Description: Publication date: Available online 28 December 2013 Source: Planetary and Space Science Author(s): F. Franchi , A.P. Rossi , M. Pondrelli , B. Cavalazzi Conical mounds and furrows are widely interpreted as the morphological evidences of fluids expulsion on the martian surface. In the Crommelin crater (equatorial Arabia Terra) furrows and conical mounds are exhumed within light-toned equatorial layered deposits (ELDs). Aim of this paper is to describe these landforms and discuss their potential relations with water upwelling in Crommelin area. A comparative study of some of the morphologies hosted in the Crommelin area deposits have been performed by using multiple datasets (CTX, HRSC, MOLA, HiRISE). Then examples of spring and conical mounds on Earth was examined for comparison with analogue structures on Mars. In this work thickness and geometries of the crater filling sediment packages have been calculated. Stratigraphic contacts and relations have been also reported in Crommelin area revised geological map, and mound clusters, potentially fluid-related morphologies, from Crommelin, Firsoff and Southern crater have been detailed. The morphometric and morphological analyses revealed that mounds and other structures occur where the ELDs are thicker and crudely layered. In addition, orthorectified imagery and high-resolution topography indicated the presence of conical mounds within the upper portion of ELDs near the craters rims. Mounds show apical holes and are linked to elongated structures resembling veins and dikes. Elongated structures (furrows) and concentric strata pattern that we refer to as ridge-and-through, were described inside to Crommelin crater. MOLA-based DEMs revealed that these morphologies developed within a flat topography and are inconsistent with gravitative processes. The results suggest that the inferred sediments package was likely part of an extensive zone of groundwater upwelling. This long-wavelength flow controlled water and sediments supply into the study area, probably during a major climate shift. Fluid expulsion processes were recognized as a relevant process in the formation of these morphologies. Mounds, furrows and related structures could be linked with deep fracture systems generated during the impact that trigger the potential upwelling of groundwater, at some point after the impact itself. As a consequence, groundwater upwelling could be expected in other craters on Mars with Crommelin-like topographic and geological setting.

Description: Publication date: Available online 28 December 2013 Source: Planetary and Space Science Author(s): James L. Fastook , James W. Head Concentric Crater Fill (CCF) occurs in the interior of impact craters in mid- to high latitudes on Mars and is interpreted to have formed by glacial ice flow and debris covering. We use the characteristics and orientation of deposits comprising CCF, the thickness of pedestal deposits in mid- to high-latitude pedestal craters (Pd), the volumes of the current polar caps, and information about regional slopes and ice rheology to address questions about 1) the maximum thickness of regional ice deposits during the Late Amazonian, 2) the likelihood that these deposits flowed regionally, 3) the geological regions and features most likely to induce ice-flow, and 4) the locations and environments in which ice is likely to have been sequestered up to the present. We find that regional ice flow under Late Amazonian climate conditions requires ice thicknesses exceeding many hundreds of meters for slopes typical of the vast majority of the surface of Mars, a thickness for the mid-latitudes that is well in excess of the total volume available from polar ice reservoirs. This indicates that although conditions for mid- to high-latitude glaciation may have persisted for tens to hundreds of millions of years, the process is “supply limited”, with a steady state reached when the polar ice cap water ice supply becomes exhausted. Impact craters are by far the most abundant landform with associated slopes (interior wall and exterior rim) sufficiently high to induce glacial ice flow under Late Amazonian climate conditions, and topographic slope data show that Amazonian impact craters have been clearly modified, undergoing crater interior slope reduction and floor shallowing. We show that these trends are the predictable response of ice deposition and preferential accumulation and retention in mid- to high-latitude crater interiors during episodes of enhanced spin-axis obliquity. We demonstrate that flow from a single episode of an inter-crater terrain layer comparable to Pedestal Crater deposit thicknesses (∼50 m) cannot fill the craters in a time period compatible with the interpreted formation times of the Pedestal Crater mantled ice layers. We use a representative obliquity solution to drive an ice flow model and show that a cyclical pattern of multiply recurring layers can both fill the craters with a significant volume of ice, as well as transport debris from the crater walls out into the central regions of the craters. The cyclical pattern of waxing and waning mantling layers results in a rippled pattern of surface debris extending out into the crater interiors that would manifest itself as an observable concentric pattern, comparable in appearance to concentric crater fill. In this scenario, the formation of mantling sublimation till layers seals the accumulating ice and sequesters it from significant temperature variations at diurnal, annual and spin-axis/orbital cycle time scales, to produce ancient ice records preserved today below CCF crater floors. Lack of meltwater features associated with concentric crater fill provides evidence that the Late Amazonian climate did not exceed the melting temperature in the mid- to high-latitudes for any significant period of time. Continued sequestration of ice with time in CCF and related deposits (lobate debris aprons and lineated valley fill) further reduces the already supply-limited polar ice sources, suggesting that there has been a declining reservoir of available ice with each ensuing glacial period. Together, these deposits represent a candidate library of climate chemistry and global change dating from the Late Amazonian, and a non-polar water resource for future exploration. Graphical abstract

