JPL Scientist's Explanation
Of The 'Tubes' On Mars
From Robert Collins

Subject: More handwaving?
Date: 3-9-01
From: Dave Pieri
To: rcollins
Dear Robert
This is a professional interpretation based on having labored over literally thousands of Viking Mars Orbiter Images, hundreds of Mars Observer images, many, many, many Landsat, ASTER, and airphotos of the earth, having studied aeolian and fluvial geomorphology at the graduate level at two universities, and well over 20 years of aerial and orbital photointerpretation and optical and radar remote sensing here at JPL/Caltech--and years of field experience in a range of climatic zones from desert to arctic. Also, the subject of my Ph.D. thesis was (the first) systematic global study of martian valley networks, in which I looked at thousands of features, such as the one in the MGS image, over a period of years.
Realize one critical fact--these are not "tubes"...the positive relief is an ILLUSION--the area is crossed by concave valleys. The transverse dune trains are emplaced on the valley floors--this is not new, either or Mars or the Earth. It even occurred at very small scale in the Viking Lander 1 site in Chryse Planitia...not all that far away from where this MGS picture was taken.
Look carefully at how the craters in the larger reference image are lit. Then look at the valley wall shadows. Seeing inverted relief is an easy mistake to make, even by an experienced photointerpreter--at first glance. That's why it's always important to check one's first impression against obvious features in the landscape to get oriented properly.
Also, the picture on the "Enterprise" web site is hopeless.
Way overstretched, saturated, and doesn't show other relevant parts of the scene. I downloaded the original data at full resolution from Mike Malin's web site in La Jolla, then used a square-root stretch to even out the contrast. It's clear that these crescentic dune-lets populate the landscape--and occur in all the low troughs or valleys throughout the image (take a look at the subscene attachment). They are a variety of sief and nearly barchan dunes--dead ringer analogs to those in terrestrial deserts. Turn the image 180 degrees (vs. the "Enterprise" picture) so that valleys look like valleys and craters look like craters, not bumps. The 3D striated "glass worm" illusion vanishes, and we're left with a fairly mundane image, exciting only to those of us who have studied the morphology of the valley networks on Mars.
Dunes follow aerodynamic principles--therefore they DO often line up in really precise, repetitive ways related to aero/hydrodynamic streamlines and standing wave resonances.
****** David C. Pieri, Ph.D. Earth and Space Sciences Division Mail Stop 183-501 Jet Propulsion Laboratory 4800 Oak Grove Drive Pasadena, CA 91109 USA FAX: 818-354-0966 VOICE: 818-354-6299


This Site Served by TheHostPros