Rounded Rocks in Gusev Crater

Marvin wrote:

Dick Morris wrote in
:

We have a lot of rocks here in Washington State, and such smooth,
rounded surfaces I've seen only on river rocks. Ditto for all the
rocks I've seen down in the deserts of Utah and Arizona.

You have an easy way of identifying earth rocks that have been exposed to
the surface for 2billion+ years? wow!

Get a clue please.. The earth surface is *active*. There are frequent(by
geological scales) glaciers marching past, lots of airborne stuff (dust,
sand, *rain*, *ice* , birds!, oxygen) that simply are not found in the same
form on Mars. Extrapolating your backyard-commonsense observations *will*
*not* *work* in an inherently foreign environment like Mars.

Take a few deep breaths and settle down. We don't know how long those
rocks have been exposed, and if you have some examples of smooth,
rounded rock surfaces that have indisputably been produced by wind
erosion I would like to see them.

In , on 01/08/04
at 08:02 PM, Marvin said:

Dick Morris wrote in
:

We have a lot of rocks here in Washington State, and such smooth,
rounded surfaces I've seen only on river rocks. Ditto for all the
rocks I've seen down in the deserts of Utah and Arizona.

You have an easy way of identifying earth rocks that have been exposed to
the surface for 2billion+ years? wow!

Get a clue please.. The earth surface is *active*. There are frequent(by
geological scales) glaciers marching past, lots of airborne stuff (dust,
sand, *rain*, *ice* , birds!, oxygen) that simply are not found in the
same form on Mars. Extrapolating your backyard-commonsense observations
*will* *not* *work* in an inherently foreign environment like Mars.

Neither will the assumption that all or even most of the rocks you see on
the surface of Mars today have been sitting on or even near the surface
for 2 Ga. That sort of assumption doesn't even work on the moon, which is
far less active than the surface of Mars. Just look over to "sleepy
hollow" to find a candidate for excavation. The only way we'll rigorously
know the surface age of Mars rocks is to look at the cosmic ray exposure
ages (some short lived isotopes, some stables produced by spallation
reactions). That will take a sample return mission, I'm afraid (for good
field control). Having said all that, they DO look like water rounded
rocks, don't they?

--
Chris M. Hall, Associate Research Scientist
Dept. of Geological Sciences, University of Michigan

Specialization is for insects

Chris Hall wrote:

In , on 01/08/04
at 08:02 PM, Marvin said:

Dick Morris wrote in
:

We have a lot of rocks here in Washington State, and such smooth,
rounded surfaces I've seen only on river rocks. Ditto for all the
rocks I've seen down in the deserts of Utah and Arizona.

You have an easy way of identifying earth rocks that have been exposed to
the surface for 2billion+ years? wow!

Get a clue please.. The earth surface is *active*. There are frequent(by
geological scales) glaciers marching past, lots of airborne stuff (dust,
sand, *rain*, *ice* , birds!, oxygen) that simply are not found in the
same form on Mars. Extrapolating your backyard-commonsense observations
*will* *not* *work* in an inherently foreign environment like Mars.

Neither will the assumption that all or even most of the rocks you see on
the surface of Mars today have been sitting on or even near the surface
for 2 Ga. That sort of assumption doesn't even work on the moon, which is
far less active than the surface of Mars. Just look over to "sleepy
hollow" to find a candidate for excavation. The only way we'll rigorously
know the surface age of Mars rocks is to look at the cosmic ray exposure
ages (some short lived isotopes, some stables produced by spallation
reactions). That will take a sample return mission, I'm afraid (for good
field control). Having said all that, they DO look like water rounded
rocks, don't they?

I've seen an awful lot of rocks like that in river beds and alluvial
deposits. (On my last vacation I spent 11 days backpacking in
Yellowstone NP. I forded the Snake River 8 times, the Thorofare 5
times, and the upper Yellowstone twice. I am quite familiar with the
appearance of river rocks.;-) Sometimes the obvious answer is the
correct one.

(Geology was one of my early interests, though I ended up as a EE. I
still have a tendency to come back from vacations with 50 pounds of
interesting rocks in the trunk of my car.)
--
Chris M. Hall, Associate Research Scientist
Dept. of Geological Sciences, University of Michigan

Specialization is for insects

"Blurrt" writes:

Just looking at the rocks on the floor of Gusev crater - they are rounded.
This implies water (or some other fluid) erosion.

Not neccessarily. Dust blowing over it for a few million years may have
quite similar effects. BTW mistaking the effects of winds and dust for
effects of water seems to be all too easy when dealing with features on
Mars.

I think from that first colour photo it is proven that Gusev indeed held
running water.

*If* there was water once, nothing that was in direct contact with it
will be found on the surface. The mission planers are expecting to look
at debris from (later) impacts, which may have digged deep enough to
shatter sediments from below over the surface.


Jochem

--
"A designer knows he has arrived at perfection not when there is no
longer anything to add, but when there is no longer anything to take
away." - Antoine de Saint-Exupery

January 6, 2003

Jochem Huhmann wrote:

*If* there was water once,

Oh great, yet another Mars water denialist.

