Like all of you, I'm excited about the fine-scale resolution MRO will provide. But something nags at the back of my mind...

I have read my copy of Don Wilhelms' "To a Rocky Moon" so often that it is in tatters... and I'm struck by one of Wilhelms' overriding conclusions from his experience in lunar exploration:

Fine-scale resolution doesn't always help you understand the geologic processes that formed a planetary surface.

Wilhelms makes the point repeatedly that, in analyzing lunar geologic processes, lower resolutions and larger scales were much more instructive than extremely high-resolution imagery. His point of view was that the high-res stuff from the LO program was mostly useful to the Apollo planners in characterizing landing site qualities, but that for scientific analysis, LOs 4 and 5, with their higher orbits and larger-scale images, were *far* more valuable.

The question I have for all of you professional (and amateur) astrogeologists out there is this: Would this observation apply to Mars as well as our Moon?

My own tentative answer to that question is... yes and no. I think that Mars preserves enough large-scale record of its early impact history (especially in the southern hemisphere) and of subsequent volcanic, climatic and erosional epochs that the larger-scale, lower-resolution imagery available from Viking (and even Mariner 9) may be some of the most useful data we have in identifying the widespread, planetwide processes that have shaped the face of Mars.

But on Mars, unlike on the Moon, there are questions of climatic history and change that can only be read at very fine scales. The Moon presents a boringly similar surficial appearance across its entire surface -- the erosional processes there are very specific and limited, and result in a fairly homogenous surface appearance regardless of the underlying geological units. This is not true of Mars, where tectonic, volcanic and climatic activity not only had a hand in shaping the planet over billions of years, but (to some degree) continue to this very day.

However, like the Moon, the surface of Mars doesn't always present clear-cut contacts from one geologic unit to another when you get down to fine scales. Like the Moon (and like Earth, for that matter), processes both constructive and destructive have in many places jumbled and made "messy" the surficial layer's relationship to its underlying units.

So... in our quest for higher and higher resolution, do any of you think we should heed Wilhelms' warning that such a desire can blind us to seeking data at more "useful" scales? Or do you think that Mars, being a different planet with a far different history, requires more investigation at finer scales than the Moon does?

-the other Doug

Thats the genius of MGS, Odyssey and MRO...

MGS does 250m/pixel with its context imager, and 1.5m/pixel with MOC
Mars Odyssey does 12m/pixel in Visible, and 100m/pixel in IR
MRO will do 0.3m/pixel with HiRise, 6m/pixel with CTX and global colour imagery with MARCI at a couple of K/pixel....

So we have imagery at

K's/pixel
100's m/pixel
12m/pixel
6m/pixel
1.5m/pixel
0.3m/pixel

Just about every order of magnitude from a medium pizza to a small county

Doug

The problem on the moon is that local geologic detail has been cratered to death.

Once you get down to the size where the surface is saturated with a steady-state population of craters, there is little to gain with raw photo resolution, unless you have humans and/or rovers working on the ground.

If you had very high signal-to-noise multispectral data for studying compositional mixing, and high resolution day-night thermal data for mapping thermal properties including ejecta blankets and soil maturity and block abundances, yes, that would help sorting out the "Monte Carlo Geology" and picking better samples.

The highlands are worse than the mare...the jumble is multi-generational. Apollo 16, for example, had 1.) Ancient highland mega-regolith cratering 2.) Nectaris and Imbrium ejecta blankets deposited on and mixed into the megaregolith, and 3.) Post Imbrium churning of the landscape by saturation cratering forming a 5-10 meter post imbrium regolith.

Unconsolidated highland materials forming non-sintered regolith also "creep" with impact gardening and seismic shaking and perhaps thermal cycling. "Volcanic" interpretators of lunar geology plausibly but incorrectly interpreted the "Flamsteed Ring" ghost crater that Surveyor 1 sits inside (on mare) as younger than the enclosed mare as the mare has more craters than the crater ring hills, and the crater ring hills clearly have flowed *ONTO* the mare.... this was creap of the thick regolith on the hills down onto the mare lava flows that embayed them, and the young mare in this region (with an estimated 1 meter regolith) preserves small craters far better than thick regolith on the hill slopes.

"His point of view was that the high-res stuff from the LO program was mostly useful to the Apollo planners in characterizing landing site qualities"

I think that is a part of the HiRise mission: looking for suitable landing spots.

Yup - the difference between Surveying and Recon work I guess

Doug