Crater Central Peaks Research Articles

Pristine Noachian crust and key geologic transitions in the lower walls of Valles Marineris: Insights into early igneous processes on Mars

Valles Marineris is a unique vertical section through the uppermost kilometers of the martian crust. Its location, east of the Tharsis bulge, and its water-related history, fuel a great diversity of rock types in this area (Carr, M.H., Head, J.W. [2010]. Earth Planet. Sci. Lett. 294, 185–203). HiRISE and CRISM data available over the walls of the canyon were analyzed to infer the importance of magmatic and sedimentary processes through time. This contribution provides a complete morphologic and mineralogic characterization of the cross-section of rocks exposed in the canyon walls. Low-calcium pyroxene and olivine are detected in the lower portion of the walls, in association with morphologically distinct outcrops, leading to the idea that pristine Noachian crust might be exposed. Phyllosilicates are also present within the walls, but they appear to correspond to an alteration product. No proper sedimentary layers were observed within the walls of Valles Marineris at the resolution available today. All these detections are limited to the eastern portion of Valles Marineris, especially Juventae, Coprates, Capri, and Ganges chasmata. Preserved Noachian crustal material is rare on the martian surface and is rarely exposed in its pristine geologic context. Such detections lend precious information about early igneous processes. This survey also supports observations from the nearby impact crater central peaks (Quantin, C., Flahaut, J., Allemand, P. [2009]. Lunar Planet. Sci. 10; Quantin, C., Flahaut, J., Clenet, H., Allemand, P., Thomas, P. [2011]. Icarus, submitted for publication) and suggests that the western part of Valles Marineris may be cut into another material, consistent with lavas or volcanic sediments.

Regional-scale stratigraphy of surface units in Tyrrhena and Iapygia Terrae, Mars: Insights into highland crustal evolution and alteration history

[1] The compositional, thermophysical and geologic characteristics of surface units in Iapygia and Tyrrhena Terra (60°E–100°E, 0°–30°S) provide new insights into the compositional stratigraphy of the region. Intercrater plains are dominated by two surface units. The older unit (unit 1) is deficient in olivine and more degraded and likely consists of a mixture of impact, volcanic and sedimentary materials. The younger unit (unit 2) is enriched in olivine, exhibits a resistant morphology and higher thermal inertia, and likely represents volcanic infilling of plains. Units 1 and 2 bear a strong resemblance to those previously mapped in Mare Serpentis, a section of highlands crust located northwest of Hellas Basin. Thus, the two major intercrater plains units are even more widespread than previously thought and therefore likely constitute important components of Mars' highland stratigraphy. Many craters in the region contain high thermal inertia deposits (unit 3) that are compositionally identical to unit 2. These may have formed via volcanic infilling or may represent sedimentary materials that have been eroded from crater walls and lithified. Less common units include olivine and/or pyroxene-rich massifs and crater central peaks. These are primarily found within Hellas Basin rim units and may represent mantle materials brought toward the surface during the Hellas impact. Putative chloride deposits are primarily associated with olivine-deficient surfaces (unit 1) that may be heavily degraded occurrences of unit 2. The observations raise a variety of questions related to Martian crustal evolution and alteration that may have more widespread implications outside the study region.

Field reconnaissance geologic mapping of the Columbia Hills, Mars, based on Mars Exploration Rover Spirit and MRO HiRISE observations

Chemical, mineralogic, and lithologic ground truth was acquired for the first time on Mars in terrain units mapped using orbital Mars Reconnaissance Orbiter's High Resolution Imaging Science Experiment (MRO HiRISE) image data. Examination of several dozen outcrops shows that Mars is geologically complex at meter length scales, the record of its geologic history is well exposed, stratigraphic units may be identified and correlated across significant areas on the ground, and outcrops and geologic relationships between materials may be analyzed with techniques commonly employed in terrestrial field geology. Despite their burial during the course of Martian geologic time by widespread epiclastic materials, mobile fines, and fall deposits, the selective exhumation of deep and well-preserved geologic units has exposed undisturbed outcrops, stratigraphic sections, and structural information much as they are preserved and exposed on Earth. A rich geologic record awaits skilled future field investigators on Mars. The correlation of ground observations and orbital images enables construction of a corresponding geologic reconnaissance map. Most of the outcrops visited are interpreted to be pyroclastic, impactite, and epiclastic deposits overlying an unexposed substrate, probably related to a modified Gusev crater central peak. Fluids have altered chemistry and mineralogy of these protoliths in degrees that vary substantially within the same map unit. Examination of the rocks exposed above and below the major unconformity between the plains lavas and the Columbia Hills directly confirms the general conclusion from remote sensing in previous studies over past years that the early history of Mars was a time of more intense deposition and modification of the surface. Although the availability of fluids and the chemical and mineral activity declined from this early period, significant later volcanism and fluid convection enabled additional, if localized, chemical activity.

