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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.04.018 Byline: D. Loizeau (a)(b), N. Mangold (c), F. Poulet (a), V. Ansan (c), E. Hauber (d), J.-P. Bibring (a), B. Gondet (a), Y. Langevin (a), P. Masson (b), G. Neukum (e) Keywords: Mars, Surface; Mineralogy; Spectroscopy; Infrared observations Abstract: The Mawrth Vallis region contains an extensive (at least 300kmx400km) and thick ([greater than or equal to]300m), finely layered (at meter scale), clay-rich unit detected by OMEGA. We use OMEGA, HRSC DTMs derived from stereoscopic imagery, HRSC color imagery and high resolution imagery such as MOC, CTX and HiRISE to characterize the geometry and the composition of the clay-rich unit at the regional scale. Our results show that the clay-bearing unit can be divided into sub-units on the basis of differences in color and composition. In false-color visible imagery, alternating white/bluish and orange/red colored units correspond to a compositional succession of, respectively, Al- and Fe- or Mg-phyllosilicate rich material. Geological cross-sections are presented along the principal outcrops of the region in order to define the stratigraphy of these sub-units. This method shows that the dips of the sub-units are frequently close to the slopes of the present topography, except for scarps visible at the dichotomy boundary, inside impact craters walls, and outcrops inside Mawrth Vallis. In addition to the Al- and Fe- or Mg-phyllosilicate rich sub-units, an altered surface is identified as the lower basement unit. We propose two possible end-member scenarios to explain the derived stratigraphy: (1) alteration of volcaniclastic, aeolian or aqueous layered deposits of various compositions by groundwater, resulting in distinct altered rocks; or (2) Alteration coeval with the deposition of sediments under varying chemical conditions, in wet pedodiagenetic environment. Author Affiliation: (a) IAS-UMR8617, Universite Paris-Sud XI, Bat. 121, 91405 Orsay cedex, France (b) IDES-UMR8148, Universite Paris-Sud XI, Bat. 509, 91405 Orsay cedex, France (c) LPGN-UMR6112, Universite de Nantes, 2 rue de la Houssiniere, BP 92208, 44322 Nantes cedex 3, France (d) Institute for Planetary Exploration, DLR, Rutherfordstr. 2, 12489 Berlin, Germany (e) Freie Universitaet Berlin, FR Planetologie und Fernerkundung, Malteserstr. 74-100, 12249 Berlin, Germany Article History: Received 19 August 2008; Revised 10 April 2009; Accepted 14 April 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.03.030 Byline: Horton E. Newsom (a), Nina L. Lanza (a), Ann M. Ollila (a), Sandra M. Wiseman (b), Ted L. Roush (c), Giuseppe A. Marzo (d), Livio L. Tornabene (e), Chris H. Okubo (f), Mikki M. Osterloo (g), Victoria E. Hamilton (h), Larry S. Crumpler (i) Keywords: Mars; Mars, surface; Geologic processes; Cratering Abstract: Morphological features on the western floor of Miyamoto crater in southwestern Meridiani Planum, Mars, are suggestive of past fluvial activity. Imagery from the High Resolution Imaging Science Experiment (HiRISE) gives a detailed view of raised curvilinear features that appear to represent inverted paleochannel deposits. The inverted terrain appears to be capped with a resistant, dark-toned deposit that is partially covered by unconsolidated surficial materials. Subsequent to deposition of the capping layer, erosion of the surrounding material has left the capping materials perched on pedestals of uneroded basal unit material. Neither the capping material nor the surrounding terrains show any unambiguous morphological evidence of volcanism or glaciation. The capping deposit may include unconsolidated or cemented stream deposits analogous to terrestrial inverted channels in the Cedar Mountain Formation near Green River, Utah. In addition to this morphological evidence for fluvial activity, phyllosilicates have been identified in the basal material on the floor of Miyamoto crater by orbital spectroscopy, providing mineralogical evidence of past aqueous activity. Based on both the morphological and mineralogical evidence, Miyamoto crater represents an excellent site for in situ examination and sampling of a potentially habitable environment. Author Affiliation: (a) Department of Earth and Planetary Sciences and Institute of Meteoritics, University of New Mexico, MSC03 2050, 1 University of New Mexico, Albuquerque, NM 87131, USA (b) Department of Earth and Planetary Sciences, Washington University, St. Louis, MO 63130, USA (c) NASA Ames Research Center, Moffett Field, CA 94035-1000, USA (d) NASA Postdoctoral Program Fellow, NASA Ames Research Center, Moffett Field, CA 94035-1000, USA (e) Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721-0063, USA (f) US Geological Survey, Flagstaff, AZ 86001, USA (g) Hawai'i Institute of Geophysics and Planetology, University of Hawai'i at Manoa, Honolulu, HI 96822, USA (h) Southwest Research Institute, Boulder, CO 80302, USA (i) New Mexico Museum of Natural History and Science, Albuquerque, NM 87104, USA Article History: Received 3 November 2008; Revised 3 March 2009; Accepted 6 March 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.05.030 Byline: N. Thomas (a), C.J. Hansen (b), G. Portyankina (a), P.S. Russell (a) Keywords: Mars; Mars, Polar Geology; Mars, Surface Abstract: The High Resolution Imaging Science Experiment (HiRISE) onboard Mars Reconnaissance Orbiter (MRO) has been used to monitor the seasonal evolution of several regions at high southern latitudes and, in particular, the jet-like activity which may result from the process described by Kieffer (JGR, 112, E08005, doi:10.1029/2006JE002816, 2007) involving translucent CO.sub.2 ice. In this work, we mostly concentrate on observations of the Inca City (81[degrees]S, 296[degrees]E) and Manhattan (86[degrees]S, 99[degrees]E) regions in the southern spring of 2007. Two companion papers, [Hansen et al. this issue] and [Portyankina et al. this issue], discuss the surface features in these regions and specific models of the behaviour of CO.sub.2 slab ice, respectively. The observations indicate rapid on-set of activity in late winter initiating before HiRISE can obtain adequately illuminated images (Ls30gs.sup.