Phil
Sulfuric acid subsurface streams
Thu Feb 12, 2004 01:12
12.45.169.251

In reviewing the Moc pictures under the categories of pits and flow features, I noticed something peculiar. There are a great number of collapse features on Mars. These were explained by the capable Dr. Malin as being due to crustal extension followed by collapse to produce the pit chains. This is good as far as it goes, but it does not go far enough. The chasm features "grade into" pit features. Indeed, it looks to me like many of the chasms owe their origin to pits that coalesced. Pits can be seen along their edges and in the terminal zones. Another unexplained feature is how the chasms just seem to abruptly end (some at pits). Other flow features, such as the Olympia Fossae region, are more clearly due to flow. In one photo I saw a feature that puzzled me. A higher up stream crossed over a much deeper valley, which would mean the deeper stream was more recent, no problem there. But in the bottom of the deeper stream, the crossing stream bed could still be clearly seen. This puzzled me until I realized this could only be explained by SUBSURFACE FLOW AND DISSOLUTION FOLLOWED BY COLLAPSE. One cannot tell which stream was older, only that they both formed before the collapse. There are volcanoes there. One would expect Mars to have had more light elements than Earth, more water and more sulfur. Sulfuric acid as dilute solutions, could exist at the surface (also brines as Winston mentioned). This could be what is leaking out of the subsurface to form the Gullies and active Streaks.

Other Questions:
1. Where is all the dust, eroded over billions of years in supposedly dry conditions. Whole plains have been eroded as shown by Dr. Malin. Where did it disappear to?
2. Why dont the pits and craters fill up with dust, since they are natural dust traps?

Answer- the sulfuric acid leaking out of the subsurface zone (which can be seen in the streaks and gullies) flows down into the craters and eats the dust. Most of the flow occurs under the dust, since the acid/brine is dense and viscous. This creates the dark streaks where the flow is sufficient and the angle high enough to wet the dust all the way to the surface. Likewise, higher flows can breach and dissolve the surface to make the gullies. In other words, the mechanism is the same for streaks and gullies, and they grade into each other. It could also be that there is no acid, only water or brine.

Postscript- the small deep pits in Meridiana, are these collapse pits, or are they small craters?