Hello Nick -

No doubt the deutrium/hydrogen ratio is a key to understanding the mechanics of accretion in our solar system. No doubt also that the craters are key to the timing and thus the understanding Martian "geology" (marseology?). Finally, no doubt that the strong desire to find liquid water on Mars almost hopeleslly interferes with any rational analysis of the data.

First off, I wonder if the distillation of Mars atmosphere by the solar wind is the sole means of enrichement. Neither Mars nor Venus have magnetic fields to deflect this wind, and I wonder whether the deutrium may simply be being delivered from our Sun.

Alternatively, given this lack of magnetosphere, perhaps the Sun may be delivering protons which collide with hydrogen to form deutrium.

I also don't know about the deutrium ratios of comets. While the probes to them may have indicated a "normal" deutrium/hydrogen ratio, if I remember correctly the carbonaceous chondrites show deutrium enhancement, which may simply be the result of these dead comets loss of hydrogen during their travels through the inner solar system, or perhaps their acquisition of deutrium during those travels.

Whatever the case, I have to agree with you that the "data", such as it is, does not add up to form a coherent view of marseological processes. I believe that the key breakthrough is going to be when those in the field finally understand that large impacts release large amounts of the gases and volatiles which are held in Mars' crust, and further that these large impacts occur on a chaotically cyclical basis.

ep