Supercooled interfacial water in fine-grained soils probed by dielectric spectroscopy

Abstract

Abstract.Water substantially affects nearly all physical, chemical and biological processes on the Earth. Recent Mars observations as well as laboratory investigations suggest that water is a key factor of current physical and chemical processes on the Martian surface, e.g. rheological phenomena. Therefore it is of particular interest to get information about the liquid-like state of water on Martian analogue soils for temperatures below 0 • C. To this end, a parallel plate capacitor has been developed to obtain isothermal dielectric spectra of fine-grained soils in the frequency range from 10 Hz to 1.1 MHz at Martian-like temperatures down to −70 • C. Two Martian analogue soils have been investigated: a Ca-bentonite (specific surface of 237 m 2 g −1 , up to 9.4 % w/w gravimetric water content) and JSC Mars 1, a volcanic ash (specific surface of 146 m 2 g −1 , up to 7.4 % w/w). Three soil-specific relaxation processes are observed in the investigated frequency-temperature range: two weak highfrequency processes (bound or hydrated water as well as ice) and a strong low-frequency process due to counter-ion relaxation and the Maxwell-Wagner effect. To characterize the dielectric relaxation behaviour, a generalized fractional dielectric relaxation model was applied assuming three active relaxation processes with relaxation time of the ith process modelled with an Eyring equation. The real part of effective complex soil permittivity at 350 kHz was used to determine ice and liquid-like water content by means of the Birchak or CRIM equation. There are evidence that bentonite down to −70 • C has a liquid-like water content of 1.17 monolayers and JSC Mars 1 a liquid-like water content of 1.96 monolayers.

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

“…(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).…”

A Pre-Landing Assessment of Regolith Properties at the InSight Landing Site

“…Any liquid or frozen surface water would not be in equilibrium in the equatorial regions of Mars targeted by the InSight lander and would quickly sublimate . However, water within the regolith could still be present in the form of a few monolayers of adsorbed water (Möhlmann 2008), which would maintain liquid-like properties down to temperatures of −70 • C (Lorek and Wagner 2013). This adsorbed water is supposed to reside mainly below depths of a few tens of cm, outside the range of the Martian diurnal and seasonal thermal cycles (Möhlmann 2004).…”

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

“…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.…”