National Geographic : 1985 Jan
explains, "they soften and can flow. Moun tains may actually creep away, like Silly Putty spreading out. Viscous creep on Venus could be at least as effective as water erosion on Earth in reducing mountainous relief. If so, that further implies that all the high fea tures we see on Venus are young." If such bizarre processes as viscous creep dominate our closest neighbor, what alien mechanisms have evolved on more distant bodies? Who would have dreamed up the throbbing, spurting moon Io that Voyager 1 discovered on its way past Jupiter? I remember well the mixture of shell shock and elation among the Voyager team when huge and unmistakable volcanic plumes appeared on images of Io. The rest of the solar system could no longer be regarded as geologically dead. lo, a moon that is tumultuously hot on the NASA(LEFT); JAMES L. AMOS SATURN SHATTERED SATELLITE or failed moon? Foryears, most scientists believed the latter-thatSaturn's remarkablerings were unaccreted materialfrom the planet's nebula, held in eternalthrall to Saturn's gravity. But now, with thousands of close-up imagesfrom the Voyager flybys, scientists are trying anew to explain the rings' amazing complexity. Peter Goldreichof Caltech (above) now thinks they may be of recent vintage. "There's too much going on in there," he says, "for them to have remainedstablefor 4.6 billion years." Instead, some think the rings are remnants of a collision between a Saturnianmoon and an errantcomet. As little as ten meters thick, the rings probably consist mostly of pieces of water ice from pebble to boulder size. Seen from a distance of 1.5 million kilometers, they cast their shadow across the solarsystem's least dense planet only 70 percent the density of water.