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

From: Pict <pict_at_meteoritecentral.com>
Date: Sat, 01 Jun 2013 18:59:39 +0200
Message-ID: <CDCFEE74.18A4A%pict_at_pict.co.uk>

Aeolian desert sands can exhibit remarkable sphericity, rounding and
sorting not unlike extremely mature water worn clastic sediments, but I
don't think the phenomena extends to grain sizes beyond a few millimetres.
It does seem conceivable that very high wind speeds with a denser
atmosphere might get tumbling agitation going with larger rocks, but
poorly sorted conglomerates suggests water not wind from an earthly
perspective.
John

On 01/06/2013 23:55, "Graham Ensor" <graham.ensor at gmail.com> wrote:

>Yes, Steve, Larry....erosion, if the flowing CO2 could produce any,
>would not be anything like flowing water...eg tumbling rock into round
>pebbles..the best you could hope for would be some sorts of ventifacts
>being created...just as flowing gases (wind) create on earth.
>
>Graham
>
>On Sat, Jun 1, 2013 at 1:14 PM, <lebofsky at lpl.arizona.edu> wrote:
>> Hi Steve:
>>
>> Yes, I did see your video link. Thanks for sending that. All that this
>> demonstrates is that CO2 is denser than air and that, when it displaces
>> the oxygen, the candle goes out. So, even in this case it is not the
>>force
>> of the CO2 that is putting the flame out, but the lack of oxygen.
>>
>> CO2 gas is 1.5 as dense as air, but 1/500 the density of water. I doubt
>> that you could mimic the know effects of moving water in a stream bed
>>with
>> a much less dense gas. If nothing else, the gas would disperse in the
>> atmosphere rapidly unlike the much denser water.
>>
>> Sublimation is a very slow process, look at comet nuclei. There is a
>>limit
>> to how fast something can sublimate. As the ice warms up and turns to
>>gas,
>> the energy needed to do this actually cools the surface (the same thing
>>as
>> evaporative cooling which cools you as sweat evaporates off of your
>>skin).
>> I wrote several papers years ago on ice sublimation.
>>
>> The scientists used the sizes and size distribution of the rounded
>>grains
>> to compare with what we see in stream beds on Earth and can actually
>>come
>> up with depth, duration, and speed of the water. I do not see how you
>> could replicate that with a gentle flow of gas no matter how long you
>>had.
>>
>> Your idea is interesting, but decades of research have shown that
>>geologic
>> processes on Mars (and other objects) are not that different than what
>>we
>> see on Earth. If we see on Mars what looks like a stream bed on Earth,
>>it
>> is likely that the process that formed the stream bed on Earth (water)
>> also did this on Mars. So, what conditions would have been necessary for
>> the stream bed to have formed on Mars? A little more atmosphere and a
>> little warmer!
>>
>> I hope that this helps.
>>
>> Larry
>>
>>
>>
>>
>>> I believe I did not describe properly what I was trying to say. The
>>>video
>>> link I sent clearly showed co2 gas being poured from a beaker. During
>>>the
>>> cold mars night a thin layer of co2 frost can form on a hillside. when
>>> daylight returns and thaws the frost, the recently sublimated co2 being
>>> colder than the surrounding atmosphere is going to flow down hill.
>>> Millions of years of colder denser gas flowing down hill is going to
>>>cause
>>> erosion that simulates the flow of water.
>>> Mars has an 100 thousand year polar freeze thaw cycle. When
>>>billions
>>> of tons of co2 sublimate from the poles its going to flow out from the
>>> poles and cause erosion as it does so. Millions of years of this
>>> repeated cycle of the colder gas flowing down hill is going to carve
>>> what looks like river beds, canyons and lakes. all without any water
>>> needed.
>>> Cheers
>>> Steve
>>>
>>> --- On Fri, 5/31/13, Graham Ensor <graham.ensor at gmail.com> wrote:
>>>
>>>> From: Graham Ensor <graham.ensor at gmail.com>
>>>> Subject: Re: [meteorite-list] Pebbly Rocks Testify to Old Streambed on
>>>> Mars (MSL)
>>>> To: lebofsky at lpl.arizona.edu
>>>> Cc: "Steve Dunklee" <steve.dunklee at yahoo.com>, "Meteorite Mailing
>>>>List"
>>>> <meteorite-list at meteoritecentral.com>, "Ron Baalke"
>>>> <baalke at zagami.jpl.nasa.gov>
>>>> Date: Friday, May 31, 2013, 11:39 PM
>>>> 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.
>>>>
>>>> G
>>>>
>>>> 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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>>>> >
>>>> >
>>>>
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Received on Sat 01 Jun 2013 12:59:39 PM PDT