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Sol 90+, Extended mission
01101001
post Sep 24 2008, 02:08 PM
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QUOTE (MahFL @ Sep 24 2008, 06:22 AM) *
Can I just get confirmation from someone that the white stuff in this picture is CO2 frost ?
Thank you.


Is it cold enough yet?

New York Times: Who Cares if There’s Ice on Mars?

QUOTE
Even the low temperature of minus-122 [F] degrees is still too warm for freezing carbon dioxide in Mars' atmospheric conditions. But when winter returns, temperatures will drop, carbon dioxide will begin freezing out of the air again, and Phoenix will become entombed in dry ice.


Mars Weather Report: Sol 109 Minimum: -86C -122.8 F

Edit: Here's a source for a CO2 freezing point on Mars, NASA: Mars Polar Lander:

QUOTE
The composition of Mars' atmosphere results in a very unfamiliar seasonal effect. Carbon Dioxide, which makes up 99% of the air on Mars, turns to solid, or "dry ice", when it freezes at 148 ° Kelvin (-193 °F).
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Ant103
post Sep 24 2008, 03:05 PM
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QUOTE (MahFL @ Sep 24 2008, 03:22 PM) *
Can I just get confirmation from someone that the white stuff in this picture is CO2 frost ?
Thank you.

Frost ?


Yes, that's frost smile.gif


And in Snow White :



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Pertinax
post Sep 24 2008, 07:08 PM
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QUOTE (1101001 @ Sep 24 2008, 09:08 AM) *
Is it cold enough yet?

Mars Weather Report: Sol 109 Minimum: -86C -122.8 F


Two other things to keep in mind:

1) at what elevation is the -86C being measured at (either 0.25, 0.5, or 1.0m)
2) how much more does the surface of the ground cool relative even to the 0.25m temperature value due to radiational cooling?

Remember, even frost can form here on a still clear night on even with temperatures near 40F.

I am not arguing that that is CO2 frost (personally I think it's H2O), rather that I think we'll see CO2 frost before the met mast notes the CO2 frost point.


-- Pertinax
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3488
post Sep 24 2008, 07:16 PM
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Temps are @ 1 metre IIRC.

Also Oven 2 appears to have partially opened. Sol 118.

SSI as imaged by the RAC Sol 117.
Attached Image


Attached Image


The originals were very dark, so I have cropped, enlarged, brightened & contrast enhanced them.

Andrew Brown.


--------------------
"I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.
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01101001
post Sep 24 2008, 08:22 PM
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QUOTE (Pertinax @ Sep 24 2008, 12:08 PM) *
I am not arguing that that is CO2 frost (personally I think it's H2O), rather that I think we'll see CO2 frost before the met mast notes the CO2 frost point.


Maybe we'll see it. When it does happen it'll probably be hard to see, happening on top of a nice layer of water frost, which has a much higher freezing point.

Is the current difference between measured air temperature and ground likely to be the required circa 40 degrees C (air, minimum, maybe an average of the several mast sensor readings, recently: -86 C, freezing point: -125 C) for carbon dioxide frost? I don't think so.

It's still mid-calendar-summer for Phoenix. Autumn begins around our Christmas time. The cold is coming. The CO2 frost is coming too. But also conjunction is coming mid-November, and speculation by Barry Goldstein (I think) was that might be the last we hear from Phoenix.
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elakdawalla
post Sep 24 2008, 08:24 PM
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Goldstein said to me that the downward-trending power prediction graph intersected with the minimum-power level on a date that was, coincidentally, very close to the date of Mars solar conjunction. Keeping in mind that, as an engineer, it's his job to be a pessimist, he was pessimistic about Phoenix surviving beyond conjunction.

--Emily


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Stu
post Sep 24 2008, 08:32 PM
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Plenty of life left in our fiery bird yet... smile.gif

Sol 118 colourisation... nice chunka frost on the right there... local time 17.30...

Attached Image


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peter59
post Sep 24 2008, 08:44 PM
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Next dust devil near Phoenix - sol 117.
Attached Image


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JRehling
post Sep 24 2008, 08:50 PM
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The ground will have a much greater thermal inertial than the skinny solar panels, so it seems to me that they could become foci of frost formation long before the ground would be cold for enough of the cycle to allow massive depositions. This is the "bridges may be icy" effect. A bridge is cooled by the air on all sides, above and below. The ground is only cooled from above. A "wave of cold" can penetrate to the center of mass of the bridge or solar panel, but can never do that with the planet below.

In both cases, there should be a runaway effect, because the dark panels and dark ground will suddenly absorb much less heat when frost covers them. (Relevant if the sun is still adding any heat at all.) That could cause the fraction of sunlight absorbed to plummet from 80-90% down to 10%. Those solar panels will quickly win or tie the contest for the coldest surfaces around.

It's hard to say if the frost would build up on them faster than the ground layer would grow up to them. Obviously, it's a function of their height. My guess is it will build up on them first. IIRC, the whole seasonal layer is only about 2 m thick. Maybe we'll see some springtime pictures of panels lying next to the lander. If they do break off, they could become, in springtime, the foci of interesting melting effects. Maybe they could even drift horizontally as the base of ice sublimates.
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Phil Stooke
post Sep 24 2008, 09:22 PM
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Ah yes, 'bridges may be icy'. It always surprises me to see that sign at the corner of Space Center and NASA Boulevard (NASA Road 1) adjacent to JSC. How often is it icy there?

If the panels were lying next to the lander it could be a bit difficult to power up the camera to photograph them.

Phil


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Vultur
post Sep 25 2008, 01:25 AM
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QUOTE (Phil Stooke @ Sep 24 2008, 09:22 PM) *
Ah yes, 'bridges may be icy'. It always surprises me to see that sign at the corner of Space Center and NASA Boulevard (NASA Road 1) adjacent to JSC. How often is it icy there?


Never, or close enough.
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Aussie
post Sep 25 2008, 10:36 PM
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What is the temperature gradient profile from the ground up? I would have anticipated that CO2 would freeze out and fall as 'snow' in which case it will collect on the upper areas of Phoenix and the area immediately below the solar panels/body would have minimal buildup of CO2 ice. The solar panels wouldn't hold out for long in that scenario. But I am outside my comfort zone here and the atmospheric freeze scenario is too alien for me to get my mind around. What would be the likely ground level wind movement at the Phoenix site when the freeze starts? Lots of horizontal movement of ice crystals or more of a vertical deposition?
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marsophile
post Sep 25 2008, 11:46 PM
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If there is some slack in the wires connecting the solar panels to the spacecraft, then maybe the panels can break off and fall to the ground, but still function again when the Spring thaw comes? wink.gif

Perhaps the robot arm could even pile some dirt under the panels to help support them so they won't break off, if they are not too high above the ground...
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PDP8E
post Sep 26 2008, 07:20 PM
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I downloaded a little 'gif animator' (I wont tell you which one, you will just have to slueth it out rolleyes.gif )

Here are some clouds going by Phoenix as she looked for dust devils

Attached Image






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john_s
post Sep 26 2008, 09:25 PM
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That's a seriously cloudy sky. I wonder what it's doing to the solar power levels?

John.
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