-1 from a single typical jet feature. Brighter deposits at Inca City become increasingly hard to detect after Ls=210[degrees]. In the Inca City region, the orientations of surficial deposits are topographically controlled. The deposition of dark material also appears to be influenced by local topography suggesting that the ejection from the vents is at low velocity ( Author Affiliation: (a) Physikalisches Institut, Sidlerstr. 5, University of Bern, CH-3012 Bern, Switzerland (b) Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109, USA Article History: Received 4 November 2008; Revised 1 May 2009; Accepted 28 May 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.08.029 Byline: Ganna Portyankina (a), Wojciech J. Markiewicz (b), Nicolas Thomas (a), Candice J. Hansen (c), Moses Milazzo (d) Keywords: Mars; Mars, Polar caps; Ices; Mars, Surface Abstract: Enigmatic surface features, known as 'spiders', found at high southern martian latitudes, are probably caused by sublimation-driven erosion under the seasonal carbon dioxide ice cap. The Mars Reconnaissance Orbiter (MRO) High Resolution Imaging Science Experiment (HiRISE) has imaged this terrain in unprecedented details throughout southern spring. It has been postulated [Kieffer, H.H., Titus, T.N., Mullins, K.F., Christensen, P.R., 2000. J. Geophys. Res. 105, 9653-9700] that translucent CO.sub.2 slab ice traps gas sublimating at the ice surface boundary. Wherever the pressure is released the escaping gas jet entrains loose surface material and carries it to the top of the ice where it is carried downslope and/or downwind and deposited in a fan shape. Here we model two stages of this scenario: first, the cleaning of CO.sub.2 slab ice from dust, and then, the breaking of the slab ice plate under the pressure built below it by subliming ice. Our modeling results and analysis of HiRISE images support the gas jet hypothesis and show that outbursts happen very early in spring. Author Affiliation: (a) Physikalisches Institut, University of Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland (b) Max-Planck Institute for Solar System Research, Max-Planck Strasse 2, D-37191 Katlenburg-Lindau, Germany (c) Jet Propulsion Laboratory/California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA (d) United States Geological Survey, 2255 North Gemini Drive, Flagstaff, AZ 86001, USA Article History: Received 3 November 2008; Revised 29 August 2009; Accepted 31 August 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.04.006 Byline: Marjorie A. Chan (a), Jens Ormo (b), Scott Murchie (c), Chris H. Okubo (d), Goro Komatsu (e), James J. Wray (f), Patrick McGuire (g), James A. McGovern (c) Keywords: Mars; Geological processes; Mineralogy; Image processing; Terrestrial planets Abstract: High Resolution Imaging Science Experiment (HiRISE) imagery and digital elevation models of the Candor Chasma region of Valles Marineris, Mars, reveal prominent and distinctive positive-relief knobs amidst light-toned layers. Three classifications of knobs, Types 1, 2, and 3, are distinguished from a combination of HiRISE and Thermal Emission Imaging System (THEMIS) images based on physical expressions (geometries, spatial relationships), and spectral data from Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). Type 1 knobs are abundant, concentrated, topographically resistant features with their highest frequency in West Candor, which have consistent stratigraphic correlations of the peak altitude (height). These Type 1 knobs could be erosional remnants of a simple dissected terrain, possibly derived from a more continuous, resistant, capping layer of pre-existing material diagenetically altered through recrystallization or cementation. Types 2 and 3 knobs are not linked to a single stratigraphic layer and are generally solitary to isolated, with variable heights. Type 3 are the largest knobs at nearly an order of magnitude larger than Type 1 knobs. The variable sizes and occasional pits on the tops of Type 2 and 3 knobs suggest a different origin, possibly related to more developed erosion, preferential cementation, or textural differences from sediment/water injection or intrusion, or from a buried impact crater. Enhanced color HiRISE images show a brown coloration of the knob peak crests that is attributable to processing and photometric effects; CRISM data do not show any detectable spectral differences between the knobs and the host rock layers, other than albedo. These intriguing knobs hold important clues to deducing relative rock properties, timing of events, and weathering conditions of Mars history. Author Affiliation: (a) Department of Geology and Geophysics, University of Utah, 115 S. 1460 E., Salt Lake City, UT 84112, USA (b) Centro de Astrobiologi'a (CSIC-INTA), Instituto Nacional de Tecnica Aeroespacial, Ctra de Torrejon a Ajalvir, km 4, 28850 Torrejon de Ardoz, Madrid, Spain (c) John Hopkins University/Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, USA (d) US Geological Survey, Flagstaff, AZ 86001, USA (e) International Research School of Planetary Sciences, Universita d'Annunzio, Viale Pindaro 42, 65127 Pescara, Italy (f) Department of Astronomy, Cornell University, Ithaca, NY 14853, USA (g) McDonnell Center for the Space Sciences, Department of Earth and Planetary Sciences, Washington University in St. Louis, St. Louis, MO 63130, USA (h) Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA Article History: Received 31 October 2008; Revised 3 April 2009; Accepted 4 April 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.04.023 Byline: Alfred S. McEwen (a), Maria E. Banks (a), Nicole Baugh (a), Kris Becker (b), Aaron Boyd (a), James W. Bergstrom (c), Ross A. Beyer (d), Edward Bortolini (c), Nathan T. Bridges (e), Shane Byrne (a), Bradford Castalia (a), Frank C. Chuang (f), Larry S. Crumpler (g), Ingrid Daubar (a), Alix K. Davatzes (h), Donald G. Deardorff (d), Alaina DeJong (a), W. Alan Delamere (i), Eldar Noe Dobrea (e), Colin M. Dundas (a), Eric M. Eliason (a), Yisrael Espinoza (a), Audrie Fennema (a), Kathryn E. Fishbaugh (j), Terry Forrester (a), Paul E. Geissler (b), John A. Grant (j), Jennifer L. Griffes (k), John P. Grotzinger (k), Virginia C. Gulick (d), Candice J. Hansen (e), Kenneth E. Herkenhoff (b), Rodney Heyd (a), Windy L. Jaeger (b), Dean Jones (a), Bob Kanefsky (d), Laszlo Keszthelyi (b), Robert King (a), Randolph L. Kirk (b), Kelly J. Kolb (a), Jeffrey Lasco (c), Alexandra Lefort (l), Richard Leis (a), Kevin W. Lewis (k), Sara Martinez-Alonso (m), Sarah Mattson (a), Guy McArthur (a), Michael T. Mellon (m), Joannah M. Metz (k), Moses P. Milazzo (b), Ralph E. Milliken (e), Tahirih Motazedian (a), Chris H. Okubo (b), Albert Ortiz (a), Andrea J. Philippoff (a), Joseph Plassmann (a), Anjani Polit (a), Patrick S. Russell (l), Christian Schaller (a), Mindi L. Searls (m), Timothy Spriggs (a), Steven W. Squyres (n), Steven Tarr (c), Nicolas Thomas (l), Bradley J. Thomson (e)(o), Livio L. Tornabene (a), Charlie Van Houten (c), Circe Verba (b), Catherine M. Weitz (f), James J. Wray (n) Keywords: Mars; surface; Mars; climate; Mars; polar geology; Image processing Abstract: The High Resolution Imaging Science Experiment (HiRISE) on the Mars Reconnaissance Orbiter (MRO) acquired 8terapixels of data in 9137 images of Mars between October 2006 and December 2008, covering [approximately equal to]0.55% of the surface. Images are typically 5-6km wide with 3-color coverage over the central 20% of the swath, and their scales usually range from 25 to 60cm/pixel. Nine hundred and sixty stereo pairs were acquired and more than 50 digital terrain models (DTMs) completed; these data have led to some of the most significant science results. New methods to measure and correct distortions due to pointing jitter facilitate topographic and change-detection studies at sub-meter scales. Recent results address Noachian bedrock stratigraphy, fluvially deposited fans in craters and in or near Valles Marineris, groundwater flow in fractures and porous media, quasi-periodic layering in polar and non-polar deposits, tectonic history of west Candor Chasma, geometry of clay-rich deposits near and within Mawrth Vallis, dynamics of flood lavas in the Cerberus Palus region, evidence for pyroclastic deposits, columnar jointing in lava flows, recent collapse pits, evidence for water in well-preserved impact craters, newly discovered large rayed craters, and glacial and periglacial processes. Of particular interest are ongoing processes such as those driven by the wind, impact cratering, avalanches of dust and/or frost, relatively bright deposits on steep gullied slopes, and the dynamic seasonal processes over polar regions. HiRISE has acquired hundreds of large images of past, present and potential future landing sites and has contributed to scientific and engineering studies of those sites. Warming the focal-plane electronics prior to imaging has mitigated an instrument anomaly that produces bad data under cold operating conditions. Author Affiliation: (a) Lunar and Planetary Lab, University of Arizona, Tucson, AZ 85721, USA (b) U.S. Geological Survey, 2255 N. Gemini Drive, Flagstaff, AZ 86001, USA (c) Ball Aerospace & Technologies Corp., 1600 Commerce St., Boulder, CO 80301, USA (d) NASA Ames Research Center and SETI Institute, Moffett Field, CA 94035, USA (e) Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr., Pasadena, CA 91109, USA (f) Planetary Science Institute, 1700 E. Ft. Lowell, Tucson, AZ 85719, USA (g) New Mexico Museum of Natural History and Science, 1901 Mountain Road NW, Albuquerque, NM 87104, USA (h) Department of Earth and Environmental Science, Temple University, 1901 N. 13th St. Philadelphia, PA 19122, USA (i) Delamere Support Systems, 525 Mapleton Ave., Boulder, CO 80304, USA (j) Smithsonian Institution, National Air and Space Museum, 6th at Independence SW, Washington, DC 20560, USA (k) Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA (l) University of Bern, Sidlerstr. 