Interest in the history of water activity on Mars is driven by the question of whether evidence of life, past or current, can be found on another planet. Mapping of drainage patterns and associated deposits in Margaritifer Terra provides evidence of ancient aqueous activity that may be analogous to processes occurring on the Earth. Margaritifer Terra is located at the eastern end of Valles Marineris1 and is characterized by well-preserved valleys, channels, as well as geological features like impact craters that appear to have been erosionally modified by water.
Figure 1. Timeline indicating the relative age of events shaping the surface in the Margaritifer Terra region2
To place the assessment of the Margaritifer Terra drainage systems in proper context, the geological history of the region is evaluated via careful mapping. Relative ages of various surfaces and features are determined through cross-cutting relationships and crater statistics. In summary, ancient multi-ringed impact basins represent the oldest features and were followed by four resurfacing events. The third and fourth of these resurfacing events help constrain the age of channel and valley formation, including the largest channel, Uzboi Ladon Morava (ULM), and valley system, Parana-Loire Valles. Because the ULM system was already active at the time of the Holden crater formation it contributed to formation of at least one lake within the crater2.
Using data from the Mars Global Surveyor (MGS) and Mars Reconnaissance Orbiter, channel gradients and cross-sections can be measured1-3. Researchers employ these measurements to determine estimates of the ancient water system's various mean velocities and ultimately, the amounts of water released. For two of the larger channels in Margaritifer Terra, Ladon and Morava Valles, velocities of 3.2-6.7 m/sec and 2.5-5.3 m/sec were calculated, respectively1-3. These velocities are equivalent to or above velocities measured in the Mississippi1-3, but below those derived for larger Martian outflow channels being studied elsewhere. Meanwhile, the calculated discharge rates for these large channels in Margaritifer Terra exceed that of the Mississippi River on Earth by a factor of five2.
Figure 2. (a) Layering in ancient lake sediments on the floor of Holden Crater2. The layers are thin and continuous over distances of up to kilometers, consistent with emplacement in standing water. (b) Large bed forms were deposited where alluvium was washed into the crater as water impounded in Uzboi Vallis breached Holden's rim. Both images are subsets of MOC image M0302733, centered at 27.1° S, 34.9°W and 2.8 m/pixel resolution.
One area of special interest in Margaritifer Terra is Holden crater and the region to the south along Uzboi Vallis, where there appears to have been multiple, ancient lakes3-4. Holden's formation initially disrupted the ULM system3, however the crater appears to have partially filled with water and sediment both before and after a breach was formed in the rim and water stored in Uzboi Vallis to the south drained onto the crater floor4. Whether the finely layered deposits within the crater walls are evidence of standing water, such as in a lake environment, or a result of deposits due to slowly flowing water remains under discussion, but either possibility reflects deposition in a fairly quiet water setting.
Figure 3. Fine scale beds exposed on the floor of Holden crater were likely deposited in an ancient lake. Persistence of such a lake points to conditions that would have been much more clement that currently are found on Mars and may point to habitable conditions early on in the planet's history. Portion of HiRISE image PSP_003077_1530_IRB showing eroded alluvial fan materials overlying phyllosilicate bearing, probable lacustrine deposits in Holden crater, Mars. False color created using data from the RED (image scale of 26 cm/pixel), IR, and BG CCDs (image scale 52 cm/pixel) on the HiRISE camera. Scene is approximately 750 m across and north is up.
The well-preserved ancient valleys and channels in Margaritifer Terra, especially Holden Crater which was one of the final candidate landing sites for NASA's Mars Science Laboratory mission, presents a location with potential evidence of habitability and remains an area of continual investigation and study.
Water activity in the Margaritifer Terra region continued into the relatively more recent late Hesperian-to-early-Amazonian. Unlike prior activity, however, which saw the formation of the ULM and other valleys, this late activity was largely confined within craters and resulted in the formation of alluvial fans5-6. These fans of sediment flank portions of crater walls and appear similar in form to fans of debris washed out of mountains in Death Valley on the Earth.
Citations1. Grant, J.A., and Parker, T.J., 2002, Drainage Evolution of the Margaritifer Sinus Region, Mars, J. Geophys. Res., 107, 10.1029/2001JE001678.
2.Irwin, R. P., III, and J. A. Grant (2013), Geologic Map of MTM –15027, –20027, –25027, and –25032 Quadrangles, Margaritifer Terra Region of Mars, U.S. Geol. Surv., Scientific Investigations Map 3209 (in press).
3. Grant, J. A., R. P. Irwin, III, J. P. Grotzinger, R. E. Milliken, L. L. Tornabene, A. S. McEwen, C. M. Weitz, S.W., Squyres, T. D. Glotch, and B.J. Thomson, 2008, HiRISE imaging of impact megabreccia and sub-meter aqueous strata in Holden Crater, Mars, Geology, 36, 195-198, doi: 10.1130/G24340A.
4. Grant, J. A., R. P. Irwin, III, S. A. Wilson, D. Buczkowski, and K. Siebach (2010), A lake in Uzboi Vallis and implications for late Noachian-Early Hesperian climate on Mars, Icarus, 212, 110-122, doi:10.1016/j.icarus.2010.11.024. 5. Grant, J. A., and S. A., Wilson, S. A. (2011), Late alluvial fan formation in southern Margaritifer Terra, Mars, Geophys. Res. Letts., 38, L08201, doi:10.1029/2011GL046844. 6. Grant, J. A., and S. A., Wilson, S. A. (2012), A possible synoptic source of water for alluvial fan formation in southern Margaritifer Terra, Mars, Planet. Space Sci., 10.1016/j.pss.2012.05.020.