Workshop on Role of Volatiles and Atmospheres on Martian Impact Craters 77

CHARACTERISTICS OF IMPACT CRATERS AND INTERIOR DEPOSITS: ANALYSIS OF THE SPATIAL AND TEMPORAL DISTRIBUTION OF VOLATILES IN THE HIGHLANDS OF MARS. S.C. Mest, Planetary Geodynamics Laboratory (Code 698), NASA Goddard Space Flight Center, Bldg. 33, Rm. F320, Greenbelt, MD 21071, mest~kclsei.csfc.nc?sa.cov.

Introduction: The martian southern highlands contain will be used to produce detailed geologic and impact craters that display pristine to degraded geomorphic maps of individual impact craters, morphologies, and preserve a record of degradation especially those containing enigmatic deposits, as well that can be attributed to fluvial, eolian, mass wasting, as maps at local and regional scales. Individual craters, volcanic and impact-related processes. However, the such as Terby, Rabe, Proctor, Schaeberle, Schroeter, relative degree of modification by these processes and Martz, Gale and several unnamed craters, that are well- the amounts of material contributed to crater interiors covered Mars data, will be mapped in detail. Mapping are not well constrained. could determine if similar degradation styles were Impact craters (D>10 km) within Terra Cimmeria common, such as by precipitation-driven processes or (0”-6O”S, 19Oo-24O0W), Terra Tyrrhena (Oo-3O0S, by a regional mantling unit [5,6] that contributes 260”-3 lOoW) and Noachis Terra (2O”-5O0S, 310”- material to crater floors via mass wasting, or differ 340”W) are being examined to better understand the from crater to crater, suggesting mostly localized degradational history and evolution of highland processes were (are) active. Relative age relationships terrains. The following scientific objectives will be for crater interior deposits will be determined by accomplished. 1) Determine the geologic processes that calculating crater size-frequency distribution statistics. modified impact craters (and surrounding highland terrains). 2) Determine the sources (e.g. fluvial, Observations: Extensive evidence that fluvial, mass lacustrine, eolian, mass wasting, volcanic, impact melt) wasting, eolian, volcanic and impact-related processes and relative amounts of material composing crater were involved in degradation, infilling and subsequent interior deposits. 3) Document the relationships erosion of impact craters are preserved in the highlands between impact crater degradation and highland fluvial of Noachis Terra, Tyrrhena Terra and Terra Cimmeria. systems. 4) Determine the spatial and temporal Fluvial systems dissect large parts of these relationships between degradational processes on local highland terrains; their tributaries erode crater rim and and regional scales. And 5) develop models of impact ejecta materials and breach the rims of some craters. crater (and highland) degradation that can be applied to The interior walls of many craters are incised with these and other areas of the martian highlands. The gullies. Some gullies head at or near crater rims, results of this study will be used to constrain the suggesting erosion by precipitation-derived runoff [ 1,?- geologic, hydrologic and climatic evolution of Mars IO], whereas other gullies originate at discrete layers and identify environments in which subsurface water along crater walls 1 L I]. Some craters contain small might be present or evidence for biologic activity valley networks along their rims, which resulted in might be preserved. emplacement of alluvial fans [I 2,131 on their floors. The presence of these features suggests fluvial Methodology: This research utilizes multiple data sets processes were a key factor in crater degradation. to accomplish the objectives stated above. Images Many highland craters contain lobate debris aprons (Viking Orbiter, MOC, and THEMIS vis and IR (day)) (Late Hesperian to Amazonian) that extend onto their are being analyzed to characterize (a) the preservation floors, suggesting volatile-driven mass wasting also states (e.g., “fresh”, “degraded”, “moderately actively modified crater interiors and contributed degraded”, “highly degraded”, and “buried” or significant amounts of material to crater floors. Mass “exhumed” [ 1-31) and (b) interior deposits of craters. wasting may have been an equally important process of MOLA data and the IDL module GRIDVIEW [41 are crater degradation, especially in the highlands northeast being used to estimate morphometric parameters for and east of Hellas basin [ 13- I 81 where volatiles appear craters (e.g., diameter, depth, slopes), regional and to have been abundant, and less important in other local slopes, and thicknesses and volumes of crater areas where volatiles may have been spatially or interior deposits. THEMIS infrared images and TES temporally less abundant [ 7-9. IO]. data are being used to characterize surface properties Dune fields and dark splotches within craters, such (e.& emission. roughness) of crater interior deposits, as Rabe and Proctor [191, indicate eolian processes and the Mars Observer GRS is being used to observe may contribute, or at least redistribute, significant the distribution of surficial hydrogen. These data sets quantities of sediments to interior deposits 1‘7-1 01. I8 LPI Contribution No. 1273