5, CH-3012 Bern, Switzerland (m) University of Colorado, 392 UCB, Boulder, CO 80309, USA (n) Cornell University, 428 Space Sciences Building, Ithaca, NY 14853, USA (o) Applied Physics Laboratory, Laurel, MD 20723, USA Article History: Received 4 November 2008; Revised 8 April 2009; Accepted 17 April 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.07.021 Byline: C.J. Hansen, N. Thomas, G. Portyankina, A. McEwen, T. Becker, S. Byrne, K. Herkenhoff, H. Kieffer, M. Mellon Keywords: Mars, Polar caps Abstract: The High Resolution Imaging Science Experiment (HiRISE) on the Mars Reconnaissance Orbiter (MRO) has imaged the sublimation of Mars' seasonal CO.sub.2 polar cap with unprecedented detail for one complete martian southern spring. In some areas of the surface, beneath the conformal coating of seasonal ice, radially-organized channels are connected in spidery patterns. The process of formation of this terrain, erosion by gas from subliming seasonal ice, has no earthly analog. The new capabilities (high resolution, color, and stereo images) of HiRISE enable detailed study of this enigmatic terrain. Two sites are analyzed in detail, one within an area expected to have translucent seasonal CO.sub.2 ice, and the other site outside that region. Stereo anaglyphs show that some channels grow larger as they go uphill - implicating gas rather than liquid as the erosive agent. Dark fans of material from the substrate are observed draped over the seasonal ice, and this material collects in thin to thick layers in the channels, possibly choking off gas flow in subsequent years, resulting in inactive crisscrossing shallow channels. In some areas there are very dense networks of channels with similar width and depth, and fewer fans emerging later in the season are observed. Subtle variations in topography affect the channel morphology. A new terminology is proposed for the wide variety of erosional features observed. Author Affiliation: Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr., Pasadena, CA 91109-8099, United States Article History: Received 4 November 2008; Revised 5 June 2009; Accepted 14 July 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.04.011 Byline: Kathryn E. Fishbaugh, Shane Byrne, Kenneth E. Herkenhoff, Randolph L. Kirk, Corey Fortezzo, Patrick S. Russell, Alfred McEwen Keywords: Mars; Polar Geology; Mars; Climate; Mars; Polar Caps Abstract: Using data from the High Resolution Imaging Science Experiment (HiRISE) aboard the Mars Reconnaissance Orbiter, we reassess the methods by which layers within the north polar layered deposits (NPLD) can be delineated and their thicknesses measured. Apparent brightness and morphology alone are insufficient for this task; high resolution topographic data are necessary. From these analyses, we find that the visible appearance of layers depends to a large degree on the distribution of younger, mantling deposits (which in turn is partially influenced by inherent layer properties) and on the shape and location of the particular outcrop. This younger mantle partially obscures layer morphology and brightness and is likely a cause of the gradational contacts between individual layers at this scale. High resolution images reveal that there are several layers similar in appearance to the well-known marker bed discovered by Malin, M., Edgett, K., 2001. J. Geophys. Res. 106, 23429-23570. The morphology, thicknesses (4-8[+ or -]2m), and separation distances (5-32[+ or -]2m) of these marker beds, as gleaned from a high resolution stereo digital elevation model, lend insight into the connection between stratigraphy and climate. Author Affiliation: Smithsonian National Air and Space Museum, Center for Earth and Planetary Studies, P.O. Box 37012, MRC 315, Washington, DC 20013, USA Article History: Received 18 August 2008; Revised 14 February 2009; Accepted 4 April 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.09.011 Byline: W.L. Jaeger (a), L.P. Keszthelyi (a), J.A. Skinner (a), M.P. Milazzo (a), A.S. McEwen (b), T.N. Titus (a), M.R. Rosiek (a), D.M. Galuszka (a), E. Howington-Kraus (a), R.L. Kirk (a) Keywords: Geological processes; Mars, Surface; Volcanism Abstract: Recently acquired data from the High Resolution Imaging Science Experiment (HiRISE), Context (CTX) imager, and Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) onboard the Mars Reconnaissance Orbiter (MRO) spacecraft were used to investigate the emplacement of the youngest flood-lava flow on Mars. Careful mapping finds that the Athabasca Valles flood lava is the product of a single eruption, and it covers 250,000km.sup.2 of western Elysium Planitia with an estimated 5000-7500km.sup.3 of mafic or ultramafic lava. Calculations utilizing topographic data enhanced with MRO observations to refine the dimensions of the channel system show that this flood lava was emplaced turbulently over a period of only a few to several weeks. This is the first well-documented example of a turbulently emplaced flood lava anywhere in the Solar System. However, MRO data suggest that this same process may have operated in a number of martian channel systems. The magnitude and dynamics of these lava floods are similar to the aqueous floods that are generally believed to have eroded the channels, raising the intriguing possibility that mechanical erosion by lava could have played a role in their incision. Author Affiliation: (a) US Geological Survey, 2255 N. Gemini Dr., Flagstaff, AZ 86001, United States (b) Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, United States Article History: Received 14 November 2008; Revised 12 August 2009; Accepted 2 September 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.06.005 Byline: A. Lefort, P.S. Russell, N. Thomas Keywords: Mars, Surface; Geological processes; Ices Abstract: The Peneus and Amphitrites Paterae region of Mars displays large areas of smooth, geologically young terrains overlying a rougher and older topography. These terrains may be remnants of the mid-latitude mantle deposit, which is thought to be composed of ice-rich material originating from airfall deposition during a high-obliquity period less than 5Ma ago. Within these terrains, there are several types of potentially periglacial features. In particular, there are networks of polygonal cracks and scalloped-shaped depressions, which are similar to features found in Utopia Planitia in the northern hemisphere. This area also displays knobby terrain similar to the so-called 'basketball terrains' of the mid and high martian latitudes. We use recent high resolution images from the High Resolution Imaging Science Experiment (HiRISE) along with data from previous Mars missions to study the small-scale morphology of the scalloped terrains, and associated polygon network and knobby terrains. We compare these with the features observed in Utopia Planitia and attempt to determine their formation process. While the two sites share many general features, scallops in Peneus/Amphitrites Paterae lack the diverse polygon network (i.e. there is little variation in the polygon sizes and shapes) and large curvilinear ridges observed in Utopia Planitia. This points to a more homogeneous ice content within the substrate in the Peneus/Amphitrites Paterae region and implies that scallop formation is independent of polygon formation. This work shows that, as in Utopia Planitia, sublimation of interstitial ice is a likely process explaining the formation of the scalloped depressions in the region of Peneus/Amphitrites Paterae. Therefore, we provide a simplified scallop formation model based on sublimation of interstitial ice as proposed for Utopia Planitia. We also show that the differences in scallop morphologies between the two regions may be explained by differences in near-surface ice content, sublimation rates and age of formation of the scalloped terrains. Author Affiliation: Space Research and Planetary Sciences, Physikalisches Institut, Universitat Bern, 3012 Bern, Switzerland Article History: Received 10 October 2008; Revised 15 May 2009; Accepted 3 June 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.07.019 Byline: Jun Nozawa (a), Katsuo Tsukamoto (a), Hidekazu Kobatake (a)(b), Junya Yamada (a), Hisao Satoh (a)(c), Ken Nagashima (a)(d), Hitoshi Miura (a), Yuki Kimura (a) Keywords: Meteorites; Solar nebula; Interplanetary dust Abstract: By means of nanoscale surface observation, we have proposed a new approach for investigating fine crystals of cosmic materials to reveal their origin and growth conditions. Several different morphologies of polyhedral fine olivines with faceted faces have been found in Allende carbonaceous chondrite (4.5byr in geochronological age). In the present work, molecular level topography of the faceted matrix olivine by Atomic Force Microscopy (AFM) has successfully been performed. The matrix olivine found to have preserved growth step pattern on its surface even though quite long time has passed since they formed in the early Solar System. The surface pattern suggests that the faceted matrix olivine could have been condensed from the gas phase, and possibly that these olivine crystals had continued to grow under a rapid cooling condition (0.1-1Ks.sup.-1). The estimated cooling rate agrees well with predictions based on hypothetical rapid heating and cooling events such as shock wave heating. Author Affiliation: (a) Department of Earth and Planetary Materials Science, Graduate School of Science, Tohoku University, 6-3 Aramaki Aza-Aoba, Aoba-ku, Sendai 980-8578, Japan (b) Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan (c) SERNUC Corporation, Mitsubishi Materials Corporation, 1-297, Kitabukuro, Omiya-ku, Saitama 330-0835, Japan (d) Division of Electrical, Electronic and Information Engineering, Graduate School of Engineering, Osaka University, 2-1 Yamada-Oka, Suita 565-0871, Japan Article History: Received 11 January 2008; Revised 16 June 2009; Accepted 1 July 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.07.033 Byline: Laurence A. Soderblom (a), Robert H. Brown (b), Jason M. Soderblom (b), Jason W. Barnes (c), Randolph L. Kirk (a), Christophe Sotin (d), Ralf Jaumann (e)(f), David J. Mackinnon (a), Daniel W. Mackowski (g), Kevin H. Baines (d), Bonnie J. Buratti (d), Roger N. Clark (h), Philip D. Nicholson (i) Keywords: Saturn; Titan; Geological processes Abstract: Joint Cassini VIMS and RADAR SAR data of [approximately equal to]700-km-wide Hotei Regio reveal a rich collection of geological features that correlate between the two sets of images. The degree of correlation is greater than anywhere else seen on Titan. Central to Hotei Regio is a basin filled with cryovolcanic flows that are anomalously bright in VIMS data (in particular at 5[mu]m) and quite variable in roughness in SAR. The edges of the flows are dark in SAR data and appear to overrun a VIMS-bright substrate. SAR-stereo topography shows the flows to be viscous, 