My guess is they show dirt.

I think they are clouds.

Images taken during the local dust storm that cleaned Spirit's panels back on sol 420 looked similar:
http://marsrovers.jpl.nasa.gov/gallery/all...8P1584L0M1.HTML

I had been watching the Themis site for updates of their 9 micron atmospheric opacity maps, hoping to see signs of the dust storm's end. When I tried to compare their optical depth opacity scale to the tau values we commonly refer to, I realized that the Themis instrument apparently pegs out at approximately a tau of 0.9.

It is probably not fair to strictly compare MER tau measurements to the 9 micron Themis maps, but we probably will not see prettier Themis maps with less red until tau drops below 1.
[attachment=11498:attachment]

I'd say dirt. Given that these sky images get a particularly heavy ammount of abuse when stretched to become the JPG's we see, I doubt that a calibrated image would show even 1% of the diversity of brightness that these JPG's show.

Doug

Looks like Oppy has been moving its her IDD:

http://marsrovers.jpl.nasa.gov/gallery/all...W0P1159R0M1.JPG

Check out the thick dust coating. Thank goodness the MI has a dust cover...

... and it looks like he/she/it will be moving again on sol 1271 for the first time since sol 1232!
That's how I read the imaging plan for tosol.

What have we done, it used to be so simple!!!

Rocker, where did you find out how to convert the themis opacity to a tau value? Is that from their sentence "The scale bar's values run from nearly clear (0.05) to roughly a one-third reduction in sunlight (0.40)"? A one third reduction in direct sun gives tau = 1.1, although they say "roughly". As you say, who knows how well 9 microns relates to visible, where Oppy get's most of her power.

Also, I don't get your plot - as I understand it tau = optical depth. What are your dots?

Edit: I see, your horizontal axis is the fraction of direct sun that makes it to the ground. Technically that shouldn't be called optical depth.

The individual sol tau's have been removed from Lemmon's site, and replaced with an updated plot with Oppy, Spirit, and Viking.

Gods, what a monster downpour! not to mention the panels!

...thought early on in the storm they might move Oppy close to the edge to take advantage of any turbulence that could be had by the terrain interface, but it looks like we're remaining at the back of the porch pretty much out of the wind (if there were any). but someone has probably already commented on that (yes, ive been out for a while). anyone know what the wattage is looking like now?

Wow...look at the tire tracks! What goes up certainly must come down...but not here!

Something like slightly less than low-to-mid-two-hundred, give or take a few here and there and add some...

You're right, fredk. I've corrected that in my post. I wanted to try to compare tau to the 9 micron opacity, but when I read an article to learn how to calculate tau from the ratio of sunlight intensities, I guess I got my terminology confused.

Now that I look back on it, I think the Themis site's description ("roughly a one-third reduction in sunlight (0.40)") is good. At tau = 0.40, e^-t = .67.

Just remember, from the best HiRISE images we have of them, neither of the Viking landers was significantly dust-covered prior to this storm.

And they've been through 31 years of Martian weather.

I think the rovers will be relatively clean again. Whether that happens in time for the batteries to remain fully operational, I can't say...

-the other Doug

They should get some nice panoramic pictures. It must look like freshly fallen snow there, albeit a thin layer of it.