Why is Mars not more weathered?

Gwynston

Reading about Curiosity's drilling results and other observations led me to wonder why evidence of past water on Mars is not actually harder to find?

For example, there are already pictures of what are obviously old river beds, and it has been supposed that the clay deposits found in the recent drilling could indicate that curiosity was drilling into an old lake bed. Indeed, the pictures of the bore hole shows that the colour of the material is very different just below the reddish surface.

But doesn't Mars have winds an sandstorms? Why hasn't all this evidence been more eroded away? I know it has a very thin atmosphere, so erosion is probably light, but it's supposedly been billions of years since there was any flowing water. That's a lot of time for erosion to have an effect.

I would have expected pebbled river beds and lake bottoms to be well buried under a lot of dust by now....

shedweller

There probably are a lot of riverbeds buried but wind borne dust also doesn't settle in places where the wind is stronger so you see bedrock. Just think about snowdrifts and how you will also see places where the bare ground is visible, where the wind scours away any snow.

Capt'n Midnight

on earth water is 1,000 times denser than air

On Mars it's way lower ~1%

no idea of the way you corrolate them wrt energy and stuff
but 100,000:1 is like 3 billion years to 30,000 years


anyway the number of meteor craters can be used to tell ages and erosion rates and plate tetchtonics

Wibbs

As the good Capt'n noted the Martian winds are incredibly feeble because the atmosphere is so thin and low pressure. If you could walk about without a spacesuit on the surface, you'd barely register a 200 mile per hour wind on your skin. If you screamed your lungs out, someone could be standing 30 feet away and not hear you. The particles any Martian wind could lift would be tiny, more like talcum powder. On earth winds can even move rocks across dry lake beds under some conditions. So the rate of wind erosion is much much less than on Earth.

Gwynston

Thanks for the replies - interesting stuff!

Certainly the atmosphere is thin now. Do we know how that might have changed over history? e.g. back when there was water, and Mars was warmer with internal heat still fueling things, do we know if the atmosphere was more complex and more dense?

Myrddin

Gwynston wrote: »

e.g. back when there was water, and Mars was warmer with internal heat still fueling things, do we know if the atmosphere was more complex and more dense?

I'd imagine so, my understanding of it is that when the core cooled, Mars would have lost its magnetic field which thus left its atmosphere to be decimated by solar wind...

shedweller

EnterNow wrote: »

I'd imagine so, my understanding of it is that when the core cooled, Mars would have lost its magnetic field which thus left its atmosphere to be decimated by solar wind...

They say its magnetic field is patchy and has poles all over the place. Completely unlike our magnetic field.

Myrddin

shedweller wrote: »

They say its magnetic field is patchy and has poles all over the place. Completely unlike our magnetic field.

As in currently, or when the planet was geologically active {core still molten}?

shedweller

Currently, afaik.

Capt'n Midnight

as far as we know only Earth has tectonic plates that move - iirc it's to do with organisms depositing shells on the ocean floor

volcanism has been seen on lots of moons
Venus has had recent volcanism (recent relative to 4 billion years)

volcanism is powered by temperature differences
you can have mud volcanoes, sulphur volcanoes and even liquid nitrogen volcanoes

shedweller

Tectonic plates are the result of magma flowing underneath. It drags the crust of the earth in different directions which breaks up the crust.

littlemac1980

I was reading recently about Enceladus, and I think there is quite a bit of evidence to suggest it is tectonically active.

Capt'n Midnight

shedweller wrote: »

Tectonic plates are the result of magma flowing underneath. It drags the crust of the earth in different directions which breaks up the crust.

yes , but IIRC there is a biological role involved

maybe I'm getting mixed up with volcanism, anyway it's a Gaia thing
http://en.wikipedia.org/wiki/Subduction

Geophysicist Don L. Anderson has hypothesized that plate tectonics could not happen without the calcium carbonate laid down by living beings at the edges of subduction zones. The massive weight of these sediments could be softening the underlying rocks, making them pliable enough to plunge

shedweller

Capt'n Midnight wrote: »

yes , but IIRC there is a biological role involved

I must look up that, thanks.:)

ps200306

I thought that subduction needed water for lubrication and that this was one of the reasons why the surface of Venus is so geologically young. The runaway greenhouse evaporated all the surface water which knackered the plate tectonics. Without plate boundaries as an exit route for energy from the mantle, the surface heats up and periodically melts entirely and overturns. I could be dreaming it.