  We present Gemini near-infrared adaptive optics imaging and spectroscopy of a
planetary mass candidate companion to 1RXS J160929.1-210524, a roughly
solar-mass member of the 5 Myr-old Upper Scorpius association. The object,
separated by 2.22" or 330 AU at ~150 pc, has infrared colors and spectra
suggesting a temperature of 1800(-100/+200) K, and spectral type of L4(-2/+1).
The H- and K-band spectra provide clear evidence of low surface gravity, and
thus youth. Based on the widely used DUSTY models, we infer a mass of
8(-2/+4)Mjupiter. If gravitationally bound, this would be the lowest mass
companion imaged around a normal star thus far, and its existence at such a
large separation would pose a serious challenge to theories of star and planet
formation.