Description: Publication date: Available online 26 December 2013 Source: Planetary and Space Science Author(s): Thomas C. Duxbury , Alexander V. Zakharov , Harald Hoffmann , Edward A. Guinness We review the previous exploration of Phobos and Deimos by spacecraft. The first close-up images of Phobos and Deimos were obtained by the Mariner 9 spacecraft in 1971, followed by much image data from the two Viking orbiters at the end of the seventies, which formed the basis for early Phobos and Deimos shape and dynamic models. The Soviet Phobos 2 spacecraft came within 100 km of landing on Phobos in 1988. Mars Global Surveyor (1996–2006) and Mars Reconnaissance Orbiter (since 2005) made close-up observations of Phobos on several occasions. Mars Express (since 2003) in its highly elliptical orbit is currently the only spacecraft to make regular Phobos encounters and has returned large volumes of science data for this satellite. Landers and rovers on the ground (Viking Landers, Mars Pathfinder, MER rovers, MSL rover) frequently made observations of Phobos, Deimos and their transits across the Solar disk.

Description: Publication date: Available online 21 December 2013 Source: Planetary and Space Science Author(s): C. Tornow , P. Gast , U. Motschmann , S. Kupper , E. Kührt , I. Pelivan The formation of water is a repetitive process and depends on the physical conditions in the different stages of the solar nebula and early solar system. Our solar nebula model considers the thermal and chemical evolution of a collapsing globular cloud core. We simulate the collapse with a semi-analytical model which is based on a multi-zone density distribution. This model describes the formation of a central protostellar object surrounded by a disk and a thin outer envelope. It considers an adiabatic equation of state, viscous gas flow and a resistive magnetic field. Due to the low temperatures in the hydrostatic stage of the core, icy layers of water mixed with other molecules build on the dust grains. In the course of the collapse the ice sublimates and drives a complex chemical evolution located in a warm region around the proto-stellar object called hot corino. Moreover, the relatively high temperatures in this region allow the gas phase formation of water together with other molecules. The abundances of the chemical compounds are computed from rate equations solved in a Lagrangian grid. We can show that there was high water density in the early and late accretion zone of the Earth. This water was sublimated from the dust or formed by hot neutral reactions in the gas phase. Thus, according to our collapse model, there were two sources delivering the water incorporated into the Earth.

Description: Publication date: Available online 19 December 2013 Source: Planetary and Space Science Author(s): Oleg S. Ugolnikov , Igor A. Maslov The paper describes the study of scattered radiation field in the mesosphere basing on wide-angle polarization camera (WAPC) measurements of the twilight sky background and single scattering separation procedure. Mid-August observations in 2012 and 2013 show the decrease of single scattering polarization value probably related with Perseids meteor dust moderation in the upper mesosphere. Effect correlates with activity of tiny fraction of Perseids shower. Polarization and temperature analysis allows estimating the altitude of dust layer and character polarization of dust scattering.