Central pit craters on Ganymede

Central pit craters are common on Mars, Ganymede and Callisto, and thus are generally believed to require target volatiles in their formation. The purpose of this study is to identify the environmental conditions under which central pit craters form on Ganymede. We have conducted a study of 471 central pit craters with diameters between 5 and 150 km on Ganymede and compared the results to 1604 central pit craters on Mars (diameter range 5–160 km). Both floor and summit pits occur on Mars whereas floor pits dominate on Ganymede. Central peak craters are found in similar locations and diameter ranges as central pit craters on Mars and overlap in location and at diameters <60 km on Ganymede. Central pit craters show no regional variations on either Ganymede or Mars and are not concentrated on specific geologic units. Central pit craters show a range of preservation states, indicating that conditions favoring central pit formation have existed since crater-retaining surfaces have existed on Ganymede and Mars. Central pit craters on Ganymede are generally about three times larger than those on Mars, probably due to gravity scaling although target characteristics and resolution also may play a role. Central pits tend to be larger relative to their parent crater on Ganymede than on Mars, probably because of Ganymede’s purer ice crust. A transition to different characteristics occurs in Ganymede’s icy crust at depths of 4–7 km based on the larger pit-to-crater-diameter relationship for craters in the 70–130-km-diameter range and lack of central peaks in craters larger than 60-km-diameter. We use our results to constrain the proposed formation models for central pits on these two bodies. Our results are most consistent with the melt-drainage model for central pit formation.

Exposure of spectrally distinct material by impact craters on Mercury: Implications for global stratigraphy

MESSENGER’s Mercury Dual Imaging System (MDIS) obtained multispectral images for more than 80% of the surface of Mercury during its first two flybys. Those images have confirmed that the surface of Mercury exhibits subtle color variations, some of which can be attributed to compositional differences. In many areas, impact craters are associated with material that is spectrally distinct from the surrounding surface. These deposits can be located on the crater floor, rim, wall, or central peak or in the ejecta deposit, and represent material that originally resided at depth and was subsequently excavated during the cratering process. The resulting craters make it possible to investigate the stratigraphy of Mercury’s upper crust. Studies of laboratory, terrestrial, and lunar craters provide a means to bound the depth of origin of spectrally distinct ejecta and central peak structures. Excavated red material (RM), with comparatively steep (red) spectral slope, and low-reflectance material (LRM) stand out prominently from the surrounding terrain in enhanced-color images because they are spectral end-members in Mercury’s compositional continuum. Newly imaged examples of RM were found to be spectrally similar to the relatively red, high-reflectance plains (HRP), suggesting that they may represent deposits of HRP-like material that were subsequently covered by a thin layer (∼1 km thick) of intermediate plains. In one area, craters with diameters ranging from 30 km to 130 km have excavated and incorporated RM into their rims, suggesting that the underlying RM layer may be several kilometers thick. LRM deposits are useful as stratigraphic markers, due to their unique spectral properties. Some RM and LRM were excavated by pre-Tolstojan basins, indicating a relatively old age (>4.0 Ga) for the original emplacement of these deposits. Detailed examination of several small areas on Mercury reveals the complex nature of the local stratigraphy, including the possible presence of buried volcanic plains, and supports sequential buildup of most of the upper ∼5 km of crust by volcanic flows with compositions spanning the range of material now visible on the surface, distributed heterogeneously across the planet. This emerging picture strongly suggests that the crust of Mercury is characterized by a much more substantial component of early volcanism than represented by the phase of mare emplacement on Earth’s Moon.