100-200m thick. On its southern edge the basin is ringed by higher ([approximately equal to]1km) mountainous terrain. The mountains show mixed texture in SAR data: some regions are extremely rough, exhibit low and spectrally neutral albedo in VIMS data and may be partly coated with darker hydrocarbons. Around the southern margin of Hotei Regio, the SAR image shows several large, dendritic, radar-bright channels that flow down from the mountainous terrain and terminate in dark blue patches, seen in VIMS images, whose infrared color is consistent with enrichment in water ice. The patches are in depressions that we interpret to be filled with fluvial deposits eroded and transported by liquid methane in the channels. In the VIMS images the dark blue patches are encased in a latticework of lighter bands that we suggest to demark a set of circumferential and radial fault systems bounding structural depressions. Conceivably the circular features are tectonic structures that are remnant from an ancient impact structure. We suggest that impact-generated structures may have simply served as zones of weakness; no direct causal connection, such as impact-induced volcanism, is implied. We also speculate that two large dark features lying on the northern margin of Hotei Regio could be calderas. In summary the preservation of such a broad suite of VIMS infrared color variations and the detailed correlation with features in the SAR image and SAR topography evidence a complex set of geological processes (pluvial, fluvial, tectonic, cryovolcanic, impact) that have likely remained active up to very recent geological time ( Author Affiliation: (a) United States Geological Survey, 2255 N Gemini Dr, Flagstaff, AZ, USA (b) Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA (c) Dept. of Physics, University of Idaho, Moscow, ID, USA (d) Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA (e) DLR, Institute of Planetary Research, Berlin, Germany (f) Dept. of Earth Sciences, Inst. of Geosciences, Freie Universitat, Berlin, Germany (g) Dept. of Mechanical Engineering, Auburn University, Auburn, AL, USA (h) United States Geological Survey, Denver, CO, USA (i) Astronomy Dept., Cornell University, Ithaca, NY, USA Article History: Received 14 April 2009; Revised 21 July 2009; Accepted 22 July 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.05.032 Byline: Ian Garrick-Bethell, Maria T. Zuber Keywords: Moon Abstract: The South Pole-Aitken basin (SP-A) is the largest and oldest basin on the Moon. The basin has usually been interpreted to exhibit a degraded circular structure, but here we demonstrate that the topography, iron and thorium signatures of the basin are well described by ellipses with axes measuring 2400 by 2050km and centered at -53[degrees], 191[degrees]E. Topography, abundances of iron, thorium, and the distribution of mare basalts are all elevated in the northern halves of the ellipses. We also identify an outer topographic ellipse whose semiminor axis scales with the main topographic ellipse by approximately 2. Taken together, these data imply that the basin was created by an oblique impact along an azimuth of approximately 19[degrees], measured counterclockwise from longitude 191[degrees]E. The geometry of the elevated central farside topography surrounding SP-A suggests that it predates the impact. The elliptical ring structures of SP-A and their scaling relationships will help to understand the formation of large and elliptical basins elsewhere in the Solar System. This refined basin shape will also inform local geology, geochemistry, and geophysics of the region. Author Affiliation: Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 54-521, 77 Massachusetts Avenue, Cambridge, MA 02139, United States Article History: Received 5 June 2008; Revised 12 May 2009; Accepted 15 May 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.04.026 Byline: Tomasz F. Stepinski (a), Michael P. Mendenhall (b), Brian D. Bue (c) Keywords: Cratering; Mars; Surface Abstract: This study presents an automated system for cataloging impact craters using the MOLA 128pixels/degree digital elevation model of Mars. Craters are detected by a two-step algorithm that first identifies round and symmetric topographic depressions as crater candidates and then selects craters using a machine-learning technique. The system is robust with respect to surface types; craters are identified with similar accuracy from all different types of martian surfaces without adjusting input parameters. By using a large training set in its final selection step, the system produces virtually no false detections. Finally, the system provides a seamless integration of crater detection with its characterization. Of particular interest is the ability of our algorithm to calculate crater depths. The system is described and its application is demonstrated on eight large sites representing all major types of martian surfaces. An evaluation of its performance and prospects for its utilization for global surveys are given by means of detailed comparison of obtained results to the manually-derived Catalog of Large Martian Impact Craters. We use the results from the test sites to construct local depth-diameter relationships based on a large number of craters. In general, obtained relationships are in agreement with what was inferred on the basis of manual measurements. However, we have found that, in Terra