No. 62: Mar-Apr 1989
Most of the Martian surface is thought to be more than 3.8 billion years old. This portion is densely cratered from a period pf heavy meteorite bombardment. It is also carved by many channels that are thought to have been cut in ancient times by flowing water, water which quickly escaped into space or combined chemically with Martian minerals. The present atmosphere of Mars, in consequence, contains little water vapor.
But some of the Martian landscape, notably Alba Patera, raises questions about the above scenario. The anomalous characteristic of Alba Patera is its relative smoothness and scarcity of impact craters. This Martian real estate is believed to be 2 billion years younger than the rest of the planet. Even so, it, too, is marked by "fluvial" features that resemble stream beds.
Question #1. How did Alba Patera get smoothed out or "reworked"? In other words, what happened to the ancient craters that must have pocked its surface, as they do everywhere else?
Question #2. Where did the water come from to cut Alba Patera's stream beds if all of the Martian water disappeared 2 billion years earlier?
One line of thought maintains that "fluvial" does not mean "pluvial," and that Martian water has come from below rather than as rain from the atmosphere. Both fluvial episodes, in this view, occurred when something caused the Martian crust to release huge quantities of stored water. Hydrothermal activity is mentioned as a possibility.
(Eberhart, J.; "The Martian Atmosphere: Old Versus New," Science News, 135:21, 1989.)
Comment. Another speculation is that immense quantities of Martian water are tied up in methane hydrate and is released when the ambient temperature is somehow increased or perhaps by seismic activity.
Reference. Anomalous characteristics of the Martian surface are cataloged in chapters AME and AMO in our catalog: The Moon and the Planets. Details here.