SPSR paper abstracts

Fri, 23 Jul 1999 20:27:20 EDT

Analysis of Landforms in Cydonia Mensa
Crater, H W, McDaniel, S V, Carlotto, M J (P42A-09) :

Abstract: Analysis of landforms in Cydonia mensa reveals a variety of features whose probable means of formation is ground-ice and perhaps liquid water erosion. Some evidence of faulting exists. We examine and compare some of these landforms. We show that a group of mound-like formations in the Cydonia area of Mars, of relatively small and nearly uniform size, have relative positions that repeatedly display symmetries in the apparent form of related right and isosceles triangles. We also show that these pairs cluster sharply in density about a certain value of the defining angle of those related triangles and that on average the vertices of the triangles lie significantly closer to the measured centers of the mounds than those for fictitious mounds from a computer simulation. Our computer simulation of the surrounding features and the mound formations themselves demonstrates that the numerous examples of these symmetries, the resultant clustering about certain proportions, and the relative precision of the vertices to the mound centers are not compatible with random geological forces. We have thus uncovered an anomaly of number, geometry and precision. The level of significance we find for our test is p~15.5/1,000,000 .

Evidence for a Paleo-Ocean Shoreline, Sedimentary Features and Water Erosion in Cydonia
Erjavec, J and Brandenburg, J E (P42A-10)

Abstract: Mars Global Surveyor (MGS) images of the Cydonia Mensae region of Mars have provided evidence that suggests surface water activity of a long duration. Scarp lines identified by Viking, considered as possible shoreline features (1), have been reanalyzed using the higher resolution MGS images. The scarps define a boundary between two different terrain types, one representing a knobby terrain (highland) and the other a possible paleo-ocean(2) (lowland). Because of the persistence of the curvilinear scarps and their offset from the knobby terrain which they circumvent, they cannot easily be regarded as simple remnants of eroded knobby terrain. The scarps appear similar to strandline or shoreline features which occur on earth. That interpretation is supported by the morphological characteristics of the two terrain types they dissect.

Volcanic flows have been suggested as explanations for many of the varied terrain types on mars, including kilometers of layered rocks in the Valles Marineris. In the Cydonia region, volcanic flows are not likely as land- forming mechanisms. There appear to be no significant volcanic sources in this region nor can the distinctive erosion morphologies of many of the landforms in Cydonia be easily attributed to volcanism. To the contrary, some of the erosion appears to be structurally controlled, perhaps by faults, layered rocks or even folded sediments. Furthermore, evidence for both erosion and deposition by water is strong in Cydonia. Terraces (wave-cut?), benches, probable sedimentary layering, stream channels and other water erosion features have been found in the MGS images.

Evidence also exists for both precipitation and surface runoff. Apparent rills are found on some of the landforms and they appear markedly similar to rill types found in sedimentary terrains in the western United States. Still, caution must be taken when using strict earth-based analogies for martian terrains. If martian terrains developed under a gravitational field that was only 1/3rd that of the earth, can we be certain that depositional and erosional environments on the earth directly correlate to similar environments on mars? Taking that into consideration and despite strong evidence for water in Cydonia, we propose that the typical tributary stream networks common on earth may not be as common on mars on the basis of the different gravitational field strength.

Ice Found in Crater in Cydonia
Moore, H L, Brandenburg, J E, Corrick, S, Sirisena, A (P42A-15 )

Abstract: Review of recent Mars Global Surveyor images taken on April 23, 1998 has revealed unusual surface craters located at 40.9 degrees north latitude and 9.9 degrees west longitude. Unusual crater features disclosed in the recent MGS Image (strip No.3, Cydonia) indicates that water ice features may exist in the Cydonia area and appear to correlate to similar features in Iceland. Specific crater features found include, a smooth, flat floor surface, high albedo floor surface, a reflection of the floor surface on the crater wall, no apparent ejecta apron, and steep crater walls. Several studies have identified and compared surface features on Mars to like features on Earth, which contain water ice, including features on the landmass of Iceland (Frey Et Al, 1979; Hodges and Moore, 1978). Other studies indicate that there is a high probability of water ice at latitudes greater than 40 degrees north on Mars (Carr, 1981; Allen, 1979; Soderblom and Wenner, 1978).

Several possible explanations for the presence of water ice in the floor of the subject crater are presented. Two scenarios presented involve a meteor or comet hitting the surface and excavating the crater. The meteor/comet impact is suggested to be significant enough to generate heat to either: (a) melt water ice in the regolith and bedrock or (b) crack the crust to permit molten rock to reach close enough to the surface materials to melt frozen water in the bedrock and soil which then flowed into the crater and re-froze. This new frozen surface forms the current flat crater floor.

Another idea presented is the possible daily melting of near surface ice in the soil and rock. This is supported by recent new evidence from the NASA Pathfinder project that shows that temperatures on the surface of Mars reach 20 degrees C. in places, making melting of surface water ice possible. Also discussed is the possible establishment of a water table frozen in place at some point in the geologic history of Mars.

(Mac Tonnies)