98 research outputs found
Monitoring Atmospheric Dust Spring Activity at High Southern Latitudes on Mars using OMEGA
This article presents a monitoring of the atmospheric dust in the south polar
region during spring of martian year 27. Our goal is to contribute to
identifying the regions where the dust concentration in the atmosphere shows
specific temporal patterns, for instance high, variable, and on the rise due to
lifting or transport mechanisms. This identification is performed in relation
with the seasonal ice regression. Based on a phenomenological examination of
the previous results, hypothesis regarding the origin of aerosol activity of
the southern polar region are proposed. This is of paramount importance since
local dust storms generated in this region sometimes grow to global
proportions.
Characterization and mapping of surface physical properties of Mars from CRISM multi-angular data: application to Gusev Crater and Meridiani Planum
The analysis of the surface texture from the particle (grain size, shape and
internal structure) to its organization (surface roughness) provides
information on the geological processes. CRISM multi-angular observations
(varied emission angles) allow to characterize the surface scattering behavior
which depends on the composition but also the material physical properties
(e.g., grain size, shape, internal structure, the surface roughness). After an
atmospheric correction by the Multi-angle Approach for Retrieval of the Surface
Reflectance from CRISM Observations, the surface reflectances at different
geometries are analyzed by inverting the Hapke photometric model depending on
the single scattering albedo, the 2-term phase function, the macroscopic
roughness and the 2-term opposition effects. Surface photometric maps are
created to observe the spatial variations of surface scattering properties as a
function of geological units at the CRISM spatial resolution (200m/pixel). An
application at the Mars Exploration Rover (MER) landing sites located at Gusev
Crater and Meridiani Planum where orbital and in situ observations are
available, is presented. Complementary orbital observations (e.g. CRISM
spectra, THermal EMission Imaging System, High Resolution Imaging Science
Experiment images) are used for interpreting the estimated Hapke photometric
parameters in terms of physical properties. The in situ observations are used
as ground truth to validate the interpretations. Varied scattering properties
are observed inside a CRISM observation (5x10km) suggesting that the surfaces
are controlled by local geological processes (e.g. volcanic resurfacing,
aeolian and impact processes) rather than regional or global. Consistent
results with the in situ observations are observed thus validating the approach
and the use of photometry for the characterization of Martian surface physical
properties
Surface reflectance of Mars observed by CRISM/MRO: 2. Estimation of surface photometric properties in Gusev Crater and Meridiani Planum
The present article proposes an approach to analyze the photometric
properties of the surface materials from multi-angle observations acquired by
the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on-board the
Mars Reconnaissance Orbiter. We estimate photometric parameters using Hapke
model in a Bayesian inversion framework. This work also represents a validation
of the atmospheric correction provided by the Multi-angle Approach for
Retrieval of Surface Reflectance from CRISM Observations (MARS-ReCO) proposed
in the companion article.The latter algorithm retrieves photometric curves of
surface materials in reflectance units after removing the aerosol contribution.
This validation is done by comparing the estimated photometric parameters to
those obtained from in situ measurements by Panoramic Camera instrument at the
Mars Exploration Rover (MER)-Spirit and MER-Opportunity landing sites.
Consistent photometric parameters with those from in situ measurements are
found, demonstrating that MARS-ReCO gives access to accurate surface
reflectance. Moreover the assumption of a non-Lambertian surface as included in
MARS-ReCO is shown to be significantly more precise to estimate surface
photometric properties from space in comparison to methods based on a
Lambertian surface assumption. In the future, the presented method will allow
us to map from orbit the surface bidirectional reflectance and the related
photometric parameters in order to characterize the Martian surface
Pluto's lower atmosphere structure and methane abundance from high-resolution spectroscopy and stellar occultations
Context: Pluto possesses a thin atmosphere, primarily composed of nitrogen,
in which the detection of methane has been reported.
Aims: The goal is to constrain essential but so far unknown parameters of
Pluto's atmosphere such as the surface pressure, lower atmosphere thermal
stucture, and methane mixing ratio.
Methods: We use high-resolution spectroscopic observations of gaseous
methane, and a novel analysis of occultation light-curves.
Results: We show that (i) Pluto's surface pressure is currently in the 6.5-24
microbar range (ii) the methane mixing ratio is 0.5+/-0.1 %, adequate to
explain Pluto's inverted thermal structure and ~100 K upper atmosphere
temperature (iii) a troposphere is not required by our data, but if present, it
has a depth of at most 17 km, i.e. less than one pressure scale height; in this
case methane is supersaturated in most of it. The atmospheric and bulk surface
abundance of methane are strikingly similar, a possible consequence of the
presence of a CH4-rich top surface layer.Comment: AA vers. 6.1, LaTeX class for Astronomy & Astrophysics, 9 pages with
5 figures Astronomy and Astrophysics Letters, in pres
Hydrothermal Alteration of Ultramafic Rocks in Ladon Basin, Mars - Insights From CaSSIS, HiRISE, CRISM, and CTX
The evolution of the Ladon basin has been marked by intense geological activity and the discharge of huge volumes of water from the Martian highlands to the lowlands in the late Noachian and Hesperian. We explore the potential of the ExoMars Trace Gas Orbiter/Color and Stereo Surface Imaging System color image data set for geological interpretation and show that it is particularly effective for geologic mapping in combination with other data sets such as HiRISE, Context, and Compact Reconnaissance Imaging Spectrometer for Mars. The study area displays dark lobate flows of upper Hesperian to early Amazonian age, which were likely extruded from a regional extensional fault network. Spectral analysis suggests that these flows and the underlying rocks are ultramafic. Two distinct altered levels are observed below the lobate flows. The upper, yellow-orange level shows hundreds of structurally controlled narrow ridges reminiscent of ridges of listwanite, a suite of silicified, fracture-controlled silica-carbonate rocks derived from an ultramafic source and from serpentine. In addition to serpentinite, the detected mineral assemblages may include chlorite, carbonates, and talc. Kaolin minerals are detected in the lower, white level, which could have formed by groundwater alteration of plagioclase in the volcanic pile. Volcanism, tectonics, hydrothermal activity, and kaolinization are interpreted to be coeval, with hydrothermal activity and kaolinization controlled by the interactions between the aquifer and the hot, ultramafic lobate flows. Following our interpretations, East Ladon may host the first listwanite ridges described on Mars, involving a hydrothermal system rooted in a Hesperian aquifer and affecting ultramafic rocks from a magmatic source yet to be identified
Small Scale Topographical Characterization of Oxia Planum, Mars
International audienceOxia Planum, in the Arabia Terra region of Mars, will be the site of ExoMars Rosalind Franklin Rover exploration in 2021. Oxia Planum, contains Noachian (i.e. ancient, > 3.7 Ga) terrains that become increasingly eroded towards the crustal dichotomy which separates the ancient southern highlands from the younger southern lowlands. The site has a rich geological history showing diverse aqueous episodes during the Noachian, followed by later volcanic and aeolian/erosional activity. Oxia Planum contains abundant phyllosilicate materials. We perform the topographical characterization of parts of Oxia Planum at metric to hectometric horizontal scales by generating improved high-resolution digital elevation models (DEMs). In this work we focus on slope at different scales that are useful to constrain past and present geological processes and to prepare the future traverse of the rover
Icy lanes on Titan
International audienc
Small Scale Topographical Characterization of Jezero Crater Region, Mars.
International audienceWe perform the topographical characterization of the Jezero region of Mars down to the metric horizontal scale by generating improved high-resolution DEMs
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