Saturn in eclipse

Yes, this is a real picture. More accurately, it’s 165 pictures pasted together from NASA’s Cassini spacecraft’s flyby of Saturn as the planet between the probe and the sun. From this unique vantage point, the contrast of light and shadow enabled astronomers to discern new bands of ice and dust — perhaps the remnants of a shattered moon — between the inner and outermost edges of the ring system. This panorama reveals Saturn casting a massive shadow some 75,000 miles long over Cassini’s camera. Though the brightness in this image has been enhanced to reveal detail, the photo’s sharp contrasts owe foremost to the millions of square miles of orbiting ice crystals that ring the planet. The dark gaps between the bands are thought to be the result of gravitational forces exerted by the planet’s many moons, but these forces are not the only cause. The Encke Gap, among the largest of these vacuous rings, is maintained by Saturn’s innermost moon and “ring shepard,” Pan, which plows through the orbiting field of ice and dust.

Image courtesy CICLOPS team.

This deep, dark region retains heat from the hot gas and dust that formed Earth about 4.5 billion years ago.

The middle layer, the mantle, is solid rock, but it is hot enough to flow slowly, like Silly Putty. The movement, called convection, brings hot rock from the lower mantle to the surface. Cooler rock at the top of the mantle sinks.

The overall effect of convection is to create “conveyor belts” that transport the giant plates that form Earth’s crust. Mantle rock rises close to Earth’s surface along the mid-oceanic ridges. Some of the mantle rock melts, rises further, and, and where melt forms, rises, warms rock above it, which cools crystallizes to and to forms new ocean crust. As ocean the new crust moves away from a ridge, it cools and become denser, eventually sinking back into the mantle.

“As the continental plates are carried along on this conveyer belt, they may crash together (the Himalayas), slide past one another (California), or separate (Baja California),” says Goodwin. Over hundreds of millions of years, the continents have merged and re-separated in their continual movement around the globe. This movement explains why fossils of tropical animals are found in Antarctica, she says.