Martian post-impact hydrothermal systems incorporating freezing

We simulate the evolution of post-impact hydrothermal systems within 45 km and 90 km diameter craters on Mars. We focus on the effects of freezing, which alters the permeability structure and fluid flow compared with unfrozen cases. Discharge rates, total discharge and water–rock ratios increase with permeability. Systems with permeabilities of 10 −10 m 2 or higher exhibit convection in the hydrosphere, allowing them to derive heat from greater depths. Surface discharges persist for ∼10 3–10 5 years under freezing surface conditions, with higher permeabilities permitting longer lifetimes. Maximum discharge rates and total discharges range from 0.1 to 10 m 3 s −1 and 10 9 to 10 12 m 3, respectively, for systems with permeabilities between 10 −14 and 10 −12 m 2. Near-surface water–rock ratios range from <1 for low permeability, frozen cases to ∼10 3 for high permeabilities and/or unfrozen cases. Propagation of the freezing front radially inwards focuses flow towards the center of the crater resulting in a diagnostic increase in water–rock ratios there. This process may explain the phyllosilicate assemblages observed at some crater central peaks.

Ultramafic impact melt sheet beneath the South Pole–Aitken basin on the Moon

The Spectral Profiler onboard the Japanese lunar explorer Kaguya conducted the first hyperspectral survey around the South Pole‐Aitken basin (SPA) on the Moon that is one of the largest impact structures in the Solar System. The radiative transfer modeling revealed that fresh crater central peaks inside SPA are commonly composed of an ultramafic assemblage dominated by Magnesium rich orthopyroxene, suggesting a homogeneous layer buried under SPA. The extensive ultramafic layer could be a relic of a gigantic impact melt pool produced by the SPA‐forming impact. The preponderance of orthopyroxene could have resulted from significant fractional crystallization of the lunar magma ocean prior to the onset of plagioclase floatation.

Compositional variations of the lunar crust: Results from radiative transfer modeling of central peak spectra

We present model mineralogy of impact crater central peaks combined with crustal thickness and crater central peak depth of origin models to report multiple perspectives of lunar crustal composition with depth. Here we report the analyses of 55 impact crater central peaks and how their compositions directly relate to the lunar highlands sample suite. A radiative transfer model is used to analyze Clementine visible plus near‐infrared spectra to place compositional constraints on these central peak materials. Central peaks analyzed are dominantly magnesian‐ and plagioclase‐poor; strong compositional similarities to lunar Mg‐suite materials are evident. Relative to crustal thickness estimates, central peak mineralogy becomes more plagioclase‐rich as the crust thickens. Relative to the crust‐mantle boundary, the origin of peaks with dominantly mafic mineralogy are confined to the lower crust and primarily within the South‐Pole Aitken and Procellarum KREEP Terranes (PKT); additionally, central peaks with anorthositic mineralogy (&gt;60 vol % plagioclase) are transported to the surface from all depths in the crustal column and confined to the Feldspathic Highlands Terrane (FHT). The discovery of mafic and magnesian materials, consistent with Mg‐suite rocks of the sample collection, in all lunar terranes suggests that the process and sources that give rise to these types of rocks is not unique to the PKT and not necessarily dependent on incompatible elements for formation. The identification of ferroan and magnesian anorthositic material near the crust‐mantle boundary of the FHT is also inconsistent with an increasing mafic/feldspar ratio and Mg' with depth in the crust.

Discoveries on the lithology of lunar crater central peaks by SELENE Spectral Profiler

The Spectral Profiler (SP) onboard the Japanese SELENE (KAGUYA) spacecraft is now providing global high spectral resolution visible‐near infrared continuous reflectance spectra of the Moon. The reflectance spectra of impact craters on the farside of the Moon reveal lithologies that were not previously identified. The achievements of SP so far include: the most definite detection of crystalline iron‐bearing plagioclase with its characteristic 1.3 μm absorption band on the Moon; a new interpretation of the lithology of Tsiolkovsky crater central peaks, previously classified as “olivine‐rich,” as mixtures of plagioclase and pyroxene; and the lower limit of Mg number of low‐Ca pyroxene found at Antoniadi crater central peak and peak ring which were estimated through direct comparison with laboratory spectra of natural and synthetic pyroxene samples.

