Red color in the edge of a shadow (APOD 21 Jun 2008)

[Karthik]

http://antwrp.gsfc.nasa.gov/apod/ap080621.html

The edge of the shadow of the left wall of the trench has a reddish tinge. I wonder what it is. The right wall shadow does not seem to have it.

Thanks

[Case]

The vanishing act likely demonstrates the sublimation of ice in the trench

If this is sublimation, does it have to be water ice, or are there other substances that could be a candidate?

[henk21cm]

The vanishing act likely demonstrates the sublimation of ice in the trench

If this is sublimation, does it have to be water ice, or are there other substances that could be a candidate?

Maybe CO2.



at 0.01 atm the sublimation temperature is -120 C. At Phoenix' landing site it is definitively warmer, so sublimation is no point. The question is rather 'could CO2 freeze at these temperatures and pressures'?

Nitrogen ice is white, but it takes cooling to 60K to freeze it. Methane is liquified at 120K, so solid methane is out of the question. Ammonia has a triple point at 195K and 0.6 atm pressure. Possible. I do not know its colour in the solid state, nor do i have a phase diagram.

[orin stepanek]

The vanishing act likely demonstrates the sublimation of ice in the trench

If this is sublimation, does it have to be water ice, or are there other substances that could be a candidate?

It could be dry ice [CO2]; but if I remember right, dry ice is more opaque. To me it looks like water ice. Guess we'll have to wait for test results from the scooper's oven.
Orin

[NoelC]

Are these color images made by a black and white camera imager in front of which colored filters are rotated?

If so, then the images are made of exposures taken at slightly different times, and the sun could have risen or set slightly between the exposures.

Under high magnification there is a hint of green along the colored edges of the shadow as well.

-Noel

[starnut]

How many thousands of feet above Earth's sea level would Mars' surface atmospheric pressure be equivalent to? Also, what is the average temperature at that altitude compared with the surface temperature at the Phoenix site?

Gary

[henk21cm]

How many thousands of feet above Earth's sea level would Mars' surface atmospheric pressure be equivalent to?

35 km. The average temperature at 35 km height baove the earth is about 230 K. (Page F168 handbook of chemistry and physics)

At Phoenix' landing site the daytime temperature is about 200K, nighttime 175K. (Nasa site?)

Split up the two images of the Vanishing act. Determined the horizontal and vertical shift between both and shifted one of them back. Then stored both images to disk. When you load these into a viewer and switch back and forward, a few things are visible.

1. In the shade, left bottom of the trench, some items disappear.
2. At the top of the trench the white area is getting darker.
3. Between the shade and the white area, along the right edge of the left trench (i can see three overlapping trenches) in the sunlit part something disappeared.
4. Along the right edge of the middle trench in the center of the pit something, a pebble sized item, has changed as well.
5. The slope of the trench at the bottom of the picture is stable. Minute changes in light intensity can be contributed to a different heigth of the sun.
6. The images are rotated slightly with respect to each other.
7. (Controversial)The dark region in the shade, bottom left, seems to have grown, after 4 days, like a stain on the ceiling, when your roof is leaking.

Item 1 is most intriguing. Like item 2, it might be a case of changing colour, getting darker. When i compare item 1 with item 2, what i see is only a slight darkening of the white area (item 2), whereas item 1 seems to be disappeared completely. By no means item 7 implies that water is leaking out of the soil, although the analogy is striking, an error due to the limitations of the human mind.

Question. How can i share these shifted images with you? I do not have an URL, since i do not have access to a website.

[Andy Wade]

Split up the two images of the Vanishing act. Determined the horizontal and vertical shift between both and shifted one of them back. Then stored both images to disk. When you load these into a viewer and switch back and forward, a few things are visible.

1. In the shade, left bottom of the trench, some items disappear.
2. At the top of the trench the white area is getting darker.
3. Between the shade and the white area, along the right edge of the left trench (i can see three overlapping trenches) in the sunlit part something disappeared.
4. Along the right edge of the middle trench in the center of the pit something, a pebble sized item, has changed as well.
5. The slope of the trench at the bottom of the picture is stable. Minute changes in light intensity can be contributed to a different heigth of the sun.
6. The images are rotated slightly with respect to each other.
7. (Controversial)The dark region in the shade, bottom left, seems to have grown, after 4 days, like a stain on the ceiling, when your roof is leaking.

Item 1 is most intriguing. Like item 2, it might be a case of changing colour, getting darker. When i compare item 1 with item 2, what i see is only a slight darkening of the white area (item 2), whereas item 1 seems to be disappeared completely. By no means item 7 implies that water is leaking out of the soil, although the analogy is striking, an error due to the limitations of the human mind.

Question. How can i share these shifted images with you? I do not have an URL, since i do not have access to a website.

