Observations of accretion disks around young brown dwarfs have led to the speculation that they may form planetary systems similar to normal stars .
While there have been several detections of planetary-mass objects around brown dwarfs ( 2MASS 1207-3932 and 2MASS 0441-2301 ) , these companions have relatively large mass ratios and projected separations , suggesting that they formed in a manner analogous to stellar binaries .
We present the discovery of a planetary-mass object orbiting a field brown dwarf via g ravitational microlensing , OGLE-2012-BLG-0358Lb .
The system is a low secondary/primary mass ratio ( 0.080 \pm 0.001 ) , relatively tightly-separated ( \sim 0.87 AU ) binary composed of a planetary-mass object with 1.9 \pm 0.2 Jupiter masses orbiting a brown dwarf with a mass 0.022 M _ { \odot } .
The relatively small mass ratio and separation suggest that the companion may have formed in a protoplanetary disk around the brown dwarf host , in a manner analogous to planets .