Cimmeria, the depth/diameter ratio has an abrupt decrease at [approximately equal to]38[degrees]S regardless of crater size. If shallowing of craters is attributed to presence of sub-surface ice, a sudden change in its spatial distribution is suggested by our findings. Author Affiliation: (a) Lunar and Planetary Institute, 3600 Bay Area Blvd., Houston, TX 77058, USA (b) Department of Physics 103-33, Caltech, Pasadena, CA 91125, USA (c) Jet Propultion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109, USA Article History: Received 21 March 2007; Revised 31 March 2009; Accepted 2 April 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.03.003 Byline: Thomas S. Statler Keywords: Asteroids; dynamics; Asteroids; rotation; Asteroids; surfaces; Near-Earth objects Abstract: Radiation recoil (YORP) torques are shown to be extremely sensitive to small-scale surface topography, using numerical simulations. Starting from a set of 'base objects' representative of the near-Earth object population, random realizations of three types of small-scale topography are added: Gaussian surface fluctuations, craters, and boulders. For each, the expected relative errors in the spin and obliquity components of the YORP torque caused by the observationally unresolved small-scale topography are computed. Gaussian power, at angular scales below an observational limit, produces expected errors of order 100% if observations constrain the surface to a spherical harmonic order l[less than or approximately equal to]10. For errors under 10%, the surface must be constrained to at least l=20. A single crater with diameter roughly half the object's mean radius, placed at random locations, results in expected errors of several tens of percent. The errors scale with crater diameter D as D.sup.2 for D0.3 and as D.sup.3 for D Author Affiliation: Astrophysical Institute, Department of Physics and Astronomy, 251B Clippinger Research Laboratories, Ohio University, Athens, OH 45701, USA Article History: Received 6 January 2009; Revised 16 February 2009; Accepted 2 March 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.03.031 Byline: Joshua L. Bandfield Keywords: Mars; surface; Spectroscopy; Radiative transfer Abstract: Slopes are present in martian apparent surface emissivity observations collected by the Thermal Emission Spectrometer (TES) and the Thermal Emission Imaging System (THEMIS). These slopes are attributed to misrepresenting the surface temperature, either through incorrect assumptions about the maximum emissivity of surface materials or the presumption of a uniform surface temperature within the field of view. These incorrect assumptions leave distinct characteristics in the resulting apparent emissivity data that can be used to gain a better understanding of the surface properties. Surfaces with steep slopes typically have a variable surface temperatures within the field of view that cause distinct and highly variable slopes in apparent emissivity spectra based on the observing conditions. These properties are documented on the southwestern flank of Apollinaris Patera and can be reasonably approximated by modeled data. This spectral behavior is associated with extremely rough martian surfaces and includes surfaces south of Arsia Mons and near Warrego Valles that also appear to have high slopes in high resolution images. Surfaces with low maximum values of emissivity have apparent emissivity spectra with more consistent spectral slopes that do not vary greatly based on observing conditions. This spectral surface type is documented in Terra Serenum and is consistent with associated high resolution images that do not indicate the presence of a surface significantly rougher that the surrounding terrain. Author Affiliation: Department of Earth and Space Sciences, University of Washington, Seattle, WA 98195-1310, USA Article History: Received 29 December 2008; Revised 20 March 2009; Accepted 23 March 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.02.025 Byline: Gareth A. Morgan, James W. Head Keywords: Mars; surface Abstract: The majority of martian valley networks are found on Noachian-aged terrain and are attributed to be the result of a 'warm and wet' climate that prevailed early in Mars' history. Younger valleys have been identified, though these are largely interpreted to be the result of localized conditions associated with the melting of ice from endogenic heat sources. Sinton crater, a 60 km diameter impact basin in the Deuteronilus Mensae region of the dichotomy boundary, is characterized by small anastomosing valley networks that are located radial to the crater rim. Large scale deposits, interpreted to be the remains of debris covered glaciers, have been identified in the area surrounding Sinton, and our observations have revealed the occurrence of an ice rich fill deposit within the crater itself. We have conducted a detailed investigated into the Sinton valley networks with all the available remote data sets and have dated their formation to the Amazonian/Hesperian boundary. The spatial and temporal association between Sinton crater and the valley networks suggest that the impact was responsible for their formation. We find that the energy provided by an asteroid impact into surficial deposits of snow/ice is sufficient to generate the required volumes of melt water needed for the valley formation. We therefore interpret these valleys to represent a