Kavli Affiliate: Alan Levine

| First 5 Authors: Saul Rappaport, Roberto Sanchis-Ojeda, Leslie A. Rogers, Alan Levine, Joshua N. Winn

| Summary:

The requirement that a planet must orbit outside of its Roche limit gives a

lower limit on the planet’s mean density. The minimum density depends almost

entirely on the orbital period and is immune to systematic errors in the

stellar properties. We consider the implications of this density constraint for

the newly-identified class of small planets with periods shorter than half a

day. When the planet’s radius is known accurately, this lower limit to the

density can be used to restrict the possible combinations of iron and rock

within the planet. Applied to KOI 1843.03, with a radius of 0.6 Earth radii and

the shortest known orbital period of 4.245 hr, the planet’s mean density must

be greater than approximately 7 g/cm^3. By modeling the planetary interior

subject to this constraint, we find the composition of the planet must be

mostly iron, with at most a modest fraction of silicates (less than

approximately 30% by mass).

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