Proof of rivers on Mars

shifty88

http://http://www.npr.org/blogs/thetwo-way/2012/09/27/161896238/streams-of-water-once-flowed-on-mars-nasa-says-photos-prove-it?utm_source=NPR&utm_medium=facebook&utm_campaign=20120927

Interesting article about proof of running water on the surface of Mars. This means that Mars once had a hydrologic cycle similar to what we see on earth.

Ryan_m_b

Leaving aside whether or not there is evidence of this these two statements are missing a cogent argument to support a link between them.

Presence of water is not evidence for a past hydrological cycle.

shifty88

running water itself is evidence of hydrology in itself.

Ryan_m_b

Forgive the pun but that's a world away from an Earth like hydrological cycle

SHISHKABOB

what are some things that could cause running water with no hydrological cycle?

Maybe a meteor hitting the ice cap...?

I mean, since they determined that there was running water because of the fact that the rocks appear to have been smoothed by water and carried in a stream, doesn't that mean that the water must have been flowing for a relatively long time?

Ryan_m_b

Simplistically the hydrological cycle involves storage in oceans/land, evaporation into the atmosphere, precipitation and run off back to sites where it can begin the cycle again. There's no evidence that this happens on Mars and running water itself is not indicative of an Earth like cycle which was what the OP asserted.

As for why water would run on Mars I'm no expert but perhaps freeze/thaw cycles that modify the landscape until stored water begins to run from one place to another. Hardly the same.

shifty88

Seems like the logical conclusion; after all there's lots of orbital photographs with evidence of running water on Mars. I don't have to tell you that water pools at the lowest point, and that water must of been going somewhere for sometime to erode bedrock like that, there must had been some sort of 'resupply'.

Why would the cycle be different on another planet. Titan has liquid lakes of methane and methane rainfall. Not a hydrological process I know; but the process is the same. perhaps suggesting some kind of natural process, why would you assume the natural process' ends 50 miles up.

marty1

Correct me if I am wrong, but don't lava flows erod rock like flowing water too?

seanscon

my two cents:

Mars _does_ have a water cycle albeit *not* earthlike. What happens is that the polar cap, does not just melt, it vaporizes, releasing carbon dioxide and water vapor in the summer hemisphere, and that results in highspeed winds. this wind drives dust, and ice crystals and water vapor and anything in its way to the other hemisphere, where it mixes with the atmosphere there.

in the winter hemisphere, up to 40% of the atmospheric volume is frozen in CO2 polar caps.

water clouds and rain ALSO seen in mars, but that water binds itself with permafrost.

that is the present scenario.

Now, we have (arguably) found evidences of running water. first of all this can also mean that there were flash flood and not permanent rivers which etched those riverine geomorphology. but your point is well taken, if there is a transport of water, then there must be some kind of cyclic activity, albeit not necessarily earth like. These channels can also be the signatures of a retreating ice age.

unless i see the full topography fo the complete channel, i can not draw a conclusion. i would be able to draw a conclusion, if the rover followed the channel , and made study of it - from end to end

seanscon

there is another factor coming to play, the temperature, and the erosion by lavaflow erosion is rather changing the chemical signature of the contact zone (consider that rocks are poor conductors), and often lava is more viscous than water hence flow is very very slow, hence you will not expect a mechanical erosion like water. for fast flowing lava, it cools down fast too, and a new layer of lava flows over it.

Enthalpy

Could molten rocks get round shapes, without any water flow? Just from volcanic eruptions or from a meteoroid impact?

Solon

I found it very disappointing, and rather strange, that a mission designed to look for past signs of life, finds what is apparently an ancient river bed, complete with pebbles, and doesn't spend more time, and use the macro camera, to try and identify the rock type of those pebbles. Nothing to see here, move along? I thought they would have been jumping with joy at such a discovery.

seanscon

@ enthalpy, i am afraid, no. a lquid will take a round drop shape only when
1) either it has a high surface tension, and the medium it is on has a low adhesion (mercury and glass for example) - for lava on rock that is not the case
2) in microgravity, in mars that is not the case either.

H2Bro

If you have water running downhill, it was deposited uphill by some process. Ergo, you have a hydrological cycle.

If you have a drug user and a drug seller, you have a drug trade.

No reason to suppose it's earth-like, though.

shifty88

looks like my two lined statement caused some debate.
found this article on the hydrological cycle.
havn't read it yet but should prove interesting to to those who are interested
Enjoy
http://www.agu.org/journals/ms/ms1203/2011MS000069/