A planet within the debris disk around the pre-main sequence star AU Mic

AU Microscopii (AU Mic) is the second closest (d = 9.79 parsec) pre-main sequence (22 Myr) star. AU Mic possesses a relatively rare and spatially resolved edge-on debris disk extending from ~35–210 astronomical units from the star, and with clumps exhibiting non-Keplerian motion . Detection of newly-formed planets around such a star is challenged by the presence of spots, plage, flares and other manifestations of magnetic “activity” on the star. Here we report the discovery of a planet transiting AU Mic. The transiting planet, AU Mic b, has an orbital period of 8.47 days, an orbital distance of 0.06 astronomical units, a radius of 0.4 Jupiter radii, and a mass less than 0.18 Jupiter masses at 3-σ confidence. This very young, nearby planet represents an unparalleled opportunity to study its atmosphere and its interaction with the host star at a very early stage in its evolution.