P32B-01
MRO Imaging of the Candidate Landing Sites for the Mars Science Laboratory
The Mars Reconnaissance Orbiter (MRO) spacecraft has obtained more than 110 HiRISE images and comparable numbers of CRISM and CTX images of the more than 50 landing sites proposed for the Mars Science Laboratory (MSL). Many of these images targeted the 20 km by 25 km landing ellipses proposed for the final seven sites under consideration that include Holden crater (26.4S, 325.1E), Eberswalde crater (23.9S, 326.7E), Gale crater (4.5S, 137.4E), Mawrth Vallis (24.7N, 340.1E), Miyamoto crater (3.3S, 352.3E), Nili Fossae trough (21.0N, 74.5E), and South Meridiani (3.3S, 354.4E). MRO data reveal unprecedented morphologic and compositional detail at each site that helps constrain past depositional environments. For example, HiRISE, CRISM, and CTX images reveal laterally extensive, sub- meter and phyllosilicate-bearing stratigraphy in Holden crater indicative of emplacement in a distal alluvial and/or lacustrine setting. In Eberswalde, the distribution and orientation of phyllosilicate-bearing beds appears consistent with past presence of a long-lived fluvial-deltaic system. Gale crater exposes a thick sequence of finely-bedded deposits with phyllosilicate-bearing rocks beneath sulfate-bearing rocks that may incorporate eolian bedforms and displays evidence for local fluvial modification. Mawrth displays an especially diverse stratigraphy of Mg-Fe smectites and Al-rich phyllosilicates whose orientation and extent reflects responsible depositional process. The floor of Miyamoto crater reveals a stripped surface exposing ancient phyllosilicate-bearing materials that were possibly emplaced in an ancient fluvial setting. Nili Fossae trough preserves Noachian stratigraphy, with unaltered basement in contact with diverse phyllosilicate- bearing rocks that may correspond to aqueously altered ejecta from nearby Isidis basin or other altered crustal materials. Finally, South Meridiani includes hematite-bearing, sulfate-rich evaporite sediments that unconformably overlie ancient polygonally fractured, phyllosilicate-bearing and incised bedrock. These seven sites highlight the capabilities of the MRO instruments to detail diverse mineralogy and geomorphologic attributes that characterized ancient Mars and represent compelling aqueous and possibly habitable environments for in situ exploration by MSL.
P32B-02
Sublacustrine Depositional Fans in Melas Chasma
Evidence for ancient lakes on Mars is based on multiple criteria, one of which is the observation of sedimentary deposits that could have formed only in fully submerged settings. Using CTX and HiRISE images, we identify a sublacustrine fan complex on the floor of Southern Melas Basin based on its morphologic similarity to the Mississippi submarine fan complex. Recognition of the fans supports earlier suggestions for the presence of a former lake in Southern Melas Basin based on topographic evidence for a closed basin and the presence of stratigraphic clinoforms interpreted as a subaqueous deposit. The former presence of water in the area is also supported by CRISM reflectance spectra that indicate the presence of opaline silica and other hydrated phases. Southern Melas Basin could represent a complete erosional-to-depositional system, from the fluvially-incised source region in the surrounding highlands to the terminal sediment sink in the topographically lowest part of the basin that hosts the fan deposits. The presence of sublacustrine fans in Melas Chasma indicates that a significant body of water was present and stable at the surface of Mars for at least 100 to 10000 years.
P32B-03
Spectral and Geomorphic Evidence for a Past Inland Sea in Eridania Basin, Mars
Eridania basin is the name given to a depression in the southern highlands composed of many overlapping and highly degraded craters. It is located at the head of Ma"adim Vallis, and has been suggested by [1] to have contained its source waters. Geomorphic evidence presented in [1] for the presence of a paleosea includes 1) the origin of Ma"adim as a fully developed channel at the divide between it and Eridania basin; 2) the floor materials of the six largest craters that form Eridania Basin have an unusually high internal relief (~1 km) and slope (~0.5-1.5°) among degraded Martian craters, which are usually flat-floored; 3) fluvial valleys do not dissect the slopes of these deeper crater floor depressions, unlike similar slopes that are dissected at higher levels in the watershed. Additionally, we identify inward-facing escarpments that extend over large distances at near- constant topographic contours. CRISM Full Resolution Targeted (FRT) observations of outcrop units throughout the region show a preponderance of hydrous mineralogies, including Fe/Mg smectites (identified by 1.4, 1.9, and ~2.3 μm bands), hydrated silica (identified by 1.4, 1.9, and broad 2.2 μm bands), and kaolinite-group (identified primarily by at 1.4 μm band and a doublet at 2.2 μm) minerals. Focused spectral studies of the chaos units found in the three deepest portions of Eridania Basin (Ariadness Colles, Gorgonum Chaos, and Atlantis Chaos) show abundant hydrous minerals associated with the chaos hummocks, suggesting that these hummocks are the erosional remnants of a unit containing aqueously deposited minerals. The distribution of these minerals is found to vary spatially from hummock to hummock and they typically lack obvious bedding at HiRISE scales (50 cm/pixel). Analyses of other geomorphologically distinct indurated units in the region show that Fe/Mg-smectites are present in a large fraction of these units, suggesting a complex history of deposition, alteration, and erosion throughout the region. These materials appear distinct from layered deposits on surrounding surfaces in the Electris region In general, the hydrate-bearing outcrops are being exhumed from under a darker, more resistant mantling unit whose morphology and texture are reminiscent of those observed in the western Arabia Terra region, suggesting that similar geological processes may have been responsible for the deposition of the overlying unit. [1] Irwin, R.P. et al, JGR 109, E12009, 2004.
