Kepler-407b is a transiting Earth-size planet detected by NASA’s Kepler space telescope. Measuring 1.07 ± 0.02 times the radius of Earth, Kepler-407b also whizzes around its host star, a Sun-like star, in an extremely close-in orbit with a period of only 16 hours. At such close proximity to its host star, temperatures on the planet’s day side are expected to reach well over 2000 K.
Kepler-407b is most likely tidally-locked with the same side of the planet always pointed towards its host star. A lave ocean could exist on the planet’s intensely hot day side where temperatures are too high for rock material to remain solid. Kepler-407b joins a growing list of planets with orbital periods less than 24 hours. Other similar planets include Kepler-10b and Kepler-78b.
Follow-up radial velocity (RV) measurements to determine the mass of Kepler-407b could only provide a one sigma upper limit of 1.7 times the mass of Earth. These RV measurements also detected the partial orbit of an outer, non-transiting planet, hereafter identified as Kepler-407c. Given that only a quarter of a potentially ~10 year long orbit was measured by RV, the planet’s orbit and mass could only be weakly constrained.
Kepler-407c is estimated to have an orbital period of 3000 ± 500 days and somewhere between 5 to 20 times the mass of Jupiter. However, depending on the inclination of its orbit, Kepler-407c could also be a more massive object such as a brown dwarf or even a red dwarf star. Future RV measurements will be needed to better constrain the masses of both Kepler-407b and c.
Marcy et al. (2014), “Masses, Radii, and Orbits of Small Kepler Planets: The Transition from Gaseous to Rocky Planets”, arXiv:1401.4195 [astro-ph.EP]