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Mars Polar Science 2000 4113.pdf

AFTER THE POLAR : WHERE TO NEXT? D. A. Paige, Dept. of Earth and Space Sciences, UCLA, Los angeles, CA 90095. [email protected].

Introduction: The recent loss of the Mars Polar lished to date have been particularly exciting. MOLA Lander (MPL) mission represents a serious setback to topographic maps show that both polar caps have ap- Mars science and exploration. Targeted to land on the proximately 3 km of total relief; and have shapes that south polar layered deposits at 76° S latitude are consistent with those expected for large ice sheets. and 195° W , it would have been the first The MOLA data also suggest that both caps may have mission to study the geology, atmospheric environ- been significantly larger at some point in their past ment and volatiles at a high-latitude landing site. history [1]. The north polar cap lies in a regional Since the conception of the MPL mission, a Mars ex- topographic depression which may have once held an ploration strategy has emerged which focuses on Cli- ancient ocean. The south polar deposits lie on a re- mate, Resources and Life, with the behavior and his- gional topographic high[ 2] , and show distinct evi- tory of water as the unifying theme. A successful MPL dence for glacial flow [1]. Both polar regions show mission would have made significant contributions evidence for the outflow of liquid water into sur- towards these goals, particularly in understanding the rounding depressions [2]. In the south, the flow of distribution and behavior of near-surface water, and water can be traced into the Argyre basin, and then the nature and climate history of the south polar lay- across the equator into the northern lowlands [3]. The ered deposits. Unfortunately, due to concerns re- high-resolution MOC images of the north and south garding the design of the MPL spacecraft, the rarity of polar caps show a diverse array of fresh surface tex- direct trajectories that enable high-latitude landings, tures on the residual caps and associated layered de- and funding, an exact reflight of MPL is not feasible posits which suggest that the polar regions are not within the present planning horizon. However, there presently being “mantled” by dust and ice as thought remains significant interest in recapturing the scien- previously, but instead are being actively modified by tific goals of the MPL mission. The following is a processes that have as yet, been not defined [4,5]. In discussion of scientific and strategic issues relevant to total, the MGS data suggest that the Martian polar planning the next polar lander mission, and beyond. regions we see today are the product of a complex Volatiles and Atmospheric Measurements: MPL climatological and hydrological history which may be included the most sophisticated package of meteorol- intimately connected to the climatological and hydro- ogy and volatile-sensing instruments ever flown. Its logical history of the planet as a whole. deployment at a high-latitude landing site during the Polar Landing Sites: MPL was the first Mars late spring season would have provided the first op- mission whose scientific strategy was driven by the portunity to characterize global-scale weather patterns desire to obtain detailed measurements at a pre-chosen in the southern hemisphere, as well as measurements landing site. Because of their extensive geographic of the abundance of water ice and adsorbed water and extent, and the expected uniformity in their morpho- carbon-dioxide in the soil, and water vapor in the logical characteristics, the south polar layered deposits overlying atmosphere. These would have been com- represented an excellent target for the first polar bined with orbital atmospheric sounding and general lander mission. The north residual cap is another circulation models to provide a much better picture of good example of a large, relatively homogeneous tar- the behavior and distribution of . In- get. However, as we study the Martian polar regions in situ measurements like those intended by MPL are the greater detail, it is becoming clear that to sample the only means of obtaining this type of information, and true diversity of polar terrains, and to reconstruct the should definitely be repeated in future polar lander geologic and climatologic history they may contain, missions. many more landings will eventually be required. In MGS Results: In 1995, when the concept for the many cases, a precision landing with an error ellipse MPL mission was originated, our understanding of of less than 5 km would be required to enable detailed Mars was based almost exclusively on then Viking examination of specific features of great scientific and datasets. Since that time, the Mars interest, i.e. an exposure of layers or a suspected an- Global Surveyor (MGS) orbiter has provided signifi- cient outflow channel or esker deposit. cant new datasets which are revolutionizing our un- The Desirability of Landing Robustness and derstanding of the planet. The MGS results in the Mobility: One of the key new pieces of information north and south polar regions that have been pub- that the MGS MOC images have provided, is that Mars Polar Science 2000 4113.pdf

AFTER THE : D. A. Paige

polar terrains that appear to be smooth and homoge- erful technique that can be extended to true micro- neous at 1000m scales, are definitely not smooth and scopic resolution on future payloads. homogeneous on 10 m scales. Figure 1 shows exam- Future polar lander payloads should also include ples of high-resolution textures in the north and south newly-developed instruments which could take ad- polar regions revealed by MOC. vantage of the sample acquisition and analysis capa- bilities of the MVACS payload in a complimentary manner. For example, the addition of an organics detection experiment could significantly extend the search for near-surface organics begun by the Viking landers during the 1970’s to environments that could have a greater potential for the preservation of organ- ics. Conclusions: While the near-term prospects for recovering the scientific objectives of the MPL mis- sion are uncertain, it is clear that an integrated scien- tific strategy to study Mars’ climate, resources and life must include detailed study of the polar regions at multiple landing sites. The MGS results indicate that both the north and south polar regions contain a num- ber of sites of high-scientific interest, and that with foreseeable improvements in our capabilities for ro- bust, precisely-targeted landers, these sites should be accessible to the next generation of Mars landers. The scientific strategy advocated here is basically an ex- tension of that originally employed for MPL. It starts Figure 1. MGS MOC images of surface textures at with the selection of a specific landing site of high- the Martian north residual water ice cap (top), and scientific interest, followed by the design of a flexible south polar layered deposits (bottom). [6] integrated payload package that is capable of charac- The implications of this new information are two- terizing its environmental conditions, the abundance fold. First, a robust landing system will be required to and behavior of its volatiles, and the fine-scale com- ensure safe landings on most polar terrains. Second, a position and geology of its deposits at and below the mobile traverse of on the order of 200m should be surface. While the return of samples from polar sites sufficient to sample the fine-scale diversity of most may result in significant additional science return, we polar terrains. are presently very far from a situation where sample return is to make further scientific progress. Instrumentation: The MPL MVACS payload de- required veloped a number of new experimental approaches Furthermore, because of the significant expense and and technologies that were successfully demonstrated risks associated with sample return, the non-zero in testing. The use of a dexterous, multi-jointed ro- probably of “negative progress” (i.e. mission failure) botic arm to obtain surface and subsurface soil and ice should be a significant factor in the decision making samples within a wide workspace appears to be a very process. When viewed from a larger perspective, the flexible approach that can be adapted to a wide range opportunities and challenges facing future polar of future mission scenarios. The use of Tunable Diode lander missions have a great deal in common with all Laser Spectrometers (TDL) to measure the concentra- Mars missions. tion of water vapor and carbon dioxide gas in the References: [1] Head, J. W. (2000) LPS XXXI. Martian atmosphere, and in evolved gases from heated [2] Smith, D. et al. (2000) LPS XXXI. [3] Parker, T. soil and ice samples is a powerful and robust ap- J., Clifford S. M. and Banerdt, W. B. (2000) LPS proach. Improvements in TDL technology in future XXXI [4] Malin, M. C. and Edgett, K. S. (2000) LPS mission should enable detailed in-situ characteriza- XXXI. [5] Thomas etal. (2000) LPS XXXI. [6] MSSS tions of the isotopic composition of Martian water and Website (http://www.msss.com) carbon-dioxide. The use of a focusable camera mounted on the that can obtain close-up images of the surface and samples is also a very pow-