The MARSIS team has a paper by Watters et al. that is being published in the December 14, 2006, issue of Nature. See the Editor's Summary for a synopsis and links.

See also "Geologists finding a different Mars underneath."

For those without access to Nature, and since the EurekAlert release did not show them, check out the related JPL news release for some of the graphics.

With the new SHARAD data coming in, I was wondering if there had been any new press releases with MARSIS. Good to finally see some results. And frankly, what better place to start than with the stark dichotomy between the north and south hemispheres? Few gross Martian surface features are as apparent as the difference between the heavily cratered Southern Highlands and the smoother, significantly lower-lying Northern Plains. That we still haven’t nailed down the basics of Martian crust formation and evolution reminds us how young planetary science still is.

Speaking of really high highs, has there been any new information on the ionosphere sounding since November 30, 2005?

I haven't performed an in-depth search at LPI, but a quick one reveals this abstract, which was presented at LPSC earlier this year. There could be more, especially at other, non-LPI conferences or meetings.

EDIT: I just noticed your handle (NMRguy). Do you have a professional interest in MARSIS data acquisition?

Yeah, you got it. Some of my past research used pulsed RF, but you might say that it was a little more chemical in subject matter. I have since moved on to greener pastures.

IMHO,that still does not explain why only the northern hemisphere has been flooded with lava,leaving the southern hemisphere looking as old as it is!

".... That we still haven’t nailed down the basics of Martian crust formation and evolution reminds us how young planetary science still is."

Actually, it's more a question of having enough relevant data. Before Mars Global Surveyor, essentially all we had on Mars in terms of global geological / geophysical data was black and white and 2-color imaging (3 color stuff from Viking is nearly useless), surface thermal properties, CRUDE topography and low resolution gravity mapping, and scattered radar and other data.

The northern plains are massively resurfaced and mantled. Their original geology is well hidden. The escarpment between highlands and northern plains is massively eroded and modified. Little shows up in gravity data.

MOLA topography suggests that even if we could entirely un-mantle the plains, the actual geological landform record of the processes that formed the highland/lowland dichotomy would still have been substantially cratered to oblivion.

This is a *HARD* problem, and will probably take extensive geophysical and geological traverses down on the surface to solve, together with extensive hard-rock sample return from involved ancient geologic provinces.

We don't know that it has been flooded by lava. In fact, its extremely flat morphology and the absence of wrinkle ridges associated with lava plains elsewhere on Mars and the Moon suggests that has not. I stll think silty or muddy sediments much more likely material overall for the northern plains. Which does not exclude local lavas, ash, etc.

Jon

I am starting to get a feeling that ice-creep driven processes have churned the ice-rich high-latitude terrains so that in the mobile ice-rich zone, stratigraphy and geologic history have been churned and mangled.

I think that is very likely. Does anyone know the modelled depth of the active layer on Mars? Is it centimetres, or metres thick?

However I don't think that is is sufficient to completely smooth the lowlands. The same processes would have operated at the southern polar regions, and we see presrvation of ancient crater geomorphology there, at least at the gross scale. Furthermore we see the smooth northern plains extending to equitorial latitudes, where periglacial processes would have been less intense perhaps.

Jon

Jon:

Remember the difference in altitude and insolation between the two hemispheres, and also the effects of polar wandering; the north and south poles are quite different to this day!

Bob Shaw

That's an interesting question. But changes in obliquity, true pole position, and insolation should average out over a billion years or so. That leaves the altitude difference as the known variable, and the composition of the regolith is the unknown. As I recall there is poygonal terrain in the southern high latitudes as well, so we kno that periglaical action has been happening there. Also the extreme smoothness of the northern plains occurs ar both high and low latitudes, suggesting that the controlling aspect is not latitude, but either composition or altitude, or both (as suggested by the boreal ocean hypothesis).

Jon

"...However I don't think that is is sufficient to completely smooth the lowlands..."

I totally agree. Whether there were ever shallow seas in the northern plains, I think the area has been a persistant site of ice and dust and sand accumulation, to the depths of hundreds of meters. Flooding events that carved great outflow channels may well have dumped vast sheets of mud-water onto the plains, which promptly foze as quick-mud-ice, then has slowly "churned" over deep geologic time that is totally beyond the time scale of terrestrial periglacial processes. I strongly suspect the big boulders MRO is seeing on the plains as it searches for a Phoenix landing site have been "plucked" from more solid rocky terrain under the ice-mud and brought to the surface. We DO NOT understand this terrain if we think of it in lunar regolith or terrestrial polar processes terms and timescales, as two extreme model end-members.