  We present a deep near-infrared image of the newly discovered brown dwarf
WISE J085510.83-071442.5 (W0855) using the FourStar imager at Las Campanas
Observatory. Our detection of J3=24.8+0.33 -0.53 (J_MKO=25.0+0.33-0.53) at
2.6sigma -- or equivalently an upper limit of J3 > 23.8 (J_MKO > 24.0) at
5sigma makes W0855 the reddest brown dwarf ever categorized (J_MKO - W2 =
10.984+0.33 - 0.53 at 2.6sigma -- or equivalently an upper limit of J_MKO - W2
> 9.984 at 5sigma) and refines its position on color magnitude diagrams.
Comparing the new photometry with chemical equilibrium model atmosphere
predictions, we demonstrate that W0855 is 4.5sigma from models using a
cloudless atmosphere and well reproduced by partly cloudy models (50%)
containing sulfide and water ice clouds. Non-equilibrium chemistry or non-solar
metallicity may change predictions, however using currently available model
approaches, this is the first candidate outside our own solar system to have
direct evidence for water clouds.