Description: Publication date: Available online 18 December 2013 Source: Planetary and Space Science Author(s): F. Schmidt , I. Shatalina , M. Kowalski , N. Gac , B. Saggin , M. Giuranna The Planetary Fourier Spectrometer (PFS) onboard Mars Express (MEx) is the instrument with the highest spectral resolution observing Mars from orbit since January 2004. It permits studying the atmospheric structure, major and minor compounds. The present time version of the calibration is limited by the effects of mechanical vibration, currently not corrected. We proposed here a new approach to correct for the vibrations based on semi-blind deconvolution of the measurements. This new approach shows that a correction can be done efficiently with 85% reduction of the artifacts, in a equivalent manner to the stacking of 10 spectra. Our strategy is not fully automatic due to the dependence on some regularisation parameters. It may be applied on the complete PFS dataset, correcting the large-scale perturbation due to microvibrations for each spectrum independently. This approach is validated on actual PFS data of Short Wavelength Channel (SWC), perturbed by microvibrations. A coherence check can be performed and also validate our approach. Unfortunately, the coherence check can be done only on the first 310 orbits of MEx only, until the laser line has been switch off. More generally, this work may apply to numerically “deshake” Fourier Transform Spectrometer (FTS), widely used in space experiments or in the laboratory. Graphical abstract Highlights From blue to green: raw PFS spectra to corrected spectra. Fake structures are located with arrows. Our method is able to correct single PFS spectra but also to remove fake structure.

Description: Publication date: Available online 18 December 2013 Source: Planetary and Space Science Author(s): M.J.A. Bolzan , E. Echer We studied the magnetic field turbulence in Jupiter's magnetosheath during the Ulysses inbound trajectory in 1992. This analysis was conducted using nonlinear techniques such as kurtosis, probability density functions, multifractal approach and wavelet analysis. The results from the PDFs and kurtosis analysis, for each magnetic field component, show a strongly non-Gaussian behavior on shorter periods. The multifractal analysis suggests that the fluctuations can be described with a multifractal law due to the intermittent turbulence in the scales from 2 to 200 seconds. The large magnetic field compressional pulse observed by Tsurutani et al. (1993a) may be the main cause that introduces the intermittency and multifractal behavior for the signal, causing the reduction of the power law=−2.

Description: Publication date: Available online 17 December 2013 Source: Planetary and Space Science Author(s): B. Klinger , O. Baur , T. Mayer-Gürr The NASA mission GRAIL (Gravity Recovery And Interior Laboratory) makes use of low-low satellite-to-satellite tracking between the spacecraft GRAIL-A (Ebb) and GRAIL-B (Flow) to determine high-resolution lunar gravity field features. The inter-satellite measurements are independent of the visibility of the spacecraft from Earth, and hence provide data for both the nearside and the farside of the Moon. We propose to exploit this ranging data by an integral equation approach using short orbital arcs; it is based on the reformulation of Newton's equation of motion as a boundary value problem. This technique has been successfully applied for the recovery of the gravity field of the Earth from the Gravity Recovery And Climate Experiment (GRACE) project—the terrestrial sibling of GRAIL. By means of a series of simulation studies we demonstrate the potential of the approach. We pay particular attention on a priori gravity field information, orbital arc length, observation noise and the impact of spectral aliasing (omission error). Finally, we compute a first lunar gravity model (GrazLGM200a) from real data of the primary mission phase (March 1, 2012 to May 29, 2012). The unconstrained model is expanded up to spherical harmonic degree and order 200. From our simulations and real data results we conclude that the integral equation approach is well suited for GRAIL gravity field recovery.

