Revisiting the thermal inertia of Iapetus: Clues to the thickness of the dark material

Exploring the effects of overburden on the sublimation and transport of H2O on Iapetus

“…These values are supported by radar measurements showing a measurable overburden with a thickness on the order of one to several decimeters and visual evidence of bright ejecta craters indicating the dark material blanket to be no more than a few meters thick Tosi et al, 2010). Thermal modeling has also shown the dark, ice-free, porous overburden to vary in thickness from 7 cm to 16 cm (Rivera-Valentin et al, 2011).…”

“…Due to the recent measurements of the dark terrain's porous, ice-free, overburden thickness and the observed linear trend between it and bolometric Bond albedo (Rivera-Valentin et al, 2011), an estimate of the current stability of water ice within the dark terrain can be produced. Mass transfer through a porous overburden on an airless body at low temperatures has been shown to be in the Knudsen regime (Clifford and Hillel, 1986), where pore wall molecular interactions become a significant means of kinetic energy loss thus greatly inhibiting the sublimation rate compared to the widely used Hertz-Langmuir equation, which has been shown to produce an upper bound estimate of the mass loss rate (Alty and Mackay, 1935;Gundlach et al, 2011;Kossacki et al, 1999).…”

“…Mass transfer through a porous overburden on an airless body at low temperatures has been shown to be in the Knudsen regime (Clifford and Hillel, 1986), where pore wall molecular interactions become a significant means of kinetic energy loss thus greatly inhibiting the sublimation rate compared to the widely used Hertz-Langmuir equation, which has been shown to produce an upper bound estimate of the mass loss rate (Alty and Mackay, 1935;Gundlach et al, 2011;Kossacki et al, 1999). Coupled with the improved global bolometric Bond albedo map and thermal inertia map of Iapetus (Rivera-Valentin et al, 2011), an investigation on the current global stability of water ice can now be more accurately conducted. Global transport of water molecules is addressed in order to estimate the accumulation of water ice and observe if there currently exists sufficient inbound flux at the poles to overcome the darkening effects of exogenic sources.…”

Silicates on Iapetus From Cassini’s Composite Infrared Spectrometer

“…Very fine grains are required to produce this "transparency feature" along with a lack of silicate reststrahlen bands. If silicates are present on Iapetus, then the extremely low thermal inertia values measured there-between 6 and 21 J m −2 K −1 s −1/2 on the leading side (Howett et al 2010;Rivera-Valentin et al 2011), with the uppermost surface <10 J m et al 2005)-are consistent with sub-micron-size grains (Presley & Christensen 1997). However, if the abundance of silicates is low, then they may contribute only negligibly to the total near-surface thermal inertia.…”

Locations of thin liquid water layers on present-day Mars

“…Surface and subsurface temperatures were calculated by solving the one-dimensional thermal diffusion equation using a finite element approach as described by Rivera-Valentin et al (2011), Rivera-Valentin (2012) and Ulrich et al (2010). This method allows for the high spatial resolution required within this study.…”