Roughness and near‐surface density of Mars from SHARAD radar echoes

Abstract

[1] We present a technique for estimating Mars topographic roughness on horizontal scales from about 10 m to 100 m using Shallow Radar (SHARAD) sounding data. Our results offer a view of surface properties complementary to Mars Orbiter Laser Altimeter (MOLA) pulse-width or baseline roughness maps and can be compared to SHARAD peak-echo properties to infer deviations from the average near-surface density.Latitudinal averaging of SHARAD-derived roughness over Arabia and Noachis Terrae shows good agreement with MOLA-derived roughness and provides clear evidence for latitude-dependent mantling deposits previously inferred from image data. In northwestern Gordii Dorsum, we find that bulk density in at least the upper few meters is significantly lower than in other units of the Medusae Fossae Formation. We observe the same behavior indicative of low near-surface density in wind-eroded crater fill in the southern highlands. Combining surface-properties analysis, subsurface sounding, and high-resolution optical images, we show that the Pavonis Mons fan-shaped deposit differs significantly from lobate debris aprons which SHARAD has shown to be ice-cored. There are no internal radar reflections from the smooth-facies portion of the Pavonis Mons fan-shaped deposit, and we suggest that these deposits are either quite thin or have little dielectric (i.e., density) contrast with the underlying terrain. Future application of these techniques can identify other low-density units across Mars, assist in the mapping of regional volatile-rich mantling units, and provide new constraints on the physical properties of the polar layered terrain.

A New Analysis of Mars “Special Regions”: Findings of the Second MEPAG Special Regions Science Analysis Group (SR-SAG2)

“…Where SHARAD data have resolved the LDAs of Eastern Hellas and Deuteronilus Mensae Plaut et al, 2009a), the hundreds of meters of ice below the debris cover appears relatively debris-free, and the debris cover is interpreted to be of the order of 10-15 m thick. SHARAD has not yet detected buried ice in the residual TMG deposits (Campbell et al, 2013). 5.3.3.…”

Preservation of ancient ice at Pavonis and Arsia Mons: Tropical mountain glacier deposits on Mars

“…Consequently, while the lack of radar detection of ice underlying the smooth facies of the Pavonis Mons smooth facies (Campbell et al, 2013) may indicate that ice is not currently present, the rapid timescales of ice sublimation appear to be at odds with the fresh nature of the RMCs. We note that it is possible (and perhaps more likely) that a tephra-ice mixture with no diagnostic radar reflectors remains present underlying a metersthick tephra/debris cover.…”

“…Is there any evidence of similar remnant ice in the tropical mountain glaciers on Mars? We report here on compelling evidence for the preservation of the order of hundreds of meters of buried ice remaining from the Pavonis and Arsia Mons tropical mountain glaciers, despite the lack of ice detection by the SHARAD orbital radar instrument (Campbell et al, 2013). This ice may preserve records of ancient atmosphere and biology of Mars, and is thus an important exploration target.…”

“…Campbell et al (2013) studied the roughness and near-surface density of the Pavonis Mons deposit using SHARAD data by combining surface-properties analysis, subsurface sounding, and high-resolution optical images. They showed that the Pavonis Mons fan-shaped deposit differs significantly from lobate debris aprons which SHARAD has shown to be ice-cored (Holt et al, 2008;Plaut et al, 2009).…”

Remnant buried ice in the equatorial regions of Mars: Morphological indicators associated with the Arsia Mons tropical mountain glacier deposits

“…For example, it has also been suggested that the Pavonis Mons FSD contains remnant ice in its Smooth Facies deposits (Shean et al, 2005). Recent SHARAD radar profiles, however, did not detect strong reflections in this unit as they did for the LDAs, and as would be expected for an internally layered ice core (Campbell et al, 2013). Head and Weiss (2014) presented geomorphologic evidence for up to several hundred meters of present-day ice under a Z16 m thick debris cover in the Smooth Facies at Pavonis and Arsia Mons.…”