distinct class of martian valley networks. This example demonstrates the potential for impacts to cause the onset of fluvial erosion on Mars. Our results also suggest that periods of glacial activity occurred throughout the Amazonian and into the Hesperian in association with variations in spin orbital parameters. Author Affiliation: Department of Geological Sciences, Brown University, 324 Brook Street, Providence, RI 02912, USA Article History: Received 19 December 2007; Revised 3 November 2008; Accepted 9 February 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2008.10.023 Byline: Howard A. Zebker (a), Yonggyu Gim (b), Philip Callahan (b), Scott Hensley (b), Ralph Lorenz (c) Keywords: Titan; Satellites; surfaces; Radar observations; Instrumentation Abstract: The Cassini spacecraft has acquired 25 radar altimeter elevation profiles along Titan's surface as of April 2008, and we have analyzed 18 of these for which there are currently reconstructed ephemeris data. Altimeter measurements were collected at spatial footprint sizes from 6-60 km along ground tracks of length 400-3600 km. The elevation profiles yield topographic information at this resolution with a statistical height accuracy of 35-50 m and kilometer-scale errors several times greater. The data exhibit significant variations in terrain, from flat regions with little topographic expression to very rugged Titanscapes. The bandwidth of the transmitted waveform admits vertical resolution of the terrain height to 35 m at each observed location on the surface. Variations in antenna pointing and changes in surface statistics cause the range-compressed radar echoes to exhibit strong systematic and time-variable biases of hundreds of meters in delay. It is necessary to correct the received echoes for these changes, and we have derived correction algorithms such that the derived echo profiles are accurate at the 100 m level for off-nadir pointing errors of 0.3[degrees] and 0.6[degrees], for leading edge and echo centroid estimators, respectively. The leading edge of the echo yields the elevation of the highest points on the surface, which we take to be the peaks of any terrain variation. The mean value of the echo delay is more representative of the mean elevation, so that the difference of these values gives an estimate of any local mountain heights. Finding locations where these values diverge indicates higher-relief terrain. Elevation features are readily seen in the height profiles. Several of the passes show mountains of several hundred m altitude, spread over 10's or even 100's of km in spatial extent, so that slopes are very small. Large expanses of sub-100 m topography are commonplace on Titan, so it is rather smooth in many locations. Other areas exhibit more relief, although the overall observed variation in surface height on any pass is less than about 1 km. Some elevation features correspond to observed changes in brightness in Cassini infrared images, but many do not. Correspondence between the imaging SAR ground tracks and the altimeter paths is limited, so that identifying elevation changes with higher resolution SAR features is premature at present. Author Affiliation: (a) Departments of Geophysics and Electrical Engineering, 360 Mitchell Building, MC 2215, 397 Panama Mall, Stanford University, Stanford, CA 94305-2215, USA (b) Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA (c) Johns Hopkins University Applied Physics Lab, Laurel, MD 20723, USA (d) Cassini Project, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA Article History: Received 21 May 2008; Revised 22 September 2008; Accepted 31 October 2008

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2008.09.021 Byline: Takeshi Imamura (a), Hiroko Kobayashi (b) Keywords: Atmospheres; dynamics; Mars; atmosphere Abstract: Wavenumber spectra of the martian atmosphere covering zonal wavenumbers s=1-6 were obtained as a function of latitude and season for the first time from the temperatures measured by the Thermal Emission Spectrometer onboard the Mars Global Surveyor. The stationary component tends to peak at s=2, where the martian topography has large amplitude, and drops rapidly at higher wavenumbers. The transient component in the middle and high latitudes tends to peak at s=1, which is lower than the most unstable wavenumber based on linear theories, and exhibits spectral slopes much flatter than the stationary component. In the equatorial region, the spectra of the transient component are almost flat, indicating that the organization of large-scale structures is less efficient in this region. The spectral shapes are similar between the 0.5 and 2.2 hPa surfaces, except that the slopes are slightly steeper at 0.5 than at 2.2 hPa, probably due to selective vertical transmission at low wavenumbers. The seasonal variation is relatively large in the middle and high latitudes, where the maximum power occurs in winter and the minimum occurs in summer, with an exception that the transient component is maximum in spring in the southern hemisphere. Intensification of s=1 transient waves is observed around the period of the initiation of global dust storms. Author Affiliation: (a) Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Sagamihara 229-8510, Japan (b) NEC Aerospace Systems, Ltd., 1-10 Nisshin-cho, Fuchu 183-8501, Japan Article History: Received 7 July 2008; Revised 14 September 2008; Accepted 20 September 2008