The effect of target properties on crater morphology: Comparison of central peak craters on the Moon and Ganymede

Abstract— We examine the morphology of central peak craters on the Moon and Ganymede in order to investigate differences in the near‐surface properties of these bodies. We have extracted topographic profiles across craters on Ganymede using Galileo images, and use these data to compile scaling trends. Comparisons between lunar and Ganymede craters show that crater depth, wall slope and amount of central uplift are all affected by material properties. We observe no major differences between similar‐sized craters in the dark and bright terrain of Ganymede, suggesting that dark terrain does not contain enough silicate material to significantly increase the strength of the surface ice. Below crater diameters of ˜12 km, central peak craters on Ganymede and simple craters on the Moon have similar rim heights, indicating comparable amounts of rim collapse. This suggests that the formation of central peaks at smaller crater diameters on Ganymede than the Moon is dominated by enhanced central floor uplift rather than rim collapse. Crater wall slope trends are similar on the Moon and Ganymede, indicating that there is a similar trend in material weakening with increasing crater size, and possibly that the mechanism of weakening during impact is analogous in icy and rocky targets. We have run a suite of numerical models to simulate the formation of central peak craters on Ganymede and the Moon. Our modeling shows that the same styles of strength model can be applied to ice and rock, and that the strength model parameters do not differ significantly between materials.

Structure, stratigraphy, and origin of Husband Hill, Columbia Hills, Gusev Crater, Mars

The strike and dip of lithologic units imaged in stereo by the Spirit rover in the Columbia Hills using three‐dimensional imaging software shows that measured dips (15–32°) for bedding on the main edifice of the Columbia Hill are steeper than local topography (∼8–10°). Outcrops measured on West Spur are conformable in strike with shallower dips (7–15°) than observed on Husband Hill. Dips are consistent with observed strata draping the Columbia Hills. Initial uplift was likely related either to the formation of the Gusev Crater central peak or ring or through mutual interference of overlapping crater rims. Uplift was followed by subsequent draping by a series of impact and volcaniclastic materials that experienced temporally and spatially variable aqueous infiltration, cementation, and alteration episodically during or after deposition. West Spur likely represents a spatially isolated depositional event. Erosion by a variety of processes, including mass wasting, removed tens of meters of materials and formed the Tennessee Valley primarily after deposition. This was followed by eruption of the Adirondack‐class plains basalt lava flows which embayed the Columbia Hills. Minor erosion, impact, and aeolian processes have subsequently modified the Columbia Hills.

Performance and scientific objectives of the SELENE (KAGUYA) Multiband Imager

Abstract The Multiband Imager (MI) is one of the 14 instruments for the Japanese SELENE (KAGUYA) mission. Goal of the SELENE (KAGUYA) mission is to understand origin and evolution of the Moon by obtaining global element and mineral compositions, topological structure, gravity field of the whole Moon, and electromagnetic and particle environment of the Moon. MI is designed to be a high-resolution multiband imaging camera with a spatial resolution in visible bands of 20 m and a spatial resolution in near-infrared bands of 62 m from the 100 km SELENE (KAGUYA) orbit altitude. The MI flight model has been manufactured and integrated. MTF, viewing vector, over-all sensibility, sensor linearity and electrical noise level (S/N estimation test) were measured, and the results indicate that the MI will provide sufficient MTF and low-noise data, just as estimated in the MI design phase. Operation and data analyses plans have been established, and related tools and algorithms have been developed and checked. One of MI scientific objectives is to investigate small but scientifically very important areas such as crater central peaks and crater walls and to investigate magnesian anorthosites.

