Neptune-Sized Planet Orbiting a Baby Star

Mann et al. (2016) present the discovery of a super-Neptune-sized planet in a close-in orbit around a low-mass pre-main sequence star. This planet is identified as EPIC 205117205b. Its size is estimated to be ~5 times the diameter of Earth and it orbits its host star every 5.425 days. The host star of EPIC 205117205b is estimated to have 0.54 times the mass, 1.06 times the radius and 0.17 times the luminosity of the Sun. Notice that the radius and luminosity are both way too large for a star of this mass. This is because the host star of EPIC 205117205b is still in the process of contracting and settling down as a red dwarf star. Its age is estimated to be less than ~11 million years. The discovery of EPIC 205117205b suggests that close-in planets can form where they already are, or they can form further out and then migrate rapidly, within ~10 million years, to their present close-in orbits.

Reference:
Mann et al. (2016), "Zodiacal Exoplanets in Time (ZEIT) III: A Neptune-sized planet orbiting a pre-main-sequence star in the Upper Scorpius OB Association", arXiv:1604.06165 [astro-ph.EP]