"Mars Water" - The NASA PAO in action

Dale wrote:

Oddly enough, the BBC's report included the probability that it was
CO2, rather than H2O. The New York Times just reported it as
evidence of recently flowing water.



The NASA press release calls it water, and doesn't mention CO2:
http://spaceflightnow.com/news/n0612/06mgs/

Pat

In sci.space.history message , Fri,
8 Dec 2006 18:19:04, Pat Flannery wrote:

That's what hit me as so odd about the press release; if they had said
it was liquid that _may_ have been water, it would have been iffy and
optimistic, but not outright wrong....but they went out of their way to
state it was water and didn't even mention it could also be liquid CO2,
and that was completely, and purposely, misleading.

Liquid CO2 cannot exist at any temperature at terrestrial atmospheric
pressure. The pressure on Mars is of the order of 100 times less. But
free water near the ice-point can exist on Mars without boiling, though
it would evaporate readily.

I forger what the minimum pressure for liquid CO2 is; I believe it to be
substantially more than one Earth atmosphere. That, at Mars' gravity,
corresponds to a depth of substantially more than 30 metres of water.
While liquid CO2 might exist underground, as a melt from a precipitate
subsequently covered with rock/sand,etc. and warmed, I don't really see
it reaching the surface as liquid and flowing as liquid.

A CO2-powered Peleean pyroclastic flow seems possible, or a CO2 geyser,
if there is an adequate mechanism to supply it.

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Dr J R Stockton wrote:


Liquid CO2 cannot exist at any temperature at terrestrial atmospheric
pressure. The pressure on Mars is of the order of 100 times less.
But free water near the ice-point can exist on Mars without boiling,
though it would evaporate readily.

I forger what the minimum pressure for liquid CO2 is; I believe it to
be substantially more than one Earth atmosphere. That, at Mars'
gravity, corresponds to a depth of substantially more than 30 metres
of water. While liquid CO2 might exist underground, as a melt from a
precipitate subsequently covered with rock/sand,etc. and warmed, I
don't really see it reaching the surface as liquid and flowing as liquid.


Back in 2000 when they first spotted the flows, scientists pointed out
that they were coming not from the surface, but from the walls of
craters... and the depth under the surface they were emanating from was
just right for the weight of the overlaying soil to generate the
pressure needed to keep the CO2 liquid.
Once it got out on the surface, the liquid CO2 wouldn't be stable; it
would run downhill while boiling, so that some would become gas and
float off, while the cooling caused by the evaporation as it boiled
would cause the rest to freeze into dry ice.


A CO2-powered Peleean pyroclastic flow seems possible, or a CO2
geyser, if there is an adequate mechanism to supply it.


We already know about the CO2 geysers from pictures of the area near the
south pole:
http://www.seedmagazine.com/news/200...with_carbo.php

Pat