March 10, 2007
Alien Volcano in Our Own Backyard
Andy Cheng has seen it all. The scientist from Johns Hopkins' Applied Physics Lab has worked on the Galileo mission to Jupiter, the Cassini mission to Saturn, the NEAR mission to asteroid 433 Eros and many others during his decades-long career. Alien vistas are old hat to him.
But even he was amazed when he laid eyes on this photo of Io's Tvashtar volcano, taken Feb. 28th by the New Horizons spacecraft:
LORRI is an 8-inch telescope onboard New Horizons, NASA's Pluto-bound spacecraft. "The telescope was designed to take high-resolution pictures of Pluto and its moons when New Horizons reaches the outer solar system in 2015," explains Cheng, the principal investigator for LORRI, which is short for Long Range Reconnaissance Imager.
Last week New Horizons flew past Jupiter for a quick velocity boost, and "this gave us an opportunity to take some pictures," he says. Cheng and colleagues trained the telescope on Jupiter's moons Io, Europa, Callisto and Ganymede and on Jupiter itself. Many of the pictures are stunning: gallery.
"Future LORRI images of Pluto and Charon will have even more detail and higher resolution, because New Horizons will bring us at least a thousand times closer than we came to Io," notes Cheng. Of course, no one has any idea what LORRI will see, because Pluto has never been visited by a space probe. "That's why we're going."
Catching a volcano blowing its top on Io isn't really a big surprise, notes Cheng. "Io is in a constant state of eruption."
To understand why, he suggests, dig a paperclip out of your desk drawer. Flex the clip rapidly back and forth many times, and touch the flexure. Careful! It's hot. The combination of flexing + internal friction heats the clip to surprisingly high temperatures.
The same thing happens to Io. Gravitational forces exerted on Io by Jupiter and the other large moons raise tidal bulges in Io's solid crust 30 meters high. This flexing action, like the flexing of a paperclip, makes Io's interior molten hot and, as a result, the moon has hundreds of active volcanoes.
"We were actually hoping to catch a different volcano"”Prometheus," says Cheng. Prometheus is an old and reliable volcano on Io which has been photographed many times before by Voyager and Galileo. It appears in the New Horizons photo, too; "It's the little mushroom-shaped plume at 9 o'clock," he points out.
Tvashtar's plume dwarfed grand old Prometheus, rising 180 miles (290 km) above Io's surface. (For comparison, volcanoes on Earth spew their gas and dust just a few miles high.) "The patchy and filamentous structure seen in the Tvashtar plume suggests to me that condensation from gas to solid particulates is occurring," he says. In other words, the gas could be crystallizing in the cold space above Io to form a kind of sulfurous snow.
Volcanoes spewing snow? It is an alien world.
On to Pluto!
On the Net: