We present the discovery of a young L dwarf , WISE J231921.92+764544.4 , identified by comparing the Wide-field Infrared Survey Explorer ( WISE ) All-Sky Catalog to the Two Micron All Sky Survey ( 2MASS ) .
A medium-resolution optical spectrum provides a spectral type of L4 \beta , with a photometric distance estimate of 26.1 \pm 4.4 pc .
The red WISE W 1 - W 2 color provides additional evidence of youth , while the 2MASS J - K _ { s } color does not .
WISE J231921.92+764544.4 is a candidate member of the young moving group Argus , with the space motion and position of WISE J231921.92+764544.4 giving a probability of 79 % membership in Argus and a probability of 21 % as a field object , based on BANYAN II .
WISE J231921.92+764544.4 has a mass of 12.1 \pm 0.4 M _ { Jup } based on membership in Argus , within the planetary mass regime .