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- to 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.
Introduction
Beginning in April 1998 NASA initiated an imaging project to re-photograph the Cydonia region on planet Mars. Results of the imaging process produced three high- resolution strip images of the Cydonia area. This discussion centers on crater features in the bottom half of the 3rd MGS image taken on April 23,1998 (Figure 1)(http://www.sun.com/mars/mgs/target/CYD3/index.html).
Previous work has established martian analogs of terrestrial pseudocraters produced by the interaction of lava flows with water or ice (Frey, Lowry and Chase, 1979; Allen, 1979). Several studies have identified and compared surface features on Mars to like features on Earth, specifically on the landmass of Iceland (Allen, 1979; Hodges, 1977; Hodges and Moore, 1978; Williams, 1978).
Unusual crater features disclosed in the recent (April 1998) MGS Image strip No. 3 indicate that water ice features may exist in the Cydonia area and appear to correlate to similar features in Iceland.
Discussion
The Cydonia region of Mars has been one of the areas of Mars that has been scientifically studied in great detail (Frey, Lowery, and Chase, 1979). The general interest in this area of Mars centers on anomalous surface features that include unusually shaped mesas, geometrically positioned mound structures, pseudocraters, lineaments, and pyramidal shaped structures.
While viewing (on close inspection) the 3rd MGS image, the author noticed several unusual craters clustered just north of the large ridge in the upper portion of the bottom image (Figure 1). The approximate geographic location is 40.9 degrees north latitude, 9.9 degrees west longitude.
A total of three craters were found in this cluster that exhibit an unusual floor surface. The craters are somewhat circular in shape and very steep walled. No splash or ejecta apron was observed. There appears to be a very slight up turned “lip” around the crater with only minimal difference in elevation with the surrounding plain.
In Carr, 1981, a discussion of impact crater types and volcanic craters does not include the types recently found and included in this discussion. These new crater types are perhaps a hybrid of previously identified types.
A specific crater identified in this study (Figure 2) contains a floor which appears to be composed of different material than the crater walls. Upon closer inspection it was disclosed that the crater floor had a different and higher albedo than the walls of the crater and the surface of the surrounding plain. It was also noted that there was a patch of high albedo material on one portion of the crater wall. This high albedo “patch” was determined to be a possible reflection of ambient light reflected from the crater floor.
Crater Floor
The floor of the crater was determined to be a different material, based on the albedo and the surface texture. The albedo of the floor material is quite high as compared to the crater walls and surface materials. The crater floor also was found to have a very smooth surface and formed a distinct boundary where the floor met the crater wall.
As viewed from the spacecraft, the craters (in the crater cluster discussed above) appeared to have either fluid or some smooth solid on their floors. Being that the surface temperature on Mars is usually below the freezing boundary for water, frozen water would be the likely solid if water were present. Molten rock material would also be a source of fluid material (lava).
Another crater with similar morphology was located to the east of the above discussed crater cluster, near 40.95 degrees N. latitude, 9.5 degrees longitude (Figure 3). This crater has a much wider diameter and shows signs of some high albedo ejecta material. It does, however, have a high albedo crater floor, which is very smooth. The crater floor is slightly domed and appears to also reflect light onto the crater wall. The significance of this second site is to show that the possible presence of water ice in the craters may not be isolated but more wide spread that previously thought.
The Presence Of Water Or Water-Ice
It is postulated by several workers that evidence exists for large amounts of water, water-ice, and carbon dioxide which may be stored in the near-surface rocks and regolith on Mars (Allen, 1979; Carr, 1981; Carr and Schaber,1977; Frey,1979; Levin and Levin, 1998; Hodges and Moore,1979; Masursky et al., 1977; and Soderblom and Wenner,1978).
It was disclosed by Carr (1981) that water ice could exist at relatively shallow depths (a few tens of centimeters) at latitudes greater than 40 degrees. Frey (1979) suggests that in the Cydonia region interaction of thin lava flows with near surface permafrost or ice may have produced explosions, which resulted in low mound features that correlate to similar features in Iceland.
In addition, Hodges and Moore (1979) suggest in their study of the area around Olympus Mons that the interaction of magma with ice could have created vast meltwater lakes with frozen surfaces. Further, they suggest a former existence of more extensive glacial ice than has been measured or inferred.
More recently, Gilbert Levin and Ron Levin (1998) have formulated a model that predicts the dinurnal presence of several tenths of a percent to several percent water moisture in the thin, topmost layer of the surface material over large regions of Mars. They also postulate that if liquid water does form that it would pool in low areas.