Email them to me and I'll do it for you.
My email address is as follows:

me
at
andywade.co.uk

[Andy Wade]

OK, the two images are available for download here:

http://www.andywade.com/marsphoenix/s20.png

http://www.andywade.com/marsphoenix/s24.png

Save them to your harddrive and you can swap between the two in a suitable picture viewer on your own computer.

Or you can do it by opening one up, then pasting the second picture url in your browser address bar and press the back and forward buttons to swap images.
Either way it's pretty impressive, cheers Henk!

[golfnut1954]

When I saw the potentially historic pictures showing the particles in the soil assumed to be ice, I had a thought. Now, maybe this is redundant to what we already know of the Martian atmosphere. But, have we ever set out a small quantity of water, and observed the rate of evaporation?
Thanks,
Jeff W. Owens

[NoelC]

Here, I'll make it easy:

I did a fairly exact alignment of the two images, a very slight curves adjustment to get the exposure and color balance quite similar between the two frames, then animated the frames via a GIF file.

It becomes easy to see what's changed.

Notably, very, very little has changed in the undisturbed area at the top, where the scoop did not go. Things have reached a relatively stable state of rest up there. Where the scoop has been, and where things possibly fell out of it as it was brought up out of the ground, we see things change.



-Noel

[astrolabe]

Hello NoelC,

Thank you for your talent, it really is easier to see the matter clearer this way. It is also mesmerizing with it's implications!

[bluegreenheart]

Noel C,
You ARE the man.
You rock.
Thanks!

[apodman]

It becomes easy to see what's changed.

Nice gif. Reminds me of the old blink microscope that has contributed to so much discovery and research:

http://en.wikipedia.org/wiki/Blink_comparator

Also, since we've all taken up the pastime of melting and/or sublimating unknown substances on Mars, we've seen a few (solid - liquid - gas) chemical phase diagrams. I had to re-educate myself in some features of these diagrams, and went looking. For pure substances like water or CO2 (not mixtures), this link provides a good detailed review of every aspect of a phase diagram:

http://www.chemguide.co.uk/physical/pha ... diags.html

[BMAONE23]

Here is a good B/W "blink" comparison GIF between both images

from the Phoenix website

[Lucio]

in the middle right region of the trench i see like a imprint of a foot ! [/img]

[henk21cm]

OK, the two images are available for download here:

Thanks Andy, for providing shelter for my images. I must admit, the animated gif that qev shared with us, outclasses my efforts. I wonder, how did he do that?

[Andy Wade]

OK, the two images are available for download here:

Thanks Andy, for providing shelter for my images. I must admit, the animated gif that qev shared with us, outclasses my efforts. I wonder, how did he do that?

You're most welcome Henk.
I know, he's clever isn't he? I have a picture editing program that can do exactly that but never thought to try it.
Doh!
It just puts two pictures into one and you can set how many frames each image appears for, to extend the 'blink' length. Pretty straightforward really. Kind of like a very short 'movie'.

Anyway, the main thing is that we got there in the end.
It's amazing watching the blinking .gif and seeing things disappearing and reappearing.
I'm still not completely sure what I'm seeing but the idea of something frozen sublimating on exposure is very enlightening and for me it helps bring into focus just what an amazing thing they have done to even hit Mars, never mind landing and carrying out these detailed experiments.

And yes Lucio, that does look like a foot doesn't it? Complete with toes too!

[NoelC]

That was me, Henk, not qev.

Here's a rundown of what I did:

1. Open the two images from the NASA site in Adobe Photoshop CS2.

2. Paste the second image over the first.

3. Double the size in each dimension to help with more accurate positioning.

4. Set the opacity of the upper layer (second image) to 50% so that one sees a mixture of both images.

5. Use the "Free Transform" function to both position and rotate the upper layer so as to coincide with the first. The parts of the image that are fixed between the two become clear when near exact alignment is made.

6. Make the top layer 100% opaque.

7. Halve the size in each dimension.

8. Choose the Edit in ImageReady function.

9. In ImageReady, convert the layers to frames in the Animation palette.

10. Save Optimized, as a GIF file.

I used Photoshop CS2 instead of the newer CS3 because they have removed the Edit in ImageReady function (I think to the more expensive CS3 Extended version, which I do not have).

-Noel

[henk21cm]

That was me, Henk, not qev.

My excuses, NoelC, for that mix up. And thanks for informing me with the "How did you do that" info.

I followed a very basic approach.

1) Read two images

2) Made a correlation of both images in the frequency domain, by fast fourier transforms of the two red colourplanes. The technique is called "registring".

3) Shifted the first image according to the value as found by the correlation

4) Wrote both to disk

I use a program called Matlab to do the processing. It's a kind of computer language for data analysis, including images.