Marcian River?!? Bleh, What Marcian River???

[admiral_ju00]

I like to dedicate this to ExtraSense if he's still around:

 

Courtesy of Nature.com

 

 

Dust rocks martian river theory

Philip Ball

Signs of water may really be slumping sand.

 

Feature like this have been cited as evidence for recent water flows on Mars.

© NASA

 

Gullies on Mars that appear to have been carved by flowing water could instead have been created by landslides of dry powdery material, scientists have found.

 

Troy Shinbrot and colleagues of Rutgers University in New Jersey say that Mars's smaller gravity, which is 38% weaker than Earth's, would allow rockfalls to last longer than they do on Earth. This means landslides could cause the kind of geological features usually only associated with running water.

 

The researchers doubt that all martian "rivers" can be explained away like this, but the theory could account for some of the most puzzling and provocative examples.

 

Spacecraft in the 1970s were the first to see Martian geological features that resembled dried-up riverbeds. This helped establish the theory that the surface of Mars once held rivers, lakes and even oceans.

 

NASA's Mars Rover missions, which touched down on the red planet in January, uncovered geological evidence that there was indeed liquid water on Mars, a very long time ago. That confirmed what many already believed.

 

But four years ago, the Mars Global Surveyor spacecraft astonished planetary scientists by taking pictures of gullies and channels that seemed to have been formed in the relatively recent past: a few million years ago, or even less.

 

Those pictures have led some researchers to propose that Mars might still experience outbursts of liquid water today, perhaps by the sudden venting of underground reservoirs. Yet perplexingly, these young gullies are found in regions of the planet that are always very cold.

 

Now Shinbrot and colleagues say the more recent features might not be sculpted by water at all, but could be the result of flows of dry mineral grains, like slumping sand.

 

Dusty answer

During a landslide in dry sand, the grains are borne along in air and flow rather like a liquid. But the idea that such flows could have produce the river-like gullies on Mars has not been taken seriously, because the grains generally settle out of the air quite quickly and the flow does not get far.

 

But Shinbrot points out that in a weaker gravitational field, this settling happens more slowly. Furthermore, Mars's thinner atmosphere would mean that moving grains experience less drag than on Earth, and so they might travel faster.

 

To investigate the consequences of these differences, Shinbrot and colleagues looked at landslides in a powder of tiny, hollow ceramic beads, just 4 thousandths to 90 thousandths of a millimetre across1. Because these grains are so light, they flow more quickly than they settle. The researchers estimate that the same will be true of sandy grains on Mars.

 

Miniature landslides in these feather-weight, hollow grains produce a range of distinctive shapes that echo those seen, at much larger scales, on Mars. For example, one experiment produced a ridge fringed with narrow, parallel gullies separated by long hillocks, in a comb-like pattern. Something very similar was seen by the Mars Global Surveyor around the edge of a depression called the Polar Pit. At that time, the channels were interpreted as evidence of flowing water.

[Skye]

Another hypothesis is that the boiling of dry ice under the surface would release a whole bunch of CO2 which would carry the dust and sand as it sinks into the valleys.

[Cap'n Refsmmat]

He's baaaaaaack!

http://www.scienceforums.net/forums/showthread.php?t=4184