William Hartman and Gilbert Esquerdo (1999) identified surface craters on Mars, which may suggest processes of deformation involving ice on Mars. Their scenario suggests that early Mars had a very ice-rich permafrost layer and suggest a model for the formation of ice in surface craters (Figure 4 and Figure 5). These craters, they point out, develop a pool of water, which then freezes and forms a flat floor in the crater. Wind blown dust then forms a thin cover over the ice layer.
The 1997 NASA Pathfinder’s meteorological station on Mars revealed data that supports the concept of environmental conditions favorable for liquid water at or near the surface. Their data revealed air temperatures ranging up to 21 degrees C at the surface (Mars Pathfinder Mission Status, 1997).
It was also reported (Malin Space Science Systems, 1998) that a crater in the Southern Hemisphere of Mars (located and photographed by the Mars Global Surveyor) probably once held water. It was suggested by Malin and his research team that the Southern Hemisphere crater, which has channels in the walls and dark sediments on the floor, was probably carved by torrents of water that seeped into the crater forming a pool that evaporated eons ago.
The point of these references is that the probability of water ice near the surface of Mars, and especially at latitudes greater than 40 degrees, is quite high.
TERRISTRIAL COMPARISONS
Comparisons of planetary landscape features with terrestrial features provide researchers with possible insight into the origins of these extraterrestrial geomorphic surfaces. Previous works on similar geomorphic landscapes found on Mars and Earth have been made (Carr, 1981; Frey, Lowry, and Chase, 1970).
These researchers often use the landscape of Iceland to make comparisons between these two planets. A search of the literature for published work on Mars resulted in locating an image, taken over Iceland, that has very similar features when compared to the ice craters discussed in this paper. The image selected for this comparison is found in the paper Pseudocraters on Mars by H. Frey, B. Lowry, and S. Chase in 1979 (see the List of References this paper).
The comparison image (Figure 6; Frey, Lowry, and Chase,1979 credit the image to C.C. Allen, Volcano-ice interactions on the Earth and Mars, PH.D. thesis, Univ. of Ariz., Tuscon,1979) shows an area of Iceland near Lake Myvatn where there are several craters in the landscape, which appear to be of volcanic origin. The craters, however, have frozen water in their floors (Figure 7)), which show up in morphology like the subject craters in Cydonia. It is not suggested that the origin of the craters is the same, but that the craters have been subjected to an inflow of water (groundwater and/or snow and rain) which has subsequently frozen to form the floor surface.
CONCLUSIONS
As a result of the above discussion several possible scenarios for forming the crater floor feature are proposed.
First, an impact of a meteor or comet hit the surface excavating a crater into the surface material. The heat of the impact either melted frozen water in the crust (permafrost) which filled the crater to the current “water table”, or opened the crust sufficiently to permit liquid water in the crust to flow into the crater. Within a short time the water froze and remains as a solid today – with a high albedo. It is acknowledged that the thin atmosphere makes water ice at the surface tenable except at the poles (north).
Secondly, an impact of a meteor or comet hit the surface, excavating a crater into the surface material. The force of the impact penetrated sufficiently into the crust to crack the crust and disrupt molten material, which flowed into the subsurface vicinity of the crater. Consequently, the molten material solidified and now forms the smooth floor of the crater or melted near surface water ice, which flowed into the crater forming the crater floor. In opposition to the theory that basalt forms the crater floor is the fact that the molten rock material is very likely to be dark (basalt) in contrast to the crater floor observed in the image which is light colored. Ice or frost would normally have the high albedo as recorded on the image.
A third possible explanation is that the water ice gradually seeped into the crater over many thousands of years as near surface temperatures daily warmed the frozen water trapped in the soil. Each warm day the water migrated to the lowest position available in the surface – craters. Each night the water would refreeze then be subject to melting the next day and continue this cycle as seasonal cycles availed.
Another scenario is that the flat floor of the crater represents a possible water table, frozen in place. This is thought to have taken place at some point in the geologic history of Mars. However, this scenario will need much more data and evidence, obtained from surface and subsurface exploration, to be corroborated and stand as fact.
Finally, it is suggested that this new found crater cluster in the Cydonia area may represent the location of near surface water-ice that is much closer to the surface and in greater quantities than previously thought. The implications for this very near-surface water ice would be a tremendous encouragement for the future exploration of Mars. This subject area might make an ideal location for the first human colonization, given optimal Mars temperature in this latitude, and now possible available water.
