New Insights Into Subsurface Stratigraphy Northwest of Ascraeus Mons, Mars, Using the SHARAD and MARSIS Radar Sounders

The Tharsis Montes volcanoes on Mars are the source of laterally extensive lava flows and other volcanic deposits generating a complex stratigraphy throughout the Tharsis Volcanic Province. We use SHAllow RADar (SHARAD) and Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) observations in a region northwest of Ascraeus Mons to determine the composition, density, thickness, and spatial distribution of these emplaced volcanic materials. We identified subsurface reflectors along 43 SHARAD and five MARSIS observations. Reflectors in the volcanic plains are interpreted to be sequences of basaltic lava flows with interspersed pyroclastic material, dust, or regolith during a hiatus in activity. Others correspond to the base of three major flow fields. Several plain reflectors were detected by both MARSIS and SHARAD. Other notable reflectors were identified near Ascraeus' flank where lava buried glacially derived sediment. We derived thickness and other material properties for flows using their distinct topographic boundary visible in the radar images. Permittivity ranged from 7.0 to 11.2 corresponding to lava flow densities of 3.20–3.52 g/cm3. Flow thicknesses ranged from 19.8 to 60.2 m. Loss tangents were low for the flow fields ranging from 0.024 to 0.043. Loss tangents in the plains ranged from 0.010 to 0.076. Higher loss tangents correspond to lossier regions that may have higher concentrations of radar absorbing minerals like hematite. Surface roughness controls where reflectors are detected. SHARAD detects the base of three out of the four flow fields in this region with muted surface roughness from dust mantling and erosion. © 2022. American Geophysical Union. All Rights Reserved.6 month embargo; first published: 31 May 2022This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

MARSIS surface reflectivity of the south residual cap of Mars

International audienceThe south residual cap of Mars is commonly described as a thin and bright layer of CO-ice. The Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) is a low-frequency radar on board Mars Express operating at the wavelength between 55 and 230 m in vacuum. The reflection of the radar wave on a stratified medium like the residual cap can generate interferences, causing weaker surface reflections compared to reflections from a pure water ice surface

Inter-annual variability of Mars Polar processes as observed by OMEGA/Mars Express

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The 3-5 MHz global reflectivity map of Mars by MARSIS/Mars Express: Implications for the current inventory of subsurface H2O

International audienceWe extracted the surface echo power from two years of MARSIS measurements. The retrieved values are calibrated to compensate for changes in the distance of the spacecraft to the surface and for the attenuation of the signal by the ionosphere. The results are used to build the first global map of surface echo power at 3-5 MHz. The surface echo power variations are primarily caused by km-scale surface roughness. Then, we derive the values of dielectric constant of the shallow subsurface materials by normalizing the surface echo power map using a simulation of MARSIS signal from the MOLA topography. As a result, we obtain a map that characterizes the dielectric properties of the materials down to a few decameters below the surface. Dielectric properties vary with latitude, with high values in mid-latitudes belts (20-40°) and lower values at both equatorial and high latitudes. From the comparison of MARSIS reflectivity map to GRS observations, we conclude that the reflectivity decrease observed poleward of 50-60° corresponds to the onset of water-ice occurrence within the regolith. Assuming homogenous ground composition and texture at the scale of the MARSIS resolution cell, our inferred volume of ground water ice is of 10 km, equivalent to a polar cap. Low reflectivity areas are also observed in equatorial regions. From radar studies alone, equatorial low dielectric constant values could have different interpretations but the correlation with GRS hydrogen distribution rather points toward a water related explanation

Radar subsurface sounding over the putative frozen sea in Cerberus Palus, Mars

The area of Mars known as Cerberus Palus, suspected of harboring a frozen body of water, has been observed by the two subsurface sounding radar MARSIS and SHARAD. SHARAD data reveal subsurface interfaces at depths ranging from ~50 m to ~150 m which could be interpreted as either the bottom of an ice sheet lying over bedrock, or an interface between two lava flows. Echoes have been analyzed to estimate the dielectric properties of the surface layer, and results favor the interpretation that no ice is present in the area

Energetic particle showers over Mars from comet Siding-Spring

International audienceOn October 19th 2014, Mars experienced a close encounter with Comet C/2013 A1 (Siding Spring), at a distance of only 141,000 km, or one third the Earth Moon distance. The gaseous coma washed over Mars and Mars passed directly through the cometary debris stream [1]. As a close encounter of this type is predicted only once in 100,000 years, this is likely the only opportunity for measurements associated with planetary/cometary encounters. Additionally, the encounter was masked by the transit of a powerful Coronal Mass Ejection (CME) 44 hours before [2]. Thus, the comet flyby took place when the Martian plasma system was still recovering from the CME impact, whilst the solar wind passing Mars remained significantly disturbed. In this study, we investigate the interaction of the comet with the solar wind, and their effects on the shock-accelerated energetic particles that precipitate into the Mars’ atmosphere. The study is based on data from MAVEN, Mars Odyssey, MSL and Mars Express missions