PASADENA, Calif. - As if on an armchair trip back in time, NASA scientists said Friday that the spacecraft Galileo shows that volcanic processes similar to those that wracked the Earth eons ago still rage on Io, one of Jupiters 16 moons.
Newly released close-up images of Io, the most volcanically active body in the solar system, show its volcanoes are larger, hotter and longer erupting than any seen on Earth since halfway through its 4.5 billion-year history.
"Io is providing us with a laboratory where we can just sit and watch the processes we cant see on Earth because they happened a long time ago," said Susan Kieffer, a Canadian geologist and consultant to Galileo scientists.
Galileo flew within 380 miles (611 kilometers) of Io on October 11, snapping the closest-ever images of the moon, a colorful body -- about the size of the Earths own moon -- that is pocked with more than 100 active volcanoes.
The images released Friday focus on three of those volcanoes, Pele, Loki and Prometheus.
The pictures show that Pele, named for the Hawaiian goddess of fire and volcanoes, spews a plume roughly 250 miles (400 kilometers) above Ios surface. At the volcanos center, heat-sensing imagery shows an enormous pool of molten lava nestled in an equally large caldera.
At the edges of the pool, a thin crescent-like line can be seen to stretch for more than six miles (10 kilometers) where the raft of sloshing, yet solidifying, lava strikes the calderas edge, exposing the still-liquid rock beneath. Similar lines can be seen in active lava lakes in Hawaii, although they are 100 times smaller.
"This could be a glimpse of the Earths past," said Alfred McEwen, of the University of Arizona, Tucson and a member of the Galileo imaging team.
Loki, named for the Norse god of mischief and discord, pumps out more heat than all Earthly volcanoes combined. Two of the instruments aboard Galileo show that the volcanos caldera, 125 miles (200 kilometers) wide, is repeatedly flooded by lava, covering an area larger than the state of Maryland, said JPL scientist Rosaly Lopes-Gautier.
The lavas in the caldera hover at a relatively frosty 32 degrees Fahrenheit (0 degree Celsius), but far warmer than the minus 356 degrees Fahrenheit (minus 180 Celsius) temperatures typically found on Ios surface.
Near Prometheus, named for the Titan in Greek mythology who stole fire for humankind, scientists have been puzzled by an enormous plume the volcano has been seen to emit since Voyager 1 flew by the moon in 1979. Since then, the plume has shifted 60 miles (100 kilometers) but has never ceased.
They are now certain that the plume is the effect of flowing lava vaporizing enormous deposits of frozen sulfur and sulfur dioxide. The plumes reach incredible altitudes thanks to Ios low atmospheric pressure and cold temperatures, along with its low gravity -- just one-sixth that of Earths.
Where a shooting geyser might only reach several hundred yards (meters) on Earth, on Io it would travel upward perhaps 15 miles (24 kilometers), Kieffer said.
The new images also show that Ios volcanoes tend to be squat and wide, unlike on Hawaii where they can poke from the ocean floor to form mountains that tower high above sea level.
Io does have its fair share of mountains, however: McEwen said several that are apparently non-volcanic in origin are as high as 10 miles (16 kilometers).
Galileo will fly by Io again on November 25, this time traveling a daredevil 186 miles (300 kilometers) above its surface. That will mark the official end of Galileos mission to Jupiter and its moon, although it could be further extended. A decision is expected by late January.
However, the intense radiation environment near Io could also spell an early end to the mission.
"If we survive it, its conceivable we will see Io again," said Torrence Johnson, the Galileo project scientist at NASAs Jet Propulsion Laboratory.
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