Description: Publication date: Available online 17 December 2013 Source: Planetary and Space Science Author(s): K. Willner , X. Shi , J. Oberst The global shape and the dynamic environment are fundamental properties of a body. Other properties such as volume, bulk density, and models for the dynamic environment can subsequently be computed based on such models. Stereo-photogrammetric methods were applied to derive a global digital terrain model (DTM) with 100 m/pixel resolution using High Resolution Stereo Camera images of the Mars Express mission and Viking Orbiter images. In a subsequent least-squares fit, coefficients of the spherical harmonic function to degree and order 45 are computed. The dynamic models for Phobos were derived from a polyhedron representation of the DTM. The DTM, spherical harmonic function model, and dynamic models, have been refined and represent Phobos' dynamic and geometric topography with much more detail when compared to Shi et al. (2012) and Willner et al. (2010) models, respectively. The volume of Phobos has been re-determined to be in the order of 5741 km 3 with an uncertainty of only 0.6% of the total volume. This reduces the bulk density to 1.86±0.013 g/cm 3 in comparison to previous results. Assuming a homogeneous mass distribution a forced libration amplitude for Phobos of 1.14° is computed that is in better agreement with observations by Willner et al. (2010) than previous estimates.

Description: Publication date: Available online 17 December 2013 Source: Planetary and Space Science Author(s): Seth J. Kadish , James W. Head , James L. Fastook , David R. Marchant Fan-shaped deposits (FSDs) extending to the northwest of the Tharsis Montes on Mars are the remnants of Amazonian-aged, cold-based, tropical mountain glaciers. We use high-resolution images to perform new impact crater size-frequency distribution (CSFD) analyses on these deposits in an effort to constrain the timing and duration of ice accumulation at tropical latitudes on Mars. This analysis revises the current understanding of the chronology regarding the formation of the glaciers and of the ridged facies in the Arsia Mons deposit, a deposit interpreted to be formed from recessional cold-based drop moraines. We develop a conceptual model that illustrates the effect of moving glacial ice on superposed impact craters of various sizes, including the buffering of underlying geologic units from impacts caused by the presence of the ice for extended periods of time, and the interpretation of crater retention ages of the subsequent glacial deposits following the periods of active glaciation. The new CSFD analyses establish best-fit crater retention ages for each entire Tharsis Montes FSD; these are ~220 Ma for the Ascraeus FSD at 8.35°S, ~125 Ma for the Pavonis FSD at 1.48°N, and ~210 Ma for the Arsia FSD at 11.92°N. Because the age for each deposit represents a combination of the stratigraphically older ridged facies and the younger knobby and smooth facies, the crater retention ages are most likely to represent dates subsequent to the onset of glaciation and prior to its final cessation. Estimates of the time necessary to build the deposits using net accumulation rates from atmospheric general circulation models and emplacement rates from glacial flow models suggest durations of ~45–150 Ma, depending on the specific obliquity history. These surface crater retention ages and related age estimates require that massive volumes of ice (on the order of 10 5 km 3 ) were emplaced at tropical latitudes on Mars during the Middle to Late Amazonian. Additionally, we determined CSFD ages of three adjacent drop moraine units at Arsia Mons (725 Ma, 475 Ma and 345 Ma) and used these to calculate the average amount of time needed to form one of the approximately 185 drop moraines forming these deposits; we found that a typical drop moraine formation time in the Arsia FSD ridged facies to be on the order of ~10 6 years. These formation ages are considerably longer than that required for typical moraine systems alongside dynamic, wet-based glaciers on Earth, but are in approximate accord with recent geomorphological and geochemical data that document long-term, ice-margin stability for several cold-based glaciers in interior Antarctica. The difference in the ages of the ridged facies and non-ridged portion of the Arsia FSD suggests that the tropical mountain glaciers may have been emplaced over a period spanning many hundreds of millions of years. CSFD measurements for lava flows predating and postdating the Arsia Mons FSD suggest a maximum possible age of 〈750 Ma and a minimum age for the late stage, post FSD lava flows of ~105 Ma. Taken together, this evidence supports a scenario in which ice has been present and stable in substantial quantities (~10 5 –10 6 km 3 ) at tropical latitudes during extended periods of the Middle to Late Amazonian history of Mars. This implies that during this time, Mars sustained periods of spin-axis obliquity in the vicinity of 45°, during which time polar ice deposits were substantially reduced in volume or perhaps even absent.