Cannonball Planet

There is a growing number of known exoplanets with very short orbital periods of less than half a day. All of these shortest-period exoplanets are expected to be small Earth-mass planets. Larger planets, especially gas giant planets, are unlikely to survive in such short-period orbits. Effects such as tidally-induced orbital decay and evaporation can rapidly destroy a short period gas giant planet. An Earth-mass rocky planet is less susceptible to these effects and can survive almost indefinitely in a very close-in orbit around its parents star. Even so, there is a minimum distance an Earth-mass rocky planet can be from its parent star before tidal forces from the star disintegrate the planet. This minimum distance is known as the Roche limit and the denser a planet, the closer it can orbit its parent star.KOI 1843.03 is a candidate exoplanet detected by the Kepler space telescope. It is 0.6 times the Earth’s diameter and its orbital period of 4.2 hours is probably the shortest known. The requirement that a planet must orbit outside of its Roche limit provides a lower limit to the mean density of this planet. As a result, the mean density of KOI 1843.03 must be at least ...