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Date Entered: July, 1989
Date Last Revised: March 25, 1991
This site is dominated by Hesperian ridged plains material, which contain numerous north-south trending wrinkle ridges of the Xanthe Dorsa system. These materials have been suggested by numerous authors as being volcanic (basaltic) in origin. Highland materials and other sediments washed down by the formation of surrounding outflow channels may also be present in the vicinity of the proposed landing site. The lithology of the source rock is presently unknown, but possibilities range from komatiites to anorthosite.
Scientific Rationale
Hesperian ridged plains are an extensive geologic unit on Mars and are used as the referent for the Hesperian period. An absolute age date of these materials would act as a "guide fossil" and would be useful in correlating the absolute ages of other martian periods. Because a large number of outflow channels have debouched into Chryse Planitia and because Chryse Planitia is one of the lowest areas on the surface of Mars, standing water may have been present in the vicinty of the proposed landing site long after other areas on Mars became dessicated. As a result, Chryse Planitia may be an excellent location for finding ancient fossil organisms. Design of future spacecraft is aided by the "ground truth" observations made by the Viking landers. Besides being an ideal location for conducting experiments and obtaining samples complementary to the Viking lander results, the low elevation of the landing site and low northerly latitude (i.e., direct line-of-site communication) make the proposed landing site engineeringly simpler than other areas on Mars. (See R.A. Craddock, Rationale for a Mars Rover/Sample Return Mission to Chryse Planitia and the Viking 1 Lander, Lunar and Planetary Science, XXI, 234-235, 1990.)
Objectives
Target A. Objective: Land 2 km north of the Viking 1 landing site at 22.52 deg. , 47.97 deg. . Obtain contingency sample of Hesperian-age ridged plains to depth (~1 m). Probability of Success: Very High. Depends on successful landing of rover and return vehicle, which is aided by surface photographs obtained by Viking 1.
Target B. Objective: Obtain ejecta sample from crater formed by jettisoned Viking aeroshell located approximately 1 km south of the proposed landing site (or approximately 1 km north of the Viking 1 landing site). Collected samples would represent material to a depth of approximately 2 m. Probability of Success: High. Depends on targeting ability before and after landing.
Target C. Objective: Obtain sample of the Viking 1 lander (e.g., latch pin which held sampler shroud to lander) to determine weathering rates on Mars, obtain soil/rock samples from Viking landing site, conduct range of complementary science experiments in the vicinity of the lander (e.g., weather), photograph the lander, and send radio commands to turn lander antennae back towards Earth. Probability of Success: High. Depends on ability to direct rover to Viking 1 position. Trafficability will be poor based on Viking photographs, but unless new surface photographs are obtained, rovers will probably be built to negotiate these types of terrains due to the similarity of the Viking 1 and 2 landing sites. Return to MRSR landing site (Target A) before beginning the second phase of the mission.
Target D. Objective: Obtain samples of Xanthe Dorsa ridge from proposed landing site to San Juan crater. Photographs of the ridge in various places may aid in the understanding of ridge formation. Ejecta material from San Juan would represent material to a depth of approximately 50 m. Probability of Success: High. Depends on the performance of the roving vehicle in rocky terrain. Navigation could be aided by using the "dead reckoning" potential of the wrinkle ridge.
Target E. Objective: Obtain ejecta samples from the rampart crater Yorktown to determine possible ejecta flow mechanism (e.g., volatiles in target material). Observe distribution of coarse/fine material during traverse to determine possible Chryse channel-forming mechanism(s). Probability of Success: High to Moderate. Depends on durability of rover. Return to landing site (Target A) to complete second phase of the mission.
Potential Problems
Engineeringly, the proposed mission is limited mainly by the rugged terrain in Chryse Planitia. Rovers will have to be very durable and capable of navigating around large obstacles. However, because Viking 1 (Chryse Planitia) and Viking 2 (Utopia Planitia) represent the only information that is currently available about the true nature of the martian surface, it seems logical to assume that--at least initially--soft landers will be designed to operate in such environments. Scientifically, many interesting experiments could still be performed in the vicinity of the Viking 1 lander. Ultimately, however, opposition against returning to a site previously visited by spacecraft because we have seen it, and to Chryse Planitia in particular because it is "dull" (i.e., there are no volcanoes, terraced deposits, etc. on the horizon), may prevent such a mission from occurring.
Trafficability
3.
Estimated Traverse Distance
100 km.
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