System 91
Star system 91
This system consists of a brown dwarf and red dwarf orbiting a yellow G dwarf.  With a surface temperature of only 444 K, the brown
dwarf is especially interesting. Brown dwarfs are sometimes cooler than this, but most are warmer and this one is particularly methane
rich. This is a cool T type brown dwarf. Molecules such as methane only form in the cooler outer layers of cool k, M and brown dwarf
stars. Here the methane is abundant and the photosphere is dominated by rotary motion rather than by convection, as it can be in
hotter and also younger brown dwarfs. This gives the atmosphere some characteristics of a gas giant planetary atmosphere, though its
is appreciably warmer and more luminous. Cloud bands of methane dust and other molecules can be seen.
Cool methane rich brown dwarf