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The requirement that a planet must orbit outside of its Roche limit gives a lower limit on the planets 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 planets 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 planets 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).
Many exoplanets in close-in orbits are observed to have relatively high eccentricities and large stellar obliquities. We explore the possibility that these result from planet-planet scattering by studying the dynamical outcomes from a large number of
Planets are known to orbit giant stars, yet there is a shortage of planets orbiting within ~0.5 AU (P<100 days). First-ascent giants have not expanded enough to engulf such planets, but tidal forces can bring planets to the surface of the star far be
The characterization of four new transiting extrasolar planets is presented here. KOI-188b and KOI-195b are bloated hot Saturns, with orbital periods of 3.8 and 3.2 days, and masses of 0.25 and 0.34 M_Jup. They are located in the low-mass range of kn
Transit surveys have revealed a significant population of compact multi-planet systems, containing several sub-Neptune-mass planets on close-in, tightly-packed orbits. These systems are thought to have formed through a final phase of giant impacts, w
Stimulated by the discovery of a number of close-in low-density planets, we generalise the Jeans escape parameter taking hydrodynamic and Roche lobe effects into account. We furthermore define $Lambda$ as the value of the Jeans escape parameter calcu