No. 53: Sep-Oct 1987
From Saturn. Micrometeorites constantly chip away at Saturn's C-ring. Using current micrometeorite-flux estimates, the age of the C-ring is between 4.4 and 67 million years. Compared to the purported age of the solar system, 4.5 billion years, Saturn's C-ring (and perhaps the other rings, too) is a brand-new feature. Where did it come from? Is it related to the icy comets that seem to be raining down steadily on the earth's atmosphere? (Northrop, T.G., and Connerey, J.E.P.; "A Micrometeorite Erosion Model and the Age of Saturn's Rings," Icarus, 70:124, 1987.)
From Mars. Inside the vast Valles Marineris Canyon complex, Viking Orbiter photos have picked out wind-blown patches of dark material. These patches are strung out along faults for some 200 kilometers. Astronomers believe they are volcanic vents, which are a scant few million years old. (Anonymous; "Recent Volcanism on Mars?" Sky and Telescope, 73:602, 1985.)
Comment. Another of the surprisingly large number of youthful features in the solar system.
From Europa. The surface of Europa, one of Jupiter's large Galilean satellites, seems to be covered with a relatively smooth veneer of ice. Beneath this frigid skin, according to one theory, lie about 100 kilometers of liquid water. Why hasn't this water frozen completely, given the trifling sunlight at Jupiter's distance from the sun? Tidal stresses provide some heat but not enough; unless, of course, Europa's orbit was much more eccentric in recent times. (Anonymous; "Oceans under the Crust of Europa," Sky and Telescope, 73:602, 1987.)
Comment. An alternate possibility is that Europa's ice and water inventories are recent acquisitions, like Saturn's rings!