The topography of Iapetus' leading side

We have used Cassini stereo images to study the topography of Iapetus' leading side. A terrain model derived at resolutions of 4–8 km reveals that Iapetus has substantial topography with heights in the range of −10 km to +13 km, much more than observed on the other middle-sized satellites of Saturn so far. Most of the topography is older than 4 Ga [Neukum, G., Wagner, R., Denk, T., Porco, C.C., 2005. Lunar Planet. Sci. XXXVI. Abstract 2034] which implies that Iapetus must have had a thick lithosphere early in its history to support this topography. Models of lithospheric deflection by topographic loads provide an estimate of the required elastic thickness in the range of 50–100 km. Iapetus' prominent equatorial ridge [Porco, C.C., and 34 colleagues, 2005. Science 307, 1237–1242] reaches widths of 70 km and heights of up to 13 km from their base within the modeled area. The morphology of the ridge suggests an endogenous origin rather than a formation by collisional accretion of a ring remnant [Ip, W.-H., 2006. Geophys. Res. Lett. 33, doi: 10.1029/2005GL025386. L16203]. The transition from simple to complex central peak craters on Iapetus occurs at diameters of 11 ± 3 km . The central peaks have pronounced conical shapes with flanking slopes of typically 11° and heights that can rise above the surrounding plains. Crater depths seem to be systematically lower on Iapetus than on similarly sized Rhea, which if true, may be related to more pronounced crater-wall slumping (which widens the craters) on Iapetus than on Rhea. There are seven large impact basins with complex morphologies including central peak massifs and terraced walls, the largest one reaches 800 km in diameter and has rim topography of up to 10 km. Generally, no rings are observed with the basins consistent with a thick lithosphere but still thin enough to allow for viscous relaxation of the basin floors, which is inferred from crater depth-to-diameter measurements. In particular, a 400-km basin shows up-domed floor topography which is suggestive of viscous relaxation. A model of complex crater formation with a viscoplastic (Bingham) rheology [Melosh, H.J., 1989. Impact Cratering. Oxford Univ. Press, New York] of the impact-shocked icy material provides an estimate of the effective cohesion/viscosity at 0.04 ± 0.01 MPa/ 0.6 ± 0.2 GPa s . The local distribution of bright and dark material on the surface of Iapetus is largely controlled by topography and consistent with the dark material being a sublimation lag deposit originating from a bright icy substrate mixed with the dark components, but frost deposits are possible as well.

Scientific objectives and specification of the SELENE Multiband Imager

The Lunar Imager/SpectroMeter (LISM) is an instrument being developed for onboarding the SELENE satellite that will be launched in 2007. The LISM consists of the three subsystems: Terrain Camera (TC), Multiband Imager (MI), and Spectral Profiler (SP). The MI is a high-resolution multiband imaging camera consisting of two visible and near infrared sensors. It takes push-broom imaging data by using selected lines of area arrays. The spectral band assignments are 415, 750, 900, 950 and 1000 nm for visible and 1000, 1050, 1250 and 1550 nm for near infrared. The spatial resolution of visible bands is 20 m, and that of near infrared bands is 62 m from the 100 km SELENE orbital altitude. We will observe globally the mineral distribution of the lunar surface in nine band images of MI. Its high spatial resolution will also enable us to investigate small but scientifically very important areas such as crater central peaks and crater walls. The advantage of MI for this aspect is that we can remove topographic effect, which causes false reflectance values seen in the crater wall and crater central peak, by photometric correction with detailed topography. Measurements of MTF, viewing vector, sensor linearity, and stray light and electrical noise level were carried out after the MI integration. Measured data indicate that MI will provide sufficient MTF, low noise and low stray light of spectral imaging data just as estimated in the MI designing phase.

Lander and rover exploration on the lunar surface: A study for SELENE-B mission

The SELENE-B, a lunar landing mission, has been studied in Japan, where a scientific investigation plan is proposed using a robotic rover and a static lander. The main theme to be investigated is to clarify the lunar origin and evolution, especially for early crustal formation process probably from the ancient magma ocean. The highest priority is placed on a direct in situ geology at a crater central peak, “a window to the interior”, where subcrustal materials are exposed and directly accessed without drilling. As a preliminary study was introduced by Sasaki et al. [Sasaki, S., Kubota, T., Okada, T. et al. Scientific exploration of lunar surface using a rover in Japanse future lunar mission. Adv. Space Res. 30, 1921–1926, 2002.], the rover and lander are jointly used, where detailed analyses of the samples collected by the rover are conducted at the lander. Primary scientific instruments are a multi-band stereo imager, a gamma-ray spectrometer, and a sampling tool on the rover, and a multi-spectral telescopic imager, a sampling system, and a sample analysis package with an X-ray spectrometer/diffractometer, a multi-band microscope as well as a sample cleaning and grinding device on the lander.

