and lithophile isotopic systems such as Sr, Hf, and Nd are thought to record evidence for early metal–silicate equilibrium and deep magma ocean at an intermediate depth and pressure of 800 km or 14 GPa. We have carried out experiments across this pressure range to better understand the mineral/melt partitioning of a wide range of elements. These new data are used to evaluate differentiation models for Mars and to help interpret the available isotopic data. The relatively incompatible nature of Re compared to mildly compatible Os means that the crystallization of a deep magma ocean will lead to residual liquids with superchondritic Re/Os, and solids with subchondritic Re/Os. Such material available in the mantle could be the source of enriched isotopic reservoir that produced shergottites with +γOs values. Slightly subchondritic Re/Os ratios in the crystallizing solids would provide a reservoir that could produce −γOs values. Melting of mixtures of these two enriched and depleted endmembers could explain the Nd‐Os isotopic correlations and systematics of shergottites.