Mars Global Surveyor
Once again Martian gullies are in the news. A NASA press release issued August 24, 2005 announces that a NASA Study Shows Water Could Create Gullies on Mars. This latest news centers on a presentation to be delivered at the upcoming American Astronomical Society's Division for Planetary Sciences meeting.
The principal author of the study "Formation of Martian Gullies by the Action of Liquid Water Flowing under Current Martian Conditions" is Jennifer Heldmann of the NASA Ames Research Center. Using numerical models, they have come to the conclusion that the gullies in question could have been formed by the action of liquid water. This issue first came to the forefront in June 2000 when Science magazine featured the article "Evidence for Recent Groundwater Seepage and Surface Runoff on Mars" written by Michael Malin and Kenneth Edgett. The cover image used for that issue of Science is recreated in the Orbital Gallery entry Martian Gully Surprise.
There were three Mars Global Surveyor (MGS) images that accompanied the NASA press release. The image that caught my attention was the MGS Narrow Angle camera close-up that shows the alcove, channel, and debris apron structure in a crater wall. The two things that struck me were first that the image was in black and white, as are all Narrow Angle Camera images because that camera has no color capability, and second that the image was very closely cropped to the gullies.
I therefore resolved to create a version of that image that would be both in color and show the crater in which the gullies are located in its entirety.
Source Image Background
The image shown at the left is my rendition of the original source image that was taken by the Mars Global Surveyor Narrow Angle camera in July 2000. The width of the terrain seen in the image is almost 3 kilometers. Note that I have cropped the image top and bottom to the margins of the crater rim. The MGS Image ID for this picture is M17-00423. The raw version of this image had a pixel aspect ratio of 1.6 which has been corrected for in the images shown here.
The main feature seen in this image is a crater that is located at 39.2° south latitude and 200.9° west longitude. The gullies shown in the NASA press release are on the northern wall of the crater. In the image shown here, north is towards the top and the crater wall with the gullies appears near the top edge of the image.
All work on this image was performed in Adobe Photoshop. Please note that this is a false color rendition of the MGS NA image. This is necessary because the MGS NA camera provides no color information in the pictures that it takes. The colors that I used to create my version of the image were selected based on colorized versions of other Mars Global Surveyor Narrow Angle Camera images. The non-cropped, full size print version of this picture is 4.6 inches wide by 30.2 inches tall at 360 ppi as compared to the original source MGS image which has a print size of approximately 2.8 inches by 11.7 inches.
Because I had to crop, reduce and compress the full frame image so much in order to have it fit on this page, I decided to make available a highly-compressed, but full size wallpaper version of just that portion of the crater wall that contains the gullies described in the paper. This wallpaper image is made available for your personal use only. It is not to be modified or redistributed in any form by any means. All rights are retained by the artist.