Cosmos - Carl Sagan [82]
We do not know the reason for the reddish-brown color of Jupiter. Perhaps it is due to the chemistry of phosphorus or sulfur. Perhaps it is due to complex brightly colored organic molecules produced when ultraviolet light from the Sun breaks down the methane, ammonia, and water in the Jovian atmosphere and the molecular fragments recombine. In that case, the colors of Jupiter speak to us of chemical events that four billion years ago back on Earth led to the origin of life.
Day 647 The Great Red Spot. A great column of gas reaching high above the adjacent clouds, so large that it could hold half a dozen Earths. Perhaps it is red because it is carrying up to view the complex molecules produced or concentrated at greater depth. It may be a great storm system a million years old.
Day 650 Encounter. A day of wonders. We successfully negotiate the treacherous radiation belts of Jupiter with only one instrument, the photopolarimeter, damaged. We accomplish the ring plane crossing and suffer no collisions with the particles and boulders of the newly discovered rings of Jupiter. And wonderful images of Amalthea, a tiny, red, oblong world that lives in the heart of the radiation belt; of multicolored Io; of the linear markings on Europa; the cobwebby features of Ganymede; the great multi-ringed basin on Callisto. We round Callisto and pass the orbit of Jupiter 13, the outermost of the planet’s known moons. We are outward bound.
Day 662 Our particle and field detectors indicate that we have left the Jovian radiation belts. The planet’s gravity has boosted our speed. We are free of Jupiter at last and sail again the sea of space.
Day 874 A loss of the ship’s lock on the star Canopus—in the lore of constellations the rudder of a sailing vessel. It is our rudder too, essential for the ship’s orientation in the dark of space, to find our way through this unexplored part of the cosmic ocean. Canopus lock reacquired. The optical sensors seem to have mistaken Alpha and Beta Centauri for Canopus. Next port of call, two years hence: the Saturn system.
Of all the travelers’ tales returned by Voyager, my favorites concern the discoveries made on the innermost Galilean satellite, Io.* Before Voyager, we were aware of something strange about Io. We could resolve few features on its surface, but we knew it was red—extremely red, redder than Mars, perhaps the reddest object in the solar system. Over a period of years something seemed to be changing on it, in infrared light and perhaps in its radar reflection properties. We also know that partially surrounding Jupiter in the orbital position of Io was a great doughnut-shaped tube of atoms, sulfur and sodium and potassium, material somehow lost from Io.
When Voyager approached this giant moon we found a strange multicolored surface unlike any other in the solar system. Io is near the asteroid belt. It must have been thoroughly pummeled throughout its history by falling boulders. Impact craters must have been made. Yet there were none to be seen. Accordingly, there had to be some process on Io that was extremely efficient in rubbing craters out or filling them in. The process could not be atmospheric, since Io’s atmosphere has mostly escaped to space because of its low gravity. It could not be running water; Io’s surface is far too cold. There were a few places that resembled the summits of volcanoes. But it was hard to be sure.
Linda Morabito, a member of the Voyager Navigation Team responsible for keeping Voyager precisely on its trajectory, was routinely ordering a computer to enhance an image of the edge of Io, to bring out the stars behind it. To her astonishment, she saw a bright plume standing off in the darkness from the satellite’s surface and soon determined that the plume was in exactly the position of one of the suspected volcanoes. Voyager had discovered the first active volcano beyond the Earth. We know now of nine large volcanoes, spewing out gas and debris, and hundreds—perhaps thousands—of extinct volcanoes