The strong possibilities of water ice exhibited by these craters suggest that further examination of this feature by spectrographic analysis, additional imaging and possible surface exploration is warranted and encouraged.
Acknowledgements
The author gratefully acknowledges the contributions and support of several persons in making this paper possible. Dr. Horace Crater, University of Tennessee Space Institute, Dr. Stanley McDaniel, Sonoma State University, California, Dr. John Brandenburg, plasma physicist, and Mr. Jim Erjavic, geologist and GIS analyst, are greatly appreciated for their review and discussion of the paper. Ananda Sirisena, independent image processing engineer, England, reviewed the original MGS crater image and provided expert evaluations on the reflection feature and albedo of the crater floor. Mr. Steve Corrick, Mind Into Matter, Inc. is acknowledged for his discovery of the reflection feature on the crater wall. Finally, the author wishes to thank NASA for their willingness to not only reimage the Cydonia region on Mars but to also make the image information available to the public.
References
Allen, Carlton C. Volcano-ice interactions on Mars. J. Geophys. Res., Vol.84,No. B14,pp.8048-8059, 1979.
Carr,Michael H., The Surface of Mars. Yale University Press, New Haven, CN, 1981.
Carr,M.H., and G.G. Schaber. Martian permafrost features. J. Geophys. Res.,Vol.82,No.28,pp 3985-4015,1977.
Frey, Herbert, Barbra Lowry, and Scott Chase. Pseudocraters on Mars. J. Geophys. Res., Vol 84, No. B14, pp. 8075-8086, 1979.
Hartman, W.K., and G. Esquerdo. “Pathological” Martian Craters: Evidence for a Transient Obliteration Event?. Meteoritics and Planetary Science, Vol. 34, No. 2, pp.159-165, March, 1999.
Hodges, C.A. Basaltic ring structures of the Columbia Plateau and possible extraterrestial analogs. In Lunar Science VIII,pp.449-451, Lunar science Institute, Huston,Tex., 1977.
Hodges, C.A., and H.J. Moore. Tablemountains of Mars (abstract), in Lunar and Planetary ScienceIX, pp. 523-525, Lunar and Planetary Institute, Houston, Tex.,1978.
Hodges, Carroll A., and Henry J. Moore. The subglacial birth of Olympus Mons and its aureoles. J. Geophys. Res. Vol. 84, No. B14, pp.8061-8074, 1979
Levin, Gilbert V., and Ron L. Levin. Liquid water and Life on Mars, presented at the Annual Meeting of the Society of Photo-optical Instrumentation Engineers (SPIE), San Diego, Calif., July, 1998.
Malin Spce Science
Systems (MSSS), NASA, website reportsApril1-Dec. 31,1998 (web site: http://mpfwww.jpl.nasa.gov/mgs/msss/camera/images/5_27_98_agu_release/index.html).
Mars Pathfinder Mission Status, Jet Propulsion Laboratory, NASA, daily website reports, July 9-Aug.1, 1997.
Masursky, H., J.M. Boyce, A.L. Dial, G.G. Schaber, and M.E. Strobell. Classification and time of formation of martian channels based on Viking data. J. Geophys. Res., Vol. 82, pp. 4016-4038,1977.
Soderblom, L.A., and D.B. Wenner. Possible fossil water liquid-ice interfaces in the martian crust. Icarus, 34,pp.622-637, 1978.
Williams, R.S. Geomorphic processes in Iceland and on Mars: A comparative appraisal from orbital images. Geol. Soc. Amer. Abstr. Programs, 10(7), pp.517, 1978.
Figures
Figure
1. This image shows the subject crater cluster with several flat bottomed
craters (lower center, upper left, lower right) suggesting that the floor
material was possibly fluid in the past. It is postulated that the material
in the floor of the craters is water ice.( Image courtesy of Malin Space
Science Systems/NASA)
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Figure
2. This April 1998 MGS photo shows a possible location of water-ice
in a crater in the Cydonia area of Mars. Note the high albedo of the floor
surface and the apparent reflection of the floor surface on the crater wall.(Image
courtesy of Malin Space Science Systems/NASA)
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Figure
3. This image shows a possible second area where water ice may
compose the floor of a crater. This crater is located near 40.95 north latitude
and 9.5 degrees longitude.( Image courtesy of Malin Space Science Systems/NASA)
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Figure
4. This cluster of craters located in northern Iceland near Lake Myvatn
shows very similar morphology to the subject craters in Cydonia. Of particular
interest is the lower most crater in the upper right hand of the image.(Image
from Frey, Lowry, and Chase, 1979)
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