[meteorite-list] Pebbly Rocks Testify to Old Streambed on Mars (MSL)

From: Graham Ensor <graham.ensor_at_meteoritecentral.com>
Date: Sat, 1 Jun 2013 00:39:00 +0100
Message-ID: <CAJkn+ka60C37bpAGhgPe8dQ_ZOSi1ZGF==spnF+tTdaC8wfiog_at_mail.gmail.com>

Hi Larry, that's exactly the word I was trying to look
for..."sublimates"...just could not bring it to mind. (any was being
too lazy to look it up) So my thoughts were right....very unlikely
for there ever to be any liquid CO2 on Mars.


On Fri, May 31, 2013 at 6:32 PM, <lebofsky at lpl.arizona.edu> wrote:
> Hi Graham and Steve:
> Technically, you are wrong--CO2 sublimates (turns from solid to gas) and
> does not evaporate (turns from liquid to gas). The triple point (where
> solid, liquid, and gas exist)of CO2 is 5.1 atmospheres. Since the "sea
> level" pressure on Mars is about 0.006 atmospheres, the atmospheric
> pressure on Mars would have had to have been 1000 times greater than it is
> now. Not very likely. To have liquid water (enough for flowing rivers) the
> pressure would have to be about 0.006 atmospheres at 0 degrees C. In fact,
> I think that this is how they originally defined the mean surface of Mars.
> The only problem is that Mars is generally too cold at this pressure for
> there to be liquid water, so you would need a warmer Mars (by a about 60
> degrees centigrade for the "average" temperature) in order to get water
> flowing on Mars. This is much more likely than a 1000-fold increase in
> surface pressure.
> In fact, there is evidence for liquid water on Mars, but not in great
> amounts (gullies, for example).
> Larry
>> Hi Steve,
>> Liquid CO2 cannot exsist as a liquid at atmospheric pressure. It must
>> be pressurized above 60.4 psi to remain as a liquid....so would it
>> have ever flowed on Mars at all? Solid CO2 evaporates to gas on Earth
>> and I would say it does the same on Mars....somebody correct me there
>> if I am wrong?
>> Interesting thought about bog iron.....we would have hopes on Mars
>> which would be the reverse of our hopes on Earth. Many pieces of bog
>> iron have got folks excited on Earth because they were thought to be
>> meteorites but are meteorwrongs. On Mars we would be hoping that a
>> meteorite was bog iron as that would indicate a bog and thus peat and
>> plantlife. As far as I know bog iron is associated with pea bogs and
>> cannot form just with water...now a layer of old peat bog/coal would
>> be an exciting find on Mars.
>> Graham
>> On Fri, May 31, 2013 at 9:41 AM, Steve Dunklee <steve.dunklee at yahoo.com>
>> wrote:
>>> What is the composition of the pebbles? and other deposits? if there are
>>> not carbonates or other water soluable constiuentes then we may have to
>>> accept the flow of carbon dioxide as the cause of the water like erosion
>>> caused by the heating and cooling on mars. where is the bog iron and
>>> limestone or other precipitates which would be formed by water? As much
>>> as I would wish for life and water on mars I see nothing to convince me
>>> yet.
>>> Cheers
>>> Steve Dunklee
>>> --- On Thu, 5/30/13, Ron Baalke <baalke at zagami.jpl.nasa.gov> wrote:
>>>> From: Ron Baalke <baalke at zagami.jpl.nasa.gov>
>>>> Subject: [meteorite-list] Pebbly Rocks Testify to Old Streambed on Mars
>>>> (MSL)
>>>> To: "Meteorite Mailing List" <meteorite-list at meteoritecentral.com>
>>>> Date: Thursday, May 30, 2013, 7:01 PM
>>>> http://www.jpl.nasa.gov/news/news.php?release=2013-181
>>>> Pebbly Rocks Testify to Old Streambed on Mars
>>>> Jet Propulsion Laboratory
>>>> May 30, 2013
>>>> PASADENA, Calif. - Detailed analysis and review have borne
>>>> out
>>>> researchers' initial interpretation of pebble-containing
>>>> slabs that
>>>> NASA's Mars rover Curiosity investigated last year: They are
>>>> part of an
>>>> ancient streambed.
>>>> The rocks are the first ever found on Mars that contain
>>>> streambed
>>>> gravels. The sizes and shapes of the gravels embedded in
>>>> these
>>>> conglomerate rocks -- from the size of sand particles to the
>>>> size of
