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Study on CO2 forming gullies
SFJCody
post Jun 12 2013, 12:25 PM
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Nick Hoffman's 'white Mars' [partially] vindicated?

http://www.bbc.co.uk/news/science-environment-22869184

http://www.sciencedirect.com/science/artic...019103513001668

QUOTE
Long thin grooves - called gullies - on the surface of Mars may have been made not by water but by blocks of frozen carbon dioxide - dry ice.


Funny how old hypotheses can come back again. We've had a decade+ in which the consensus has been that the gullies are formed by liquid water, but now CO2 is a possible instigator again, albeit in the form of solid blocks rather than liquid flows. What with this and other things (such as Edwin Kite's hypothesis for the formation of Aeolis Mons), is the pendulum of scientific opinion swinging away from 'warm, wet, Earth-like Mars' and back in the direction of an alien, colder, only sporadically active world? At least in terms of the overall picture of the planet, admittedly the ground truth from Oppy and Curiosity to date is evidence for a benign, pleasant environment at some points and times in Martian history.

EDIT: Original commentary in the topic title moved to comments section above - ADMIN
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mcaplinger
post Jun 12 2013, 01:39 PM
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QUOTE (SFJCody @ Jun 12 2013, 05:25 AM) *
is the pendulum of scientific opinion swinging away from 'warm, wet, Earth-like Mars' and back in the direction of an alien, colder, only sporadically active world?

One article in Icarus doesn't constitute a fundamental change in scientific "opinion" -- and I'd like to believe that science is not about opinion anyway.

These hypotheses are always worthy of consideration, but testing them may not be possible without more data.


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djellison
post Jun 12 2013, 01:52 PM
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This explains some gullies. It doesn't explain others - especially those with lobate features etc. Given the recent discoveries from Opportunity and Curiosity - it's fairly clear that no - scientific opinion isn't swinging away from a warm, wet early Mars. Indeed - that story is more robust now than ever before.
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SFJCody
post Jun 12 2013, 02:06 PM
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QUOTE (mcaplinger @ Jun 13 2013, 12:39 AM) *
One article in Icarus doesn't constitute a fundamental change in scientific "opinion" -- and I'd like to believe that science is not about opinion anyway.


Well, maybe opinion is the wrong word to use. But as new data has come in over the decades the extent to which Mars can be considered Earth-like has had a few peaks and troughs, with a nadir immediately post Mariner 4.
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djellison
post Jun 12 2013, 02:09 PM
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The case that there was liquid water on the surface for geologically significant periods of time has got stronger in the past decade, and significantly more detailed in the past year. Peaking with Mariner 4? I don't think so.
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SFJCody
post Jun 12 2013, 02:16 PM
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Oh, that's what I want to think. But I like to play devil's advocate because I'm wary of the possibility that I may favouring the evidence that supports my preferred picture of Martian history. I'm sure the nature of things will become clear eventually as more data is acquired and hypotheses put to the test.
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ElkGroveDan
post Jun 12 2013, 02:25 PM
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QUOTE (djellison @ Jun 12 2013, 05:52 AM) *
This explains some gullies. It doesn't explain others - especially those with lobate features etc.

That was my first thought when I read the headline. Clearly however this study makes a distinction of just one kind of gully.
QUOTE
"Linear gullies don't look like gullies on Earth or other gullies on Mars,

QUOTE
A principal clue behind the idea is that the linear gullies end in pits, rather than a fan shape.

Obviously the gullies identified in the earliest MOC images do in fact end in fan shapes, however the images cited in this study really are weird looking and DON'T resemble any terrestrial gullies I've ever seen. Sounds to me like there is plenty of room for two separate discussions on this. Ultimately though this regional observation is a far cry from "vindicating" Hoffman's Mars' global climate history theory -- even partially.


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SFJCody
post Jun 12 2013, 02:40 PM
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Is it perhaps just that we've kind of moved beyond the era of talking about Mars globally in this way and into a complex patchwork of regionally unique stories?
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nprev
post Jun 12 2013, 03:08 PM
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Don't forget about the time variable. Much of Mars' surface is truly ancient, and therefore some processes occurred during vastly different climactic conditions. There may well be more processes of more recent vintage that operated (or continue to operate) today. And of course there may be situational variables for different locales that we're just not yet smart enough to figure out.

Hell, we're still trying to completely understand Earth's geological history, and we live here. Best to keep an open mind & apply the scientific method combined with critical thinking and Occam's Razor; that seems to work pretty well. wink.gif


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serpens
post Jun 12 2013, 11:56 PM
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Ground truth with the MER and Curiosity has pretty well disproved Nick's white Mars hypothesis and in any case gully formation is ongoing (albeit sparce), not a function of a probable warmer, wetter Mars billions of years in the past. Mcaplinger's comments are always sensible and right to the point. All hypotheses are worthy of consideration, but there is insufficient data at this time to narrow down the options.
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