P32B-04
Martian gullies as seen by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM)
Over 100 high resolution targeted images of martian gullies and debris fans have been obtained by the CRISM instrument currently orbiting Mars aboard the Mars Reconnaissance Orbiter. A survey of these images provides some new constraints on the origin and evolution of these features. We have found no evidence for the recent formation of hydrated minerals in these features, even the most recent light-toned ones. Ice clouds are sometimes visible in the vicinity of the gullies, but these are seasonal. A wide range of mineralogies is observed and includes phyllosilicates, mafics and sulphates. The distribution of the minerals and their relationship to the underlying rocks suggest that the gully-forming process exposes underlying rocks and moves them downslope. When more than one gully is present on a given slope, both vertical and horizontal stratigraphy within the source region is revealed. The wispy nature of the deposits, especially when specific spectral indicators are examined, suggests that the gullies are the result of many small events. The lack of dust coverage on some of the spectrally distinct gullies could indicate fairly recent activity, although eolian erosion could also be a factor. Many other gullies that are indistinct spectrally from their surroundings could be old and inactive, or could indicate very active dust deposition. The processes dominating the modification of the gullies can be established by combining CRISM observations with other nearby geomorphic indicators.
P32B-05
HiRISE Observations of the Polar Regions of Mars
Digital elevation models (DEMs) derived from MRO HiRISE stereo images allow meter-scale topographic measurements in the north polar layered deposits (NPLD) and distinction of slope vs. albedo effects on apparent brightness of individual layers. HiRISE images do not show thin layers at the limit of resolution. Rather, fine layering, if it exists, appears to have been obscured by a more dust-rich mantling deposit which shows signs of eolian erosion and slumping. Stratigraphic sequences within the NPLD appear to be repeated within exposures observed by HiRISE, indicative of a record of periodic climate changes. Granular flows sourced from within the dark, basal unit are suggestive of, but do not require, the presence of water during their formation. Active mass wasting of frost and dust has been observed on steep NPLD scarps in early spring, similar to dry, loose snow avalanches on terrestrial slopes. Bright and dark streaks are seen to evolve during the northern summer, evidence for active eolian redistribution of frost and perhaps dark (non- volatile) material. Relatively dark reddish patches observed within the north polar residual cap during the summer indicate that the cap is very thin (<1 m) or more transparent in places. HiRISE images of exposures of the south polar layered deposits (SPLD) show rectilinear fractures that are continuous across several layers and whose orientation is not affected by the topography of the exposure, suggesting that they were formed before erosion of the SPLD. They appear to extend laterally and vertically through the SPLD, like a joint set. While NPLD tectonism appears limited to isolated grabens, several faults have been observed by HiRISE in the SPLD, showing structural details including reverse fault splays that merge into bedding planes and possible evidence for thrust duplication. The faults may be the result of basal sliding (decollements) ramping into thrust faults near the margin of the SPLD.
P32B-06
Radar Detection of a Subsurface Horizon at the Phoenix Landing Site
Results from the Mars Reconnaissance Orbiter (MRO) Shallow Radar (SHARAD) instrument indicate the presence of a subsurface interface in the Phoenix Landing Site region. In an effort to characterize the site prior to landing, numerous SHARAD observations were made over the Phoenix landing ellipse and the surrounding region. While our initial analysis of these observations did not show clear evidence of subsurface returns, refinement of data processing techniques has allowed us to see an apparent subsurface discontinuity which extends throughout much of the topographic depression known as "Green Valley" in which the lander resides. Coincidentally, the Phoenix spacecraft landed in the area of greatest confidence for this subsurface detection. We will present a series of SHARAD radar observations showing the nature and extent of the detected interface and will discuss how it may be related to observations of the surface from the lander and from other orbiting instruments. It should be noted that SHARAD depth resolution is ~ 8 meters and is not sufficient to resolve the unit that Phoenix's instruments are investigating. However, the shallow surface composition and geometry is encoded in the radar surface echoes. The SHARAD instrument, provided by the Italian Space Agency (ASI) to NASA's MRO mission, is a wide-band (15Ð25 MHz), nadir-looking radar that provides surface altimetry and subsurface structure, the latter in areas where the radar wave penetrates the surface and is reflected from a dielectric discontinuity. SHARAD operates at a center frequency of 20 MHz, has a compositionally dependent depth resolution of ~5--10 m, and a footprint of ~1--2 km (reducible in processing to 300 m in the along-track direction). At Mars, subsurface returns from SHARAD have been identified in areas known or believed to be predominantly water ice (e.g., the Polar Layered Deposits and mid-latitude lobate debris aprons) as well as those of materials considered to be of volcanic origin (e.g., Medusa Fossae and Amazonis Planitia).