>>>> golf balls -- enabled researchers to calculate the depth and
>>>> speed of
>>>> the water that once flowed at this location.
>>>> "We completed more rigorous quantification of the outcrops
>>>> to
>>>> characterize the size distribution and roundness of the
>>>> pebbles and sand
>>>> that make up these conglomerates," said Rebecca Williams of
>>>> the
>>>> Planetary Science Institute, Tucson, Ariz., lead author of a
>>>> report
>>>> about them in the journal Science this week. "We ended up
>>>> with a
>>>> calculation in the same range as our initial estimate last
>>>> fall. At a
>>>> minimum, the stream was flowing at a speed equivalent to a
>>>> walking pace
>>>> -- a meter, or three feet, per second -- and it was
>>>> ankle-deep to
>>>> hip-deep."
>>>> Three pavement-like rocks examined with the telephoto
>>>> capability of
>>>> Curiosity's Mast Camera (Mastcam) during the rover's first
>>>> 40 days on
>>>> Mars are the basis for the new report. One, "Goulburn," is
>>>> immediately
>>>> adjacent to the rover's "Bradbury Landing" touchdown site.
>>>> The other
>>>> two, "Link" and "Hottah," are about 165 and 330 feet (50 and
>>>> 100 meters)
>>>> to the southeast. Researchers also used the rover's
>>>> laser-shooting
>>>> Chemistry and Camera (ChemCam) instrument to investigate the
>>>> Link rock.
>>>> "These conglomerates look amazingly like streambed deposits
>>>> on Earth,"
>>>> Williams said. "Most people are familiar with rounded river
>>>> pebbles.
>>>> Maybe you've picked up a smoothed, round rock to skip across
>>>> the water.
>>>> Seeing something so familiar on another world is exciting
>>>> and also
>>>> gratifying."
>>>> The larger pebbles are not distributed evenly in the
>>>> conglomerate rocks.
>>>> In Hottah, researchers detected alternating pebble-rich
>>>> layers and sand
>>>> layers. This is common in streambed deposits on Earth and
>>>> provides
>>>> additional evidence for stream flow on Mars. In addition,
>>>> many of the
>>>> pebbles are touching each other, a sign that they rolled
>>>> along the bed
>>>> of a stream.
>>>> "Our analysis of the amount of rounding of the pebbles
>>>> provided further
>>>> information," said Sanjeev Gupta of Imperial College,
>>>> London, a
>>>> co-author of the new report. "The rounding indicates
>>>> sustained flow. It
>>>> occurs as pebbles hit each other multiple times. This wasn't
>>>> a one-off
>>>> flow. It was sustained, certainly more than weeks or months,
>>>> though we
>>>> can't say exactly how long."
>>>> The stream carried the gravels at least a few miles, or
>>>> kilometers, the
>>>> researchers estimated.
>>>> The atmosphere of modern Mars is too thin to make a
>>>> sustained stream
>>>> flow of water possible, though the planet holds large
>>>> quantities of
>>>> water ice. Several types of evidence have indicated that
>>>> ancient Mars
>>>> had diverse environments with liquid water. However, none
>>>> but these
>>>> rocks found by Curiosity could provide the type of stream
>>>> flow
>>>> information published this week. Curiosity's images of
>>>> conglomerate
>>>> rocks indicate that atmospheric conditions at Gale Crater
>>>> once enabled
>>>> the flow of liquid water on the Martian surface.
>>>> During a two-year prime mission, researchers are using
>>>> Curiosity's 10
>>>> science instruments to assess the environmental history in
>>>> Gale Crater
>>>> on Mars, where the rover has found evidence of ancient
>>>> environmental
>>>> conditions favorable for microbial life.
>>>> More information about Curiosity is online at:
>>>> http://www.jpl.nasa.gov/msl , http://www.nasa.gov/msl and
>>>> http://mars.jpl.nasa.gov/msl/ .
>>>> You can follow the mission on Facebook at:
>>>> http://www.facebook.com/marscuriosity and
>>>> on Twitter at
>>>> http://www.twitter.com/marscuriosity .
>>>> Guy Webster 818-354-6278
>>>> Jet Propulsion Laboratory, Pasadena, Calif.
>>>> guy.webster at jpl.nasa.gov
>>>> 2013-181
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Received on Fri 31 May 2013 07:39:00 PM PDT

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