Please note, English is not my native language.


* "Chosp" schriebt:

"Alf P. Steinbach" wrote in message
...

url: http://home.no.net/dubjai/misc/moc/M0902042.jpg [ca. 836 kiB]


This is, as I understand it, near the south pole of Mars.

At the very bottom there are some features which to my untrained eye look
very much like lakes, which I have cropped out of the main photo and
placed here (just 19 kiB):


A: url: http://home.no.net/dubjai/misc/moc/nederste_av_M0902042.jpg


What you are looking at is an optical illusion. If you view the crater
about midway down the image, you will notice that, without doubt, the light
is coming up the the bottom or the image. Therefore what you took to be lakes
are not depressions at all - but are mesas which stick up above the
surroundings.

Thank you for that insight. The photo does look entirely different when
rotated 180 degrees. Truly amazing!

But exactly what is a "mesa" that sticks up above the surroundings?

Google and Hyperdictionary insists a mesa is a depression, a basin.

And these particular mesas, if that's what they are, seem to be
incredibly smooth on top, and have very strange droplet-like boundaries.

Before posting to sci.astro.research and later to sci.astro I checked the
feature photos of Mars, including many "mesa" photos (e.g. heart-shaped)
shown in url: http://www.msss.com/mars_images/moc/themes/MESAS.html, but
none looked like this -- all other mesas seem to (1) be depressions with
(2) non-smooth interior and (3) ordinary-looking boundaries?




This is a common mistake made when the lighting is contrary to our
usual expectations (i.e. coming from the top of the image). If you invert
the image it may be more readable to you.

I wonder what this is -- I received no reply at all when mailing the
public "astronomy question" address at the University of Oslo.

Also, but less interesting, I wonder if the features that look like ice
roses (hundreds of meters wide), e.g. at the very top of that photo,


B: url: http://home.no.net/dubjai/misc/moc/oeverste_av_M0902042.jpg.

Another illusion. The "ice roses" appear to stick out of the ground - when
actually they are depressions. Check the lighting on the crater.
You'll see.
As to what they actually are, that is a mystery to me.

Uh huh... Mystery. But thanks anyway.



Also -- this is one heck of feature-rich photo! ;-) -- I wonder about
the seemingly rectangular kilometer-wide depression or crater (whatever)
in the middle of the picture,


C: url: http://home.no.net/dubjai/misc/moc/midterste_av_M0902042.jpg


But, first and foremost, does anyone know about the looks-like-lakes at
the
bottom, in (A)? In addition to those at the very bottom there's a smaller
one
a little bit upward from the bottom. The smooth gray-color gradients in
the
interiors of the features might be shadow, but it doesn't look that way.

Again, they are mesas. They stick up above the surface, not below it.
Use the crater as a lighting reference. If they were lakes - the craters
would have to be domes.

So (C) is a kind of rectangular kilometerwide "mesa" that like (A) sticks
up above the surroundings, but unlike (A) has ordinary-looking boundaries
and a sort of corrugated interior instead of (A)'s very smooth interior?