A new class of Super-Earths formed from high-temperature condensates: HD219134 b, 55 Cnc e, WASP-47 e. (arXiv:1812.07222v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Dorn_C/0/1/0/all/0/1">Caroline Dorn</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Harrison_J/0/1/0/all/0/1">John H. D. Harrison</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bonsor_A/0/1/0/all/0/1">Amy Bonsor</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hands_T/0/1/0/all/0/1">Tom O. Hands</a>
We hypothesise that differences in the temperatures at which the rocky
material condensed out of the nebula gas can lead to differences in the
composition of key rocky species (e.g., Fe, Mg, Si, Ca, Al, Na) and thus planet
bulk density. Such differences in the observed bulk density of planets may
occur as a function of radial location and time of planet formation. In this
work we show that the predicted differences are on the cusp of being detectable
with current instrumentation. In fact, for HD 219134, the 10 % lower bulk
density of planet b compared to planet c could be explained by enhancements in
Ca, Al rich minerals. However, we also show that the 11 % uncertainties on the
individual bulk densities are not sufficiently accurate to exclude the absence
of a density difference as well as differences in volatile layers. Besides HD
219134 b, we demonstrate that 55 Cnc e and WASP-47 e are similar candidates of
a new Super-Earth class that have no core and are rich in Ca and Al minerals
which are among the first solids that condense from a cooling proto-planetary
disc. Planets of this class have densities 10-20% lower than Earth-like
compositions and may have very different interior dynamics, outgassing
histories and magnetic fields compared to the majority of Super-Earths.
We hypothesise that differences in the temperatures at which the rocky
material condensed out of the nebula gas can lead to differences in the
composition of key rocky species (e.g., Fe, Mg, Si, Ca, Al, Na) and thus planet
bulk density. Such differences in the observed bulk density of planets may
occur as a function of radial location and time of planet formation. In this
work we show that the predicted differences are on the cusp of being detectable
with current instrumentation. In fact, for HD 219134, the 10 % lower bulk
density of planet b compared to planet c could be explained by enhancements in
Ca, Al rich minerals. However, we also show that the 11 % uncertainties on the
individual bulk densities are not sufficiently accurate to exclude the absence
of a density difference as well as differences in volatile layers. Besides HD
219134 b, we demonstrate that 55 Cnc e and WASP-47 e are similar candidates of
a new Super-Earth class that have no core and are rich in Ca and Al minerals
which are among the first solids that condense from a cooling proto-planetary
disc. Planets of this class have densities 10-20% lower than Earth-like
compositions and may have very different interior dynamics, outgassing
histories and magnetic fields compared to the majority of Super-Earths.
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