I'm really, really cautious about MOLA maps.

They are gorgeous, but they are terribly deceptive. First of all, their color coding for elevation makes the surface of Mars appear (wrongly) as another "ocean world." This is a significant problem.

* I know, but it does give a good perspective on elevations.

Also, the renderings of the MOLA maps grossly exaggerate the appearance of surface relief. This tends, for example, to make craters look much deeper than they really are -- and fresher too.

* Yes, but...

As for Viking renderings, some of the same cautions need to be applied. As a rule, Viking renderings have been subject to extreme contrast stretching, which has the effect of grossly distorting the surface appearance such that all features seem fresher, sharper-edged, and altogether more lunar-like.

* ...but, (imho), the Viking B&W images also reveal older impact events pretty clearly (in Oxia!).

The MOC map I linked to is based on moderately stretched images from the Mars Orbiter Camera, much closer to the actual visual appearance of the Martian surface than anything that has been produced to date.

I have no doubt that most of the large craters in Oxia are the result of impact.

* OK(!)

But what sort of surface and subsurface was impacted?

* From looking at the B&W Viking images (especially), I would say that there was another similar impact event in Oxia.

And did those impacts allow the release of dark (and possibly later light) colored subsurface fluid material? Material which we now see as large-scale deposits, dunes, and so-called "wind streaks"?

* It's very likely.

Are these deposits carbon from asteroids? Nobody knows and current instrumentation doesn't allow finding out. Are they frozen hydrocarbons? Nobody knows, and there's no way to find out at the moment. Are they volcanic deposits? Nobody knows, and right now, there's no way to find out. Are they air-fall deposits? Nobody knows, and there is no certain way to find out at the moment.

Is the standard interpretation correct? That is, are the deposits in these (and other) craters erosional remains of former fill (however it arrived), and are the "wind streaks" seen here and elsewhere actually the result of wind action?

* Yes. (mho)

Seems to me that these are fundamental questions, but I sincerely doubt that more than a handful in the planetary science field sees a career future in asking.

* No, not right now. :) It's a good diversion from what's going on in the world today, B.

Cheers, BFelix

Cheers back.

Marcia