Starship Asterisk*

White Rock Fingers on Mars

Explanation: What caused this unusual light rock formation on Mars? Intrigued by the possibility that they could be salt deposits left over as an ancient lakebed dried-up, detailed studies of these fingers now indicate a more mundane possibility: volcanic ash. Studying the exact color of the formation indicated the possible volcanic origin. The light material appears to have eroded away from surrounding area, indicating a very low-density substance. The stark contrast between the rocks and the surrounding sand is compounded by the unusual darkness of the sand. The above picture was taken with the Thermal Emission Imaging System on the Mars Odyssey spacecraft currently orbiting Mars. The image spans about 10 kilometers inside a larger crater.

<< Previous APOD

Discuss Any APOD

Next APOD >>

[/b]

Good lead-in for tomorrow's spooky sky. Too bad they aren't folsilized bones. That would be an even better lead-in. And also something that you would be glad is on mars and NOT earth!

My compliments to Emily Lakdawalla for providing such a clear and understandable explanation of the White Rock images (APOD April 7, 2008). Her non-technical discussion is a welcome relief.

They have found the Abominable Snowman!!!

(Chris, you sure that isn't you?)

Ann

That last link was really something with the formation inside the crater.

Surely if this image was created using thermal imaging, the various tones correspond to the temperature of the different materials, and not 'light and dark' in repect to the visible spectrum. Or is the correspondence between tone and temperature always very close with lithic materials?

Curious
Michael

Good Halloween choice!

orin stepanek wrote:That last link was really something with the formation inside the crater.

Click to view full size image

What is it about Mars that so many of the images come out looking "inside-out" (meaning that things that should look like indentations seem to be easily misinterpreted as extrusions)?

-Noel

NoelC wrote:What is it about Mars that so many of the images come out looking "inside-out" (meaning that things that should look like indentations seem to be easily misinterpreted as extrusions)?

It's just that old crater-and-hill illusion, the product of our lighting expectations. The thing with these Mars images is that there is lots of topographic structure, and for the most part, no attempt to orient the images so that the lighting direction is "normal". And of course, there is usually nothing else in the images to provide other cues for our perception.

Hell, as any self-respecting genius in Ancient Aliens or UFO watchers knows those tracks are Mars Dino-tracks, of course. Its another NASA conspiracy. [Like my spelling?]...LMAO waiting for the conspiracy books to begin to breed. BTW...great picture...science beats ignorance forever!

Chris Peterson wrote:no attempt to orient the images so that the lighting direction is "normal"

You'd think the "normal" lighting direction would be from above, so why do I see your first image as bumps and the second as divots when I first look at it? Is my brain just upside-down? In all seriousness, the other day I had a DEVIL of a time seeing those dry ice pits on mars as anything but raised plateus.

-Noel

Chris Peterson wrote:

Optical00251.png

Optical00261.png

Chris, you have the coolest Legos!

NoelC wrote:

Chris Peterson wrote:no attempt to orient the images so that the lighting direction is "normal"

You'd think the "normal" lighting direction would be from above, so why do I see your first image as bumps and the second as divots when I first look at it? Is my brain just upside-down? In all seriousness, the other day I had a DEVIL of a time seeing those dry ice pits on mars as anything but raised plateus.

-Noel

I see the first ones as divots and the second one as bumps.

Image of Mars Odyssey spacecraft.
I think that this material has a volcan origin for the low-density and white color light.
A rover "saw" a rock look like this image,too.

Obviously, this is Mars' bony , outstretched hand, Trick-or-Treating at Earth's door. Happy Hallowe'en y'all

Beyond wrote:

NoelC wrote:

Chris Peterson wrote:no attempt to orient the images so that the lighting direction is "normal"

You'd think the "normal" lighting direction would be from above, so why do I see your first image as bumps and the second as divots when I first look at it? Is my brain just upside-down? In all seriousness, the other day I had a DEVIL of a time seeing those dry ice pits on mars as anything but raised plateus.

-Noel

I see the first ones as divots and the second one as bumps.

Copy either image to your computer and rotate it 180 (turn upside down). It will then look just like the other image. (Or, stand on your head to view it if you prefer.) Best I can figure, we are just accustomed to seeing things usually lit from above. In that regard, “normal” is nothing more than “customary”.

Ann wrote:They have found the Abominable Snowman!!!

(Chris, you sure that isn't you?)

Ann

Not YET I think.

MGTS24 wrote:Surely if this image was created using thermal imaging, the various tones correspond to the temperature of the different materials, and not 'light and dark' in repect to the visible spectrum. Or is the correspondence between tone and temperature always very close with lithic materials?

Curious
Michael

Your understanding is a little off, although to be fair, most people don't realize that "infrared" is a very, very broad description of a type of light that can be interpreted to include anything with a longer wavelength than red (infra = beyond...beyond red), although it's usually considered more limited than that.

Measuring in nanometers (nm = billionths of a meter), the deepest red a human can perceive is around 750-790 nm (can vary person-to-person).

Beyond that, is the so called near-infrared (790 nm to 1400 nm) band. Our eyes aren't sensitive electromagnetic radiation at these wavelengths, but generally, it behaves very similar to visible light (reflects off most objects...only very hot objects radiate these wavelengths...things that are just barely not hot enough to visibly glow).

There's two bands of mid-infrared - from 1400nm to 3000nm, to which the atmosphere is opaque, because water vapor in the atmosphere acts absorbs them, acting like a smoke screen to these wavelengths, and from 3000nm to 8000nm. This latter band is getting into what the type of infrared you're thinking of known as thermal infrared - where objects are visible based on their radiation of heat, but typically only if they're hotter than room temperature.

Finally you have thermal infrared, from 8,000nm to 15,000nm (above 15,000nm, most electromagnetic radiation is again absorbed by water vapor until you get down to the microwave radio wavelengths), or about 10-20 times the wavelength of visible light. Objects at room temperature radiate strongly enough in the thermal infrared spectrum to be detectable.

Anyways, although the name of the camera is the "Thermal EMission Imaging System" (THEMIS), it actually has the ability to detect light from all of the above bands, including visible light.

The image from this APOD was taken in a visible or near visible wavelength, so it is reflections of incoming visible or infrared light, just like taking a picture with a camera.

However, your original premise is correct - if this really were an image of emitted thermal radiation, the brightness would be heavily affected by temperature.