Image credit: NASA/Galileo

Explanation: What would it look like to peer into one of the volcanoes currently active on Jupiter's moon Io? The caldera of Tupan Patera, named after a Brazilian thunder god, reveals itself to be a strange and dangerous place, replete with hot black lava, warm red sulfur deposits likely deposited from vented gas, and hilly yellow terrain also high in sulfur. The robot spacecraft Galileo currently orbiting Jupiter provided the above vista late last year when it swooped by the active world. Tupan Patera is actually a volcanic depression, surrounded by cliffs nearly a kilometer high. The width of the depression is about 75 kilometers. As Galileo has filled its mission objectives and is running low on maneuvering fuel, NASA plans to crash the spacecraft into Jupiter during 2003. 

Illustration Credit: NASA/JPL

Image credit: NASA/Galileo Pele

Prometheus

Culann Patera

These two clips are taken from the top image taken by Galileo. They show two major volcanoes in the process of erupting. The black plumes are clear and the one on the right shows fresh lava. The orange red lava is mainly sulfur, as is the yellow material covering most of IO, literally fire and brimstone...

"Known as Io's "Old Faithful", the Prometheus volcano has been active during every observation of it since it was first seen by Voyager 1 in 1979. The Prometheus plume is 80 km (50 miles) tall, and although its size and shape have remained constant over the years, its plume location has migrated about 85 km (53 miles) to the west. Its volcanic field is similar to those of Hawaiian volcanoes, but it is much larger and more active. The bright, ring shaped deposit around the volcano forms when sulfur dioxide, ejected during the plume eruption, condenses into snow and falls back to the surface. Scientists have been especially interested in determining whether the Prometheus plume is erupting from a vent at the west end of the dark lava flow, or if it is being produced by advancing lava as it flows over a surface rich in sulfur dioxide. New images have helped to resolve this question." - Source

Image credit: NASA/Galileo

Explanation: What causes the unusual colors surrounding Io's volcanoes? Io, the innermost large moon of Jupiter, is known to be the most tumultuous body in the Solar System. Approximately the size of Earth's Moon, Io undergoes nearly continuous volcanic eruptions from an interior heated by gravitational tides from Jupiter and Jupiter's other large moons. The robot spacecraft Galileo currently orbiting Jupiter has been monitoring the active volcano Culann Patera over the past few years. The above images indicate that the volcano has produced not only red and black colored lava flows, but yellow sulfur patches from explosive plumes. Green colors may arise when these processes affect the same terrain. White patches may be caused, in part, by sulfur dioxide snow. As Galileo has fulfilled its mission objectives and is running low on maneuvering fuel, NASA plans to crash the spacecraft into Jupiter during 2003. 

Image credit: NASA/Galileo

Io's atmosphere's most unusual feature is that it condenses as ice onto the surface at night and evaporates back into the atmosphere by day. Because Io rotates on its axis once about every 42 hours, the patch of atmosphere follows the sunlight around Io while the night-time vacuum moves around towards the opposite side. With atmosphere on one side of Io and vacuum on the other, permanent strong winds, approaching the speed of sound, blow perpetually from the sunny side to the dark. Because the atmosphere is so tenuous, these winds blowing at hundreds of miles per hour do not seem to move much dirt or other rubble on Io, although there may not be much rubble to move because the surface of Io is frequently resurfaced with fresh lava. "  - Source

Image credit: NASA/Galileo

In the image above, the orange and white areas on the left side are places where hot lava has recently erupted. The two small white spots are places where molten rock is exposed at the surface near the edges of the lava flows. The long, yellow and orange stream is more than 60 km long and is a cooling lava flow.  The dark deposits in the vicinity of the active flows were not seen in the image taken in the November, 1999 flyby." - Source

The white color in the picture is predominantly sulfur dioxide "snow", though recent discoveries indicate some may be sodium or potassium chloride deposits {salt}. The yellow deposits are sulfur. The atmosphere consist of mainly sulfur dioxide, so the whole planet would have that distinctive rotten egg smell.