Would like identification of some lake-like features in MGS photo of Mars

[
This q was posted in sci.astro.research about a week ago, and before
that in Norwegian newsgroups and public questions University of Oslo,
but _no response_ at all: apparently no-one knows or has any idea.
]


I stumbled over this Mars Global Surveyor photo,


url: http://www.msss.com/moc_gallery/m07_m12/images/M09/M0902042.html


"MOC narrow-angle image M09-02042", which covers an approx 2.8 km wide and
171.3 km high strip if I understand it correctly.

I have copied the photo he


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


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.


are formations due to freezing and thawing, or something else?

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.

TIA.,

- Alf

"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.
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.


are formations due to freezing and thawing, or something else?

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.

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?

In message , Alf P. Steinbach
writes

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.

Your dictionaries are mistaken :-)
"Mesa" isn't English - it's the Spanish for "table" and means just that
- a flat-topped "table land" of the sort you find all over the US
South-West and, judging by the pictures my brother just sent me, parts
of Arabia which look as dry and uninviting as Mars.
--
Save the Hubble Space Telescope!
Remove spam and invalid from address to reply.

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

Please note, English is not my native language.

I understand. I will try to be clear.

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

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

The word " mesa" , which means " table " in Spanish, is
defined (in a geological context) as an isolated, relatively
flat-topped natural elevation - usually more extensive than
a "butte" and less extensive than a "plateau".

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

I don't know what to say about that except that I've never seen
the word "mesa" used in any context to refer to a depression.
For what it's worth, I live on a mesa. I drive uphill to go home
and downhill to leave.

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

Mars Global Surveyor imagery has revealed that there are a
great many extremely flat mesas on Mars. The shadowy
appearence around the rims could be caused by several things
(such as wind-induced dust build-up or removal; uneven sublimation
of ices or frosts, etc.) and does not necessarily represent a
curvature of the edge. The image is indeed filled with optical
illusions.

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?

Your description looks about right.

In article ,
Alf P. Steinbach wrote:
But exactly what is a "mesa" that sticks up above the surroundings?

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

Note that Merriam Webster defines mesa as:

: an isolated relatively flat-topped natural elevation
usually more extensive than a butte and less extensive than
a plateau; also : a broad terrace with an abrupt slope on
one side

In message , Kenneth Chiu
writes
In article ,
Alf P. Steinbach wrote:
But exactly what is a "mesa" that sticks up above the surroundings?

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

Note that Merriam Webster defines mesa as:

: an isolated relatively flat-topped natural elevation
usually more extensive than a butte and less extensive than
a plateau;

That definition seems designed to provoke arguments :-)
Is it a butte if it's a square kilometre; is it a plateau if it's a
hundred square kilometres, and so on.
--
Save the Hubble Space Telescope!
Remove spam and invalid from address to reply.

* (Alf P. Steinbach) schriebt:

* "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!


For those who'd like to see the amazing transformation directly I've put the
original and rotated version, plus close up of a feature + rotation, at


url: http://home.no.net/dubjai/misc/in_or_out/


Enjoy.

With the close-up it's more clear that these features are not lakes, no
matter what tricks the light plays.