Jupiter's Cool New Belt
Thanks to last summer's comet impacts, Jupiter sports a new dark belt in its southern hemisphere, the second-most obvious one on the planet after the South Equatorial Belt. Astronomers using the 3.5-meter reflector on Calar Alto report that a continuous bright band can be seen in that latitude range at the infrared wavelength of 1.7 microns. This means that debris ejected upward remains suspended high in the atmosphere. Now a team of European astronomers report that the band is significantly dimmer -- and thus cooler -- than its surroundings in the thermal infrared at 7.8 and 7.9 microns. These wavelengths are sensitive to the presence of methane in Jupiter's middle stratosphere. The team suggests either that the stratosphere now contains gases like water, ammonia, and hydrogen cyanide which efficiently radiate energy to space, or that a high-altitude haze above the impact zone is reflecting enough sunlight to keep the gases below relatively cool.