Starship Asterisk*

I feel sorry, but I ca'nt recognize dunes. This pictures looks like an engine drive, I might be wrong, may be a different angel of view might help. or just some kind of scale?

makc, thank you for your effort to help us understand what we're looking at in the apod for 5 August, but even after looking at your view, I agree with Kuno that it's not clear what we're seeing. Perhaps a 3-D view would help. Regardless, it's quite beautiful!

Today's LPOD August 7, 2007, Yardings has some interesting information about dunes, patterned terrain and vegetation mounds from the link on the LPOD page yardings
Fascinating!

If we can accept for a moment that they ARE dunes, or something like that, and concentrate on the dots?
The "Sandy jets exploding" link takes us to a last years' APOD, that suggests that the jets raising layers of "interspersed dark sand would explain the color of the spots". That begs the question of there being a layer or layers of dark material in the dunes.

Earth dunes are uniform, no layers or even much differentiation of grain size with depth, as they are constantly and literally turning over, as they advance. If Martian dunes are layered, they have a different mechanism of formation.

And when dots occur on the edge of a face slope - the advancing edge of a dune on Earth - the dark material slides down it, like..... well, like water....whereas a jet would show a different pattern. And tthe dark material expands to cover the area as summer approaches. Is it possible? Growth?

Just puzzled and not enlightened by these pics and the APOD commentary.

John

John,

I'm not positive but It seems to me that the APOD referenced by the "sandy jets" link is referring to dark sand interspersed with CO2 rather than dark sand interspersed with light sand. Or, put another way, the jets are venting CO2 and the CO2 carries sand along with it.

Floyd,
So, there is CO2 snow, over dark sand. That I can believe.
As the summer approaches, and the planet warms, the CO2 below the surface is so warm that it sublimes, forms pockets of gas (?) and then EXPLODES like multiple geysers, all over the dune surface?
This brings dark sand to the surface, that absorbs more heat, that is transmitted deep into the CO2 where more is sublimed .... and so on.

Apart from not explaining why so much sand is lifted by these geysers of gas - geysers on earth are lifted by superheated water that explodes into steam and lifts water above it - this would require vast amounts of CO2 snow UNDER the sand. And a mechanism for transferring heat deep into the CO2 layer, without being depleted by vapourising CO2 snow.
Ever tried to boil an ice cube?

Sorry, I'm as convinced about this as I am about vast black Martian bacteria colonies.

John