P32B-07
Retrieval of Atmospheric Temperature, Dust, and Water Ice Profiles from one Mars Year of MCS Measurements
Mars Climate Sounder (MCS) is a mid- and far-infrared thermal emission radiometer on board the Mars Reconnaissance Orbiter. It measures radiances in limb and nadir/on-planet geometry from which vertical profiles of atmospheric temperature, water vapor, dust and condensates can be retrieved in an altitude range from 0 to 80 km and with a vertical resolution of ~5 km. MCS has been taking measurements of the Martian surface and atmosphere since Sep. 2006 so the currently available dataset comprises about one Mars year. Here we present results of combined pressure, temperature, dust and water ice profile retrievals from limb measurements during this period. The retrieval is based on a modified Chahine method. Examples of latitudinal cross-sections of these quantities will be shown and seasonal differences will be discussed. Initial results show that dust and temperature in the lower atmosphere are elevated in the northern winter season compared to the southern winter season. Regions of strong middle atmospheric warmings are apparent at both the northern and southern winter pole. Areas of low water ice opacity seem to be associated with these regions, in particular in the northern polar winter.
P32B-08
Color Mosaics and Multispectral Analyses of Mars Reconnaissance Orbit Mars Color Imager (MARCI) Observations
The Mars Color Imager (MARCI) on the Mars Reconnaissance Orbiter (MRO) spacecraft is a is a wide-angle, multispectral Charge-Coupled Device (CCD) "push-frame" imaging camera designed to provide frequent, synoptic-scale imaging of Martian atmospheric and surface features and phenomena. MARCI uses a 1024x1024 pixel interline transfer CCD detector that has seven narrowband interference filters bonded directly to the CCD. Five of the filters are in the visible to short-wave near-IR wavelength range (MARCI-VIS: 437, 546, 604, 653, and 718 nm) and two are in the UV (MARCI-UV: 258 and 320 nm). During the MRO primary mission (November 2006 through November 2008), the instrument has acquired data swaths on the dayside of the planet, at an equator-crossing local solar time of about 3:00 p.m. We are analyzing the MARCI-VIS multispectral imaging data from the MRO primary mission in order to investigate (a) color variations in the surface and their potential relationship to variations in iron mineralogy; and (b) the time variability of surface albedo features at the approx. 1 km/pixel scale typical of MARCI nadir-pointed observations. Raw MARCI images were calibrated to radiance factor (I/F) using pre-flight and in-flight calibration files and a pipeline calibration process developed by the science team. We are using these calibrated MARCI files to generate map-projected mosaics of each of the 30 USGS standard quadrangles on Mars in each of the five MARCI-VIS bands. Our mosaicking software searches the MARCI data set to identify files that match a user- defined set of limits such as latitude, longitude, Ls, incidence angle, emission angle, and year. Each of the files matching the desired criteria is then map-projected and inserted in series into an output mosaic covering the desired lat/lon range. In cases of redundant coverage of the same pixels by different files, the user can set the program to use the pixel with the lowest I/F value for each individual MARCI-VIS band, thus minimizing the "contamination" of the resulting output mosaic by dust or water ice clouds. The user can also optionally specify one of the MARCI-VIS bands to minimize and to use as the template for the other bands. This forces a given location in the mosaic to use the same observation for all five bands. Here we present examples of the MARCI-VIS quadrangle maps generated to date, as well as the results of performing some standard multispectral parameterizations (include the red/blue color ratio, 546 nm band depth, 653 nm band depth, and red to near-IR spectral slope) on the five-band data in order to attempt to detect and map the distribution of iron-bearing minerals that exhibit diagnostic features in the MARCI-VIS wavelength regime. We also show examples of MARCI quadrangles and other regional mosaics from relatively low dust opacity periods in 2006 and 2008 to search for evidence of surface albedo variations associated with the planet-encircling dust event of 2007, and to compare the present albedo patterns to those seen in previous Viking, telescopic, and MGS albedo maps from the 1970s through the 2000s.