The folks at HiRISE have released another interesting and beautiful (false color) image of Mars. This time it’s a crater that has, of all things, terraced walls. This may indicate that ice under the surface was vaporized upon impact, then condensed and rained back down, eroding the crater walls.
I wouldn’t go so far to say that this indicates water on Mars, of course, since it’s indirect evidence of transient liquid water. It’s not even conclusive evidence of that. I’ve seen ditches on Earth that have eroded into terrace-like structures without rainfall; usually when the dirt has been compressed over time (like on the edge of a road) and there is some erosive force present like wind or even passing cars applying pressure and crumbling the ditch sides. There is more to this Martian story; debris on the floor of the crater looks like something was flowing, which adds to the idea of water. Maybe.
Still, it’s interesting, and worth putting into the category of "pictures motivating us to continue looking for water." Also, the full scale image shows the terrain in context, with lovely entrained sand dunes on the surface as well.
Tip o’ the Martian umbrella to Steven Charles Raine for sending me this.
April 9th, 2008 at 11:40 am
“there is some erosive force present like wind or even passing cars applying pressure and crumbling the ditch sides.”
Aha! Evidence that the Martians had cars! Proof of life on Mars.
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.
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Okay, maybe not.
April 9th, 2008 at 11:46 am
I am not a geologist (OK, aereologist)…but does that look a little like sedimentary rock in the middle there?
April 9th, 2008 at 2:27 pm
Know you’re busy Phil, but can’t believe you chose to highlight that image over the stunning HiRISE images of Phobos released today! You can see individual boulders clinging to the surface of the moon… streaks in the slopes of the famous “grooves”… bright metarial on the rim of Stickney Crater… go look!
http://hirise.lpl.arizona.edu/phobos.php
April 9th, 2008 at 3:47 pm
Why are the raw photos in black and white? Do they not have color cameras in space?
April 9th, 2008 at 3:50 pm
FWIW, I’ve seen riverine sand dunes decay in a terrace pattern from nothing more than wind and gravity. Something in the back of my mind about fine powder and static electricity from wind blowing it across dunes. Could it cause fine powder to form patterns that look like water erosion?
April 9th, 2008 at 7:34 pm
Which colors do you mean? HiRISE seems to be a CCD device, so it has several color bands including IR, not exactly corresponding to our own concepts of color.
If BAblog hasn’t a FAQ on general image processing, HiRISE has a FAQ:
April 9th, 2008 at 9:07 pm
The way Mars missions are being cut back, downsized, pushed back and flat canceled, we’ll be lucky to ever get a definitive answer.
April 10th, 2008 at 4:12 am
Frank said:
“Why are the raw photos in black and white? Do they not have color cameras in space?”
To answer this question, you have to ask a different question: What is a colour camera?
To take images in colour requires a CCD that is sensitive to colour (or, in 20th-century technology, film emulsion that is sensitive to colour). This can be achieved in two different ways.
First, you could have a CCD that contains elements that are sensitive to narrow wavebands (to obtain natural colour, this sensitivity should mimic thesensitivity of our cone cells as closely as possible). So, you might have pixels that respond to red, pixels that respond to green and pixels that respond to blue. The resulting image would then combine the three monchromatic images to form a single colour image that contains natural-looking colour. The resolution and sensitivity of such a system might be less-than-ideal, however.
So, the second option is to have a CCD that responds to a broad range of wavelengths of light, and to take images through different-coloured filters. Again, you end up with several monochrome images being re-combined to form a colour image, but you can use one CCD with many different filters to observe a very wide range of wavelengths (IIRC, the Mars rovers Spirit and Opportunity have filters to observe blue, green and infrared wavelengths. Thus, they cannot ever generate an image that appears exactly as it would to a human eye).
A raw image taken using a CCD is always monochromatic, because of the way in which a CCD works (light hitting a specific pixel generates a current that depends on the amount of light and the sensitivity of the CCD). In essence, each pixel is a light-activated transisitor (if my understanding of CCD technology is correct). Only by combining knowledge of the filter through which the image was taken and knowledge of the wavelength response of the CCD and images recorded through multiple filters can one generate a colour image.
April 10th, 2008 at 11:12 am
Since the responders seem to be in the mood to answer questions, I have a quick one. Considering that the air pressure on Mars is a fraction of what it is on Earth, how can it be sufficient to cause winds and subsequent erosion?
April 10th, 2008 at 2:13 pm
Actually it can be most anything that induces a charge, since CCD really describes the signal transfer (readout) technology - Charge Coupled Device. Essentially a CCD is an array of capacitors.
In practice you use devices that looks like MOS transistors to create the MIS capacitors (by channel capacitance), but AFAIK they don’t have source and drain areas as they don’t really need them. Charge shifting read out instead of transistor read out makes for less noise susceptibility. (Granted, you use transistors further along the signal chain. But with CCD’s you can integrate the signal first.)
And speaking of practice, it is the ubiquitous use of silicon which makes IR a natural part of a CCD photo device spectra due to its convenient bandgap.
April 10th, 2008 at 2:33 pm
I thought the impact-induced precipitation theory was a strike against liquid water on Mars (as usually understood), because it raises the possibility that all evidence of liquid water relates to impact events. The idea being that the water would last for a while (many years) because it would create a temporary greenhouse effect.
April 10th, 2008 at 10:32 pm
Wrote The BA :
“Tip o’ the Martian umbrella to Steven Charles Raine for sending me this.”
No worries! My pleasure.
It gives me a real a real buzz to be able to contribute to such a great blog - superluminous (ie,. beyond merely brilliant) write up too!
April 10th, 2008 at 10:36 pm
Asked Michael on 10 Apr 2008 at 11:12 am :
“Since the responders seem to be in the mood to answer questions, I have a quick one. Considering that the air pressure on Mars is a fraction of what it is on Earth, how can it be sufficient to cause winds and subsequent erosion?”
Well I’m not 100 % sure but my underastanding isthat it has something to do with the wind speed and possibly also the sheer fineness of the Martian dust. I think the velocity of the Martian winds make it easier to pick up the dust which is exceedingly fine grained too and this combined with the sheer length of time and absence of other erosive factors makes aeolian (wind-generated erosion) the dominant form of erosian on Mars.
April 11th, 2008 at 12:21 am
The location incidentally is near Mojave crater.
April 11th, 2008 at 10:52 am
Michael writes:
Considering that the air pressure on Mars is a fraction of what it is on Earth, how can it be sufficient to cause winds and subsequent erosion?
Steven Charles Raine is right. The surface dust is fine and the thinness of the air means less air resistance, so dust storms can hit surface features at hundreds of kph. And with little water erosion, and next to zero oxidation, there’s plenty of time for wind erosion to work.
April 15th, 2008 at 8:14 am
All stars in space have 21 crystals in their center.