[Note: These speculations are out of date. Theory now suggests that young brown dwarfs are hot enough to have clouds of iron and silicates. However, these clouds "rain out" as the brown dwarf cools. Brown dwarfs dim as they cool, but this raining out causes a temporary brightening as obscuring clouds are cleared from the atmosphere. Gliese 229 is a cool brown dwarf and most of its atmosphere should be clear of clouds, leaving it a featureless ball glowing a dull red from internal heat.] There is a gray area where an object is too massive to be considered a planet but not massive enough for nuclear fusion to start, the requirement for classification as a star. These "failed stars" are called brown dwarfs and have been theoretical conjecture for years until several were confirmed in 1995. They represent the "missing link" between planets and stars. Unlike planets, brown dwarfs most likely form the same way stars do, condensing out of an interstellar cloud. Planets on the other hand, form from a disk of gas which surrounds a newly formed star. Brown dwarfs will also have more star-like convection currents in the atmosphere and probably no solid core. But unlike stars, brown dwarfs are too cool for nuclear fusion to start. But brown dwarfs still store enough internal heat from when they first collapsed to glow strongly in the infrared. In the case of Gliese 229, 40 Jupiter masses are squezed into a one Jupiter diameter, so the amount of heat stored from its formation is considerable. Because of the cooler temperatures, compounds like methane can form in the atmosphere much like they do in the atmosphere of Jupiter. This methane, and the sub stellar temperature, was detected in the spectrum of Gliese 229 b, proving that the object was not a star. But Gliese 229 b was too massive and too bright to be a planet either. Thus, in November of 1995, Gliese 229 was confirmed as a brown dwarf. We can now get an idea of what Gliese 229 b might be like. Orbiting 44 AU's from it's cool dim red dwarf sun, the brown dwarf is more distant than Pluto's 30 AU orbit from our own sun. If any moons orbit Gliese 229 b they would be frozen dark worlds. However, Gliese 229 b itself would be an inferno. Extremely dense and heated by vast amounts of internal energy, Gliese 229 b glows brightly in the infrared and glows quite noticably in visible light as well. Due to the faintness and distance of its companion star, the brown dwarf emits far more light than it reflects, so both the day and night sides of Gliese 229 b appear the same, glowing red from internal heat. Gliese 229 b would also have titanic magnetic and radiation belts by planetary standards. Any moons having the misfortune of forming near the brown dwarf would have been torn apart by tidal forces long ago. Surviving moons, if they exist, will probably resemble Pluto or Neptune's moon Triton. As on Triton, some moons may be heated enough by tidal forces for methane or nitrogen gysers to form. So the world of Gliese 229 b is a world of extremes. From the superheated glowing atmosphere of the massive brown dwarf to the dark frozen moons waiting out the centuries in the feeble glow of a far away sun, Gliese 229 b is truely a place of fire and ice.
View a VRML model of the system. Please be patient while the file downloads. For a VRML tour of our galaxy's exoplanets, check out Extrasolar VR.
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Current Planet
Habitability Zone
