Tidally-Distorted, Iron-Enhanced Exoplanets Closely Orbiting Their Stars. (arXiv:1901.10666v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Price_E/0/1/0/all/0/1">Ellen M. Price</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Rogers_L/0/1/0/all/0/1">Leslie A. Rogers</a>

The origin of Mercury’s enhanced iron content is a matter of ongoing debate.
The characterization of rocky exoplanets promises to provide new, independent
insights on this topic by constraining the occurrence rate and physical and
orbital properties of iron-enhanced planets orbiting distant stars. The
transiting planet candidate KOI 1843.03 (0.6 Earth radius, 4.245 hour orbital
period, 0.46 solar mass host star) has the shortest orbital period of any
planet yet discovered. Here we show, using the first three-dimensional interior
structure simulations of ultra-short-period tidally distorted rocky exoplanets,
that KOI 1843.03 may be shaped like an American football, elongated along the
planet-star axis with an aspect ratio of up to 1.79. Furthermore, for KOI
1843.03 to have avoided tidal disruption (wherein the planet is pulled apart by
the tidal gravity of its host star) on such a close-in orbit, KOI 1843.03 must
be as iron-rich as Mercury (about 66% by mass iron compared to Mercury’s 70% by
mass iron). Of the ultra-short-period (P < 1 day) planets with physically-meaningful constraints on their densities characterized to date, just under half (4 out of 9) are iron-enhanced. As more are discovered, we will better understand the origin of the planet Mercury in our Solar System.

The origin of Mercury’s enhanced iron content is a matter of ongoing debate.
The characterization of rocky exoplanets promises to provide new, independent
insights on this topic by constraining the occurrence rate and physical and
orbital properties of iron-enhanced planets orbiting distant stars. The
transiting planet candidate KOI 1843.03 (0.6 Earth radius, 4.245 hour orbital
period, 0.46 solar mass host star) has the shortest orbital period of any
planet yet discovered. Here we show, using the first three-dimensional interior
structure simulations of ultra-short-period tidally distorted rocky exoplanets,
that KOI 1843.03 may be shaped like an American football, elongated along the
planet-star axis with an aspect ratio of up to 1.79. Furthermore, for KOI
1843.03 to have avoided tidal disruption (wherein the planet is pulled apart by
the tidal gravity of its host star) on such a close-in orbit, KOI 1843.03 must
be as iron-rich as Mercury (about 66% by mass iron compared to Mercury’s 70% by
mass iron). Of the ultra-short-period (P < 1 day) planets with
physically-meaningful constraints on their densities characterized to date,
just under half (4 out of 9) are iron-enhanced. As more are discovered, we will
better understand the origin of the planet Mercury in our Solar System.

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