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We have used Pan-STARRS1 to discover an extremely red late-L dwarf, which has(J-K)_MKO = 2.84 and (J-K)_2MASS = 2.78, making it the reddest known fielddwarf and second only to 2MASS J1207-39b among substellar companions. Near-IRspectroscopy shows a spectral type of L7 and reveals a triangular H-bandcontinuum and weak alkali (K I and Na I) lines, hallmarks of low surfacegravity. Near-IR astrometry from the Hawaii Infrared Parallax Program gives adistance of 24.6+/-1.4 pc and indicates a much fainter J-band absolutemagnitude than field L dwarfs. The position and kinematics of PSO J318-22 pointto membership in the beta Pictoris moving group. Evolutionary models give atemperature of 1160 (-40,+30) K and a mass of 6.5 (-1.0, +1.3) Mjup, making PSOJ318-22 one of the lowest mass free-floating objects in the solar neighborhood.This object adds to the growing list of low-gravity field L dwarfs and is thefirst to be strongly deficient in methane relative to its estimatedtemperature. Comparing their spectra suggests that young L dwarfs with similarages and temperatures can have different spectral signatures of youth. For thetwo objects with well constrained ages (PSO J318-22 and 2MASS J0355+11), wefind their temperatures are ~400 K cooler than field objects of similarspectral type but their luminosities are comparable, i.e., these young L dwarfsare very red and unusually cool but not "underluminous." Altogether, PSOJ318-22 is the first free-floating object with the colors, magnitudes,spectrum, luminosity, and mass that overlap the young dusty planets around HR8799 and 2MASS J1207-39.

The Extremely Red, Young L Dwarf PSO J318-22: A Free-Floating Planetary-Mass Analog to Directly Imaged Young Gas-Giant Planets