Assessing the role of clay and salts on the origin of MARSIS basal bright reflections

Mattei, Elisabetta; Pettinelli, Elena; Lauro, Sebastian; Stillman, D. E.; Cosciotti, Barbara; Marinangeli, L.; Tangari, Anna Chiara; Soldovieri, Francesco; Orosei, R.; Caprarelli, Graziella

doi:10.1016/j.epsl.2022.117370

Cited by 23 publications

(45 citation statements)

References 68 publications

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“…While the sample displays σ DC and strong polarization mechanisms, these are not of sufficient magnitude to approach the range of ε a values observed by MARSIS. Thus, our new experiment corroborates the conclusion that salt-H 2 O mixtures in high-surface area sediments do have increased values of σ DC above the eutectic temperature (Mattei et al, 2022;Stillman et al, 2010). While absorbed/bound water does conduct electrical current below and above the eutectic temperature, the ions in adsorbed/bound water are less mobile and follow a much more tortuous path compared to brines in sand or ice (Stillman et al, 2010).…”

Section: Salt-h 2 O Mixtures In High-surface Area Sedimentssupporting

confidence: 84%

“…On one side, perchlorate brines are not expected to be liquid at the values of basal temperatures commonly reported in the literature (e.g., Egea-Gonzáles et al, 2022;Sori & Bramson, 2019). All other types of materials thus far proposed as possible reflectors (Bierson et al, 2021;Grima et al, 2022;Smith et al, 2021), however, have not stood the test of laboratory experiments (Mattei et al, 2022). In the experimental work reported here, we have expanded the types of materials and tested their dielectric properties over a broad range of temperatures, showing that liquid brines and gray hematite are the only materials with a dielectric response consistent with MARSIS observations.…”

Section: Discussionmentioning

confidence: 90%

“…Smith et al (2021) suggested that the dielectric relaxation of clay with adsorbed water at the base of the SPLD could result in high ε a values at the presumed basal temperature in Ultimi Scopuli. However, Smith et al's (2021) data were measured at 230 K and are inconsistent with similar types of measurements as reported in the literature (Cunje et al, 2018;Kułacz & Orzechowski, 2019;Lorek & Wagner, 2013;Mattei et al, 2022;Moore & Maeno, 1993;Stillman & Grimm, 2011a;Stillman et al, 2010). Bierson et al (2021) suggested that jarosite and red hematite are a possible source for the bright reflection.…”

mentioning

confidence: 71%

“…Bierson et al (2021) suggested that the conductivity of saline ice, that is, ice with a bulk salt mass concentration range of 0.1-3.5 wt%, could return ε a values within range of those observed at Ultimi Scopuli. Liquid brines have high ε′ (∼80) and are highly conductive; thus, brines in ice or sediments can plausibly create ε a values within range of those observed by MARSIS (Mattei et al, 2022). Grima et al (2022) suggested that measurements of bulk ε′ > 16 have been reported for ilmenite (FeTiO 3 ) and basalts (Parkhomenko, 1967;Rust et al, 1999;Shmulevich et al, 1971).…”

mentioning

confidence: 93%

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Partially-Saturated Brines Within Basal Ice or Sediments can Explain the Bright Basal Reflections in the South Polar Layered Deposits