Thomas Lee Elifritz
http://elifritz.members.atlantic.net/mars.htm

In article , Blurrt wrote:
Just looking at the rocks on the floor of Gusev crater - they are rounded.
This implies water (or some other fluid) erosion.

This is Mars, a gentle planet-sized sandblaster...

I think from that first colour photo it is proven that Gusev indeed held
running water.

I wouldn't say it immediately looks that way to me.

--
-Andrew Gray

Andrew Gray wrote:

In article , Blurrt wrote:

Just looking at the rocks on the floor of Gusev crater - they are rounded.
This implies water (or some other fluid) erosion.


This is Mars, a gentle planet-sized sandblaster...


I think from that first colour photo it is proven that Gusev indeed held
running water.


I wouldn't say it immediately looks that way to me.


I does kind of *look* like that, but looking at it really isn't
definitive or compelling. Besides, I though Gusev was a lake, and it
takes running water to round off rocks like that. The wind, over
probably 4-ish billion years, could easily cause the same effect.

Brett

In m,
Brett Buck spewed:
Andrew Gray wrote:

In article , Blurrt
wrote:

Just looking at the rocks on the floor of Gusev crater - they are
rounded. This implies water (or some other fluid) erosion.


This is Mars, a gentle planet-sized sandblaster...


I think from that first colour photo it is proven that Gusev indeed
held running water.


I wouldn't say it immediately looks that way to me.


I does kind of *look* like that, but looking at it really isn't
definitive or compelling. Besides, I though Gusev was a lake, and it
takes running water to round off rocks like that. The wind, over
probably 4-ish billion years, could easily cause the same effect.

Brett

I'm pretty sure I'm talking out of my ass here, but here's my question. Is
the Reynolds number for Martian atmospheric flow (wind) in any way
comparable to Earth-normal water flow?

I'm pretty sure I'm talking out of my ass here, but here's my question.
Is
the Reynolds number for Martian atmospheric flow (wind) in any way
comparable to Earth-normal water flow?


It is a fairly straitforward process calculating the Reynolds number, but
what comes after isn't. There you have to make a lot of assumptions and to
worsen things you can't compare with water that easily since Co2 gas is a
compresible fluid and water is incomressible (or nearly).
If you however want to work out the friction factor of the Martian wind I
might have some ideas on how to takle the problem. Start with a turbilent
flow across a flat plate (assuming turbular flow is save since we can
calculate the Reynolds number and see it's large). Asume the wind is an
ideal gas (not true, but if we haven't got any better data we have to use
this). Finally assume a zero pressure gradient. That will allow you to use
equations for turbular pipe flow, which are better understood and apply very
well in this case. An empirical power-law velocity provile with an exponent
of 1/7 is typically used.

Now for the reynolds number:
Re=U*L/nu=U*L*rho/mu (since nu = mu/rho)

where
U = stream velocity [m/s]
L = characteristic length of the flow geometry (i.e. distance from tube
entrance or hydraulic diameter for tubes) [m]
nu = kinematic viscosity [m^2/s]
mu = viscosty [kg/(s*m)]
rho = density [kg/m^3]

so for water at say 283 K at atmospheric pressu
Re = U*L/1.304E-6

And let's say the water speed is (related to the wind speeds):
U1 = 10 m/s (5 beaufort)
U2 = 20 m/s (8 beaufort)
U3 = 30 m/s (11 beaufort)

I don't know what real martian values for the wind speed are so I gave a
few.
We get:
Re1 = 7.7E6*L
Re2 = 1.5E7*L
Re3 = 2.3E7*L

Now it largely depends on the characteristic lengths, but we can say that
for L4mm (for these water speeds) the flow must be turbulent since
Re2.5E3 : Laminar flow
Re4E3 : Turbulent Flow

now I'll look at Mars once again starting with the equation for the Reynolds
number:
Re=U*L/nu=U*L*rho/mu (since nu = mu/rho)

We don't know the viscosity and density (or kinematic viscosity) so we have
to calculate it. Without giving the exact way of calculating it, you can
calculate the (absolute/dynamical) viscosity of a 100% carbon dioxide fluid
using the emirical Sutherland correlation and arive at 1E-5 kg/(s*m). This
not perfect for these low pressures but comes close.

To get a density we have to assume an ideal gas (not true). The equation of
state:
p = rho*R*T
and
R = Ru/Mm

where
T = temperature [K]
p = pressure [N/m^2]
Ru = universal gas constant = 8314 N*m/(kmol*K)
Mu = molecular mass

so:

Re = U*L*p*Mm/(Ru*T*nu)
Re = U*L*1E3*44/(8314*283*1E-5)
Re = U*L*1870

For the same speeds we get
Re = 1.87E4*L @ U=10 m/s
Re = 3.74E4*L @ U=20 m/s
Re = 5.61E4*L @ U=30 m/s

So there's a big difference between water and wind on mars..

Olaf