Verification of the Lunar Crater Central Peak's Rock Types

Verification of the Lunar Crater Central Peak's Rock Types

Scientific exploration of lunar surface using a rover in Japanese future lunar mission

A new lunar mission (SELENE-B) including a lander is now in consideration in Japan. The mission will follow up SELENE (SELenological and ENgineering Explorer, a global remote sensing mission of the moon in 2004). Scientific investigation plans using a rover are proposed: exploration of a crater central peak to discover subsurface materials and exploration of the polar region to discover the trapped ice. We have already developed a 5-wheel engineering-model rover, Micro5, which has a long manipulator with a camera on top. The rover can climb over 15cm steps and rocks by a new suspension system PEGASUS.

Radiative transfer model constraints on the shock state of remotely sensed lunar anorthosites

Near‐IR spectra of some lunar basin rings and crater central peaks exhibit no evidence of absorption due to ferrous iron, unlike all other spectral measurements of lunar soil in the laboratory or obtained remotely. These spectral anomalies have previously been interpreted to indicate the presence of a deposit of essentially pure plagioclase feldspar (anorthosite) which has been shocked above 250 kb. Plagioclase possesses a diagnostic absorption feature near 1250 nm caused by trace ferrous iron that is lost when shocked above 250 kb, whereas ferrous features of pyroxene are robust against shock. However, new methods for computing the optical effects of exposure of lunar materials to the space environment show that these optical effects can obscure the spectral features of plagioclase without resorting to shock modification of the plagioclase structure. Our modeling shows that shock is not necessary to explain the apparent lack of absorption, but is not excluded either. Thus, previous reports that some lunar surface features may have experienced high shock levels are not supported.

Lunar Surface Imaging Polarimetry. III. Langrenus

The program of lunar surface texture analysis conducted with polarimetry at Observatoire de Paris included crater Langrenus. The area was analyzed with the video-polarimeter in terms of albedo, surface roughness, and grain size. An image was produced, mapping the terrain roughness at the surface of the Moon (parameter θ), and another image mapped the median grain size (parameter Md). It is when making these observations that transient bright features were discovered near the crater central peak. They will be analyzed specifically in another paper. The Langrenus floor around the area on which the brightenings occurred is characterized as very rugged terrain at centimeter to meter scale, mantled with a layer made of high-albedo grains of large median size. The ejecta blanket deposited around Langrenus has disymetric textural properties, suggesting that the crater was formed by an oblique impact. A recent impact in the northern part of this aureole excavated the basaltic material beneath the layer and projected onto the surface a dark material which formed a smooth layer.

The topography of Tycho Crater

Three‐dimensional mapping of the Moon can be accomplished with an Earth‐based radar interferometer. Elevation data and radar imagery obtained with this technique are presented for the Tycho Crater area, with a spatial resolution of 200 m and a height resolution of 30 m. The radar maps are displayed in standard cartographic projections with appropriate corrections for elevation‐induced geometric distortions. The digital elevation model allows detailed morphometry of the 85 km diameter crater: the floor of Tycho lies 3970 m below a 1738 km radius sphere, and the crater's central peak rises 2400 m above the floor. The average rim crest elevation is 730 m above the 1738 km datum, giving a mean rim to floor depth of 4700 m. The floor has two distinct units with the western section being higher in elevation by ∼200 m. This dichotomy is consistent with an asymmetry in the crater shape which reveals that maximum wall slumping occurred in the western and southwestern regions of the crater. Comparison of the radar‐derived topography with 87 altimetry points from the Clementine lidar experiment shows rms deviations of ∼90 m after a 0.11° latitude correction to the location of all the Clementine altimetry points.