Pettinelli

Lauro

et al. 2022

Preprint

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The Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) instrument on Mars Express has detected strong subsurface radar reflections in the region of Ultimi Scopuli (81°S, 193°E), within the South Polar Layered Deposits (SPLD) (Lauro et al., 2021;Orosei et al., 2018). These subsurface reflections are ∼10 dB greater in power than the surrounding reflections and ∼3 dB greater than the reflections from the surface (Orosei et al., 2018). The reflectors are located at the base of the SPLD, approximately 1.5 km below the topographic surface. Because data acquired by MARSIS do not separate the real (ε′) and imaginary (ε″) parts of the complex permittivity of reflectors, the apparent permittivity (ε a ), a single parameter accounting for both ε′ and ε″ (Mattei Abstract Strong radar reflections have been previously mapped at the base of the Martian South Polar Layered Deposits. Here, we analyze laboratory measurements of dry and briny samples to determine the cause of this radar return. We find that liquid vein networks consisting of brines at the grain boundaries of ice crystals can greatly enhance the electrical conductivity, thereby causing strong radar reflections. A brine concentration of 2.7-6.0 vol% in ice is sufficient to match the electrical properties of the basal reflection as observed by Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS). When brine is mixed with sediments, the brine-ice mixture in the pores must be 2-5 times more concentrated in salt, increasing the brine concentration to 6.3-29 vol%. Our best fit of the median observed MARSIS value suggests a salt-bulk sample concentration of ∼6 wt%. Thus, salt enhancement mechanisms on the order of a magnitude greater than the Phoenix landing site are needed. To form brine, the basal reflector must reach a temperature greater than the eutectic temperature of calcium perchlorate of 197.3 ± 0.2 K, which may be possible if more complex thermal modeling is assumed. Colder metastable brines are possible, but stability over millions of years remains unclear. Conversely, gray hematite with a concentration of 33.2-59.0 vol% possess electrical properties that could cause the observed radar returns, but require concentrations 2-3 times larger than anywhere currently detected. We also argue that brines mixed with high-surface-area sediments, or dry red hematite, jarosite, and ilmenite cannot create the observed radar returns at low temperatures.Plain Language Summary Previous research has detected strong radar reflections from the interface between Mars' southern ice cap and their underlying sediments over a region with an area of 20 × 30 km and 1.5 kms beneath the surface. Radar reflections are caused by changes in electrical properties. Here, we analyze electrical property laboratory measurements of materials under Mars-like conditions. We find that a small amount of brine in ice samples could create strong radar reflections similar to those that are observed. A greater concentration of salt is needed in sediment-ice mixtures. We su...

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Section: Salt-h 2 O Mixtures In High-surface Area Sedimentssupporting

confidence: 84%

Section: Discussionmentioning

confidence: 90%

mentioning

confidence: 71%

mentioning

confidence: 93%

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Partially-Saturated Brines Within Basal Ice or Sediments can Explain the Bright Basal Reflections in the South Polar Layered Deposits

Pettinelli

Lauro

et al. 2022

Preprint

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“…MARSIS data processed in the same way as in Orosei et al (2018) can produce bright reflectors over known equatorial volcanic terrains (Grima et al, 2022). Bright basal reflectors can be replicated by physical scenarios that require relatively ice-free material (e.g., Bierson et al, 2021;Lalich et al, 2021) or rely on ubiquitous materials on Mars, such as smectite clays (Smith et al, 2021), though the exact radar properties of smectite clays are still being examined (Mattei et al, 2022). Research to distinguish between clay and brine basal compositions from radar is also underway on the Earth (e.g., Tulaczyk & Foley, 2020).…”

Section: Discussionmentioning

confidence: 99%

Geologic Context of the Bright MARSIS Reflectors in Ultimi Scopuli, South Polar Layered Deposits, Mars

Landis¹,

Whitten²

2022

Geophysical Research Letters

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Radar‐bright basal reflectors have been detected below the South Polar Layered Deposits (SPLD), using Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) data and have an exciting but controversial interpretation: liquid water from subglacial lakes. We mapped the surface of the SPLD immediately above and surrounding the putative lakes (1:2M map scale) in order to provide a geologic context for the interpretation of bright basal reflectors. We use Thermal Emission Imaging System daytime IR (100 m/pixel), Context Camera (6 m/pixel), and High Resolution Imaging Science Experiment (25 cm/pixel) data to characterize geologic units and typical surface roughness. We find evidence for multiple geologic units with features due to CO2 and aeolian‐related processes. We do not find evidence for surface modification linked to postulated lake locations. This is not consistent with the interpretation of the MARSIS basal radar reflector as subglacial lakes.

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Sounding Radars and Ground Penetrating Radars Designed for the Exploration of Our Solar System – Focus on Planet Mars

CIARLETTI

2024

Ground Penetrating Radar

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Assessing the role of clay and salts on the origin of MARSIS basal bright reflections

Cited by 23 publications

References 68 publications

Partially-Saturated Brines Within Basal Ice or Sediments can Explain the Bright Basal Reflections in the South Polar Layered Deposits

Partially-Saturated Brines Within Basal Ice or Sediments can Explain the Bright Basal Reflections in the South Polar Layered Deposits

Geologic Context of the Bright MARSIS Reflectors in Ultimi Scopuli, South Polar Layered Deposits, Mars

Sounding Radars and Ground Penetrating Radars Designed for the Exploration of Our Solar System – Focus on Planet Mars

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