Many craters could also contain materials materials) and (or) the processes of emplacement and deposited within lacustrine or playa environments. subsequent modification were widespread. It is the Morphologic evidence - inflow and outlet valleys, ongoing goal of this research to use all available Mars layered deposits, deltas, sedimentary terraces, and data to identify deposits associated with specific source shorelines - suggests some martian craters may have areas and determine the process(es) of their erosion and contained lakes 19. I0,1-0-251. emplacement, quantify crater interior deposits (i.e., Several craters, such as Millochau [Q], Terby [26- thickness, volume), and correlate crater degradation 183, Schaeberle, Schroeter and several large unnamed processes locally and regionally to spatially and craters [ 9,29.301, contain enigmatic interior deposits temporally constrain volatile distribution as well as relative to nearby craters of similar size or age. Some assess climate change on Mars. deposits are layered and form plateaus that stand hundreds of meters above surrounding floor materials References: [I! Craddock R.A and A.D. Howard or in some cases are topographically higher than the (2002)JGR, 10 , doi:10.1029/2001JEOO1505. 121 Frey H.V. et al. LPSXEU, Abs. tl . [7] Barlow crater’s rim, such as Gale [>I]. Many craters also (2000) N.G. (2003) Sixth Znt. Conf: on Mars, Abs. 3 . contain pits, suggesting collapse of volatile-rich [4] Roark J.H. et al., (2000) LPS x7w,Abs. PO6 . material, and (or) they contain deposits that display 151 Milliken R.E. and J.F. Mustard (2003) Sixth Znt. surfaces that have been modified more significantly Con$ on Mars, Abs. #@ . [61 Mustard J.F. et al. than nearby craters of similar size and age. (2003) LPS XEUZZ, Abs. #2B . [-I Grant J.A. and Several impact craters north and west of Hellas P.H. Schultz (1993) JGR, B , 11025-11042.[8] Grant basin contain surface materials that display similar J.A. (1999) Znternatl. J. of Impact Eng., 23, 331-340. 19) Mest S.C. and D.A. Crown kurus, surface textures. One deposit in particular, ‘rugged (2005) doi:10.1016/j.icarus.2004.12.008,in press. [I 01 Mest material’ mapped in Millochau 19 1, displays a ‘stucco- S.C. and D.A. Crown (2005) Geol. Map of MTM - like’ surface texture, is typically found along the outer 202 72 and -252 72 Quadrangles, Tyrrhena Terra edges of the crater interior and generally slopes down Region of Mars, U.S.G.S., in review. I 11 1 Malin M.C. from the crater wall toward its center. The and K.S. Edgett (2000) Science, 28 , 2330-2335. characteristics of this unit, combined with the fact that [ 121 Howard A.D. and J.M. Moore (2004) LPS XXn: it is usually found in craters with gullied interior walls, Abs. t19 . [ 131 Moore J.M. and A.D. Howard (2004) LPS XUXV, Abs. . [ 1-11 Crown D.A. et al. suggest it may consist of heavily degraded fluvial #a (1 992) kurus, 10 , 1-25. [I’J Mest S.C. and D.A. Crown deposits and (or) mass wasted materials. Similarly, the (2001) Zcarus, 15 , 89-110.[lhJ Mest S.C. and D.A. surfaces of many plateaus and massifs that compose Crown (2002) Geol. Map of MTM -40252 and -40257 enigmatic crater deposits are generally similar in Quadrangles, ReuN VaNk Region of Mars, U.S.G.S. appearance to the ‘pitted material’ observed in Geol. Invest. Ser. Map 1-2730,scale 1:lM.[17] Mest Millochau [9]. S.C. and D.A. Crown (2003) Geol. Map of MTM - 45252 and -45257 Quadrangles, Reull Vallis Region of Mars, U.S.G.S. Geol. Invest. Ser. Map scale Discussion: Many highland impact craters exhibit 1-2763, 1:lM.[I81 Pierce T.L. and D.A. Crown (2003) kurus, evidence that they were modified (eroded and infilled) 16 , 46-65, doi: 10.1 01 6/S0019-1035(03)00046-0. to various degrees by multiple geologic processes. The [I91 Fenton L.K. et al. (2003) JGR, 18 , doi:10.1029- morphologies of most craters and the deposits 2002JE002015. 1201 Newsom H.E. et al. (1996) JGR, preserved on their floors suggest significant quantities 10 , 14951-14955. I211 Grin E.A. and N.A. Cabrol of volatiles were involved, either atmospherically- (1997) kurus, 19 , 461-474. [211 Forsythe R.D. and derived and (or) released from the subsurface. C.R. Blackwelder (1998) JGR, 19 , 31421-31431. [2?] Cabrol N.A. and E.A. Gnn kurus, la , However, the nature of the processes varies spatially (1999) 160-172. [211 Cabrol N.A. and E.A. Grin (2001) and temporally across relatively short distances (1 00’s kurus, 1!l , 291-328.[E] Grant J.A. and T.J. Parker of kilometers) of the highlands. For example, (2002) JGR, 10 , doi: 10.1029/2001-JE001678. Promethei Terra (east of Hellas basin) displays large 1261 Ansan V. and N. Mangold (2004) Znd Conf on relatively young debris aprons, small Hesperian-aged Early Mars, Abs. 1 . 12-1 Howard A.D. et al. valley networks, and large outflow systems [fq-lg], (2004) Td Conf on Early Mars, Abs. 13 . whereas adjacent Tyrrhena Terra (north of Hellas [X]Wilson, S.A. and A.D. Howard (2005) LPS Abs. PB . [ZQ] Korteniemi, J. et al. basin) is dissected by extensive Noachian-aged valley =Z, (2005) LPS XKWZ, Abs. t8 . [?O] Moore J.M. and A.D. networks, contains enigmatic crater interior deposits, Howard (2005) LPS XXXVI, Abs. t52 . [311 Edgett and lacks debris aprons [9.10]. In addition, craters that K.S. and M.C. Malin (2001)LPSXKXTZ, Abs. b6 . contain similar features (pits, plateaus, etc.) and (or) deposits similar in appearance suggest either emplacement of similar materials (and sequences of