Postcards From The Edge – Galileo Project and planet Jupiter – Brief Article
A half-billion miles from Earth, the feisty spacecraft Galileo astonishes us with flybys of Jupiter’s bizarre moons
Few space probes have had worse luck than Galileo. Built with late-1970s technology to explore Jupiter and its planet-size moons, it arrived some seven years late in the wake of the space shuttle Challenger explosion. Finally sent on its way in 1989, but with a low-power rocket, it was saddled with a convoluted 2.4-billion-mile slingshot trajectory that took more than six years to complete. Along the way the orbiter’s giant primary antenna refused to deploy, and its antiquated tape-drive memory system jammed.
But Galileo is nothing if not plucky. Ground controllers have worked near miracles to keep the craft limping along, returning images so exotic they exceed imaginings. The crippled platform has succeeded in documenting a startling solar system within our solar system, where massive volcanoes blow their tops with astonishing regularity, lightning arcs hundreds of miles at a time, ice-covered oceans grind together to form breathtaking patterns, and all the right conditions may be in place to create life.
In a final burst of glory in November, Galileo will plunge into Io’s highly charged atmosphere, searching for close-ups of that molten moon’s surface. The flight is likely to be the end for Galileo but just the beginning of reasons to keep going back to these compelling worlds.
Callisto has one of the most battered and scarred surfaces in the solar system, the result of 4.6 billion years of abuse from incoming asteroids. Unlike its sibling moons, Callisto has no large-scale processes for erasing craters; some may fade as the underlying ice evaporates, but most simply sit on top of: earlier scars. Still, something mysterious is going on beneath the dusty crust of this ball of ice and rock. During a recital flyby, Galileo detected a magnetic field that indicates a salty ocean.
HOW BIG IS BIG?
The four largest Jovian moons may be dwarfed by Jupiter, but so is Earth. All are vast worlds. Ganymede, some 3,200 miles across, is bigger than Mercury; all the moons are larger than Pluto.
Images of a shattered landscape led researchers to a remarkable conclusion: Europa’s surface is littered with icebergs frozen in place.
Icy material uncovered by recent asteroid impacts shows up red in an infrared image of Callisto.
The interiors of Io, Europa, Ganymede, and Callisto. While three of the moons have metallic cores similar to Earth’s, Callisto has a mixture of ice and rock at its heart. Europa, Ganymede, and Callisto may contain hidden oceans.
MOON OF FIRE
Pockmarked with volcanic calderas and stained with sulfur, Jupiter’s fiery moon Io is home to three dozen active volcanoes. One, Prometheus, may have erupted constantly for the past 18 years. Pillan, which Galileo captured on the horizon in mideruption, is one of the hottest, with lava temperatures reaching 2600 degrees. Where does all the energy come from? Scientists believe the tidal pull of Jupiter heats Io. A slight elongation in Io’s orbit changes the amount of gravitational pull working on the moon over the course of its 42-hour month. This repeated squeezing creates a huge amount of internal friction, heating up the moon’s core until it becomes a vast glob of molten metal. (A similar, though less intense tidal heating warms the oceans thought to slosh beneath Europa’s icy crust.) In October, Galileo will get a spectacular view of Pillan, looking down on the volcano from only 373 miles, just four times higher than the plume itself. A second pass, in November, will be lower.
COPYRIGHT 1999 Discover
COPYRIGHT 2000 Gale Group