Astronomy Picture of the Day

Explanation: What makes the colours in Jupiter's clouds? With a mean temperature of 120 degrees Kelvin (-153 degrees Celsius) and a composition dominated by hydrogen (about 90%), and helium (about 10%) with a smattering of hydrogen compounds like methane and ammonia, the blue, orange, and brown cloud bands and the salmon coloured "red" spot are hard to explain. Trouble is -- at the cool cloud temperatures Jupiter's atmospheric constituents should be colourless! Some suggest that more colourful hydrogen compounds well up from warmer regions in the atmosphere, tinting the cloud tops. Alternatively, compounds of trace elements like sulfur may colour the clouds. Jupiter's colours do indicate the clouds' altitudes, blue is lowest through red as highest. The dark coloured bands are called belts and the light coloured ones zones. In addition to the belts and zones, the Voyager missions revealed the presence of intricate vortices visible, for example, in this 1979 image from the Voyager I flyby. Centuries of visual observations of Jupiter have revealed that the colours of its clouds are ever changing.