Thermophysical Properties and Surface Heterogeneity of Landing Sites on Mars From Overlapping Thermal Emission Imaging System (THEMIS) Observations

Abstract

Orbitally derived thermal inertia (TI) values of surfaces allow for remote interpretation of rock and sediment physical characteristics. The evolving local times of the Mars Odyssey Thermal Emission Imaging System (THEMIS) mission have enabled surface temperature data collection over multiple seasons and local times over ∼9 Mars years (MY). We utilize this higher temporal resolution data set to separate TI values of individual materials within THEMIS pixels (100 m sampling). In this study, we focus on geologic units within Gusev, Gale, and Jezero crater landing sites to determine their respective TI and ground-truth our methods. We use the KRC model to predict temperatures for a range of homogeneous and two-component thermophysical mixing scenarios (laterally and vertically heterogeneous), and compare those to THEMIS brightness temperatures. The Gusev and Gale crater results are consistent with rover-based evaluations, indurated or clast-covered sands. The best-fit scenarios along the Jezero crater volcanic floor unit show low to moderate TI values representative of coarse sediment, volcaniclastic, or pyroclastic rocks. The light toned unit and western fan deposits both indicate sands and a moderate TI component; we interpret this as heavy fracturing within the rock. Difficulties in modeling some THEMIS temperatures are attributed to daily weather effects, local atmospheric dust variability, and real surface changes over time (e.g., dust deposition and removal); we also observe that some temperature observations lead to non-unique modeled physical solutions. Nevertheless, these methods can still rule out a significant range of material properties and provide meaningful geologic information about Mars' surface.Plain Language Summary Characterizing rock and sediment properties on Mars provides information about its past environmental and surface processes. Thermal inertia (TI) describes how easily materials can be warmed or cooled and can be determined using surface temperatures measured from orbit. TI values are proxies for sediment grain size and rock physical characteristics, which provide clues about Mars' geologic history. The THEMIS instrument, a multispectral thermal infrared camera aboard the Mars Odyssey orbiter, has measured temperatures for 9 Mars years (MY). We have selected three rover landing sites to study with these data. We compare THEMIS temperatures with modeled rock and sediment mixing scenarios. Gusev and Gale crater results agree with rover observations, mixtures of sediment with coarser sediment or lightly cemented rock. A volcanic unit in Jezero crater appears to have formed from volcanic sediments or bubbly lavas. The light toned unit in Jezero is consistent with a brokenup rocky surface covered with sand, and the western fan is dominated by sand-sized sediment. Clouds, dust, and frosts complicate models of THEMIS temperatures. Sometimes, the same temperatures arise from multiple rock/sediment mixing scenarios; this complicates interpretation. However, the methods in this study narrow down ...

CRISM‐Based High Spatial Resolution Thermal Inertia Mapping Along Curiosity's Traverses in Gale Crater

“…Overlapping THEMIS scenes from multiple seasons and years have also been used in a lateral mixing analysis within the Bagnold Dunes (Ahern et al., 2021). In that analysis, the most probable configuration of materials which could produce the observed temperatures is a lateral mixture of fine to medium sands (TI from 182 to 251, effective grain size 100–400 μm) with small amounts of higher‐TI materials (TI from 365 to 600; Ahern et al., 2021).…”

“…Overlapping THEMIS scenes from multiple seasons and years have also been used in a lateral mixing analysis within the Bagnold Dunes (Ahern et al., 2021). In that analysis, the most probable configuration of materials which could produce the observed temperatures is a lateral mixture of fine to medium sands (TI from 182 to 251, effective grain size 100–400 μm) with small amounts of higher‐TI materials (TI from 365 to 600; Ahern et al., 2021). This TI estimate of the sands is consistent with GTS‐derived measurements from the Namib Dune site, and the lateral mixing can be explained by the presence of small amounts of bedrock within the 100 m THEMIS pixels (Ahern et al., 2021).…”

Thermophysical and Compositional Properties of Paleobedforms on Mars

“…The three sites that did satisfy homogeneity criteria (Arcadia Planitia; Lethe Vallis Field 2, Site 1; and Melas Chasma Field 3) had TI of 80 SI, 124 SI, and 190 SI with albedos of 0.24, 0.25, and 0.12, respectively. The lower two sites (TI of 80 SI and 124 SI) could be explained by a thermally thick layer of dust to silt grain sizes, supported by their high albedos (Ahern et al., 2021). The electrostatic properties of dust and silt (Greeley, 1979) would allow such layers to accrue on the steep surfaces of degraded paleobedforms.…”

“…The presence of heterogeneity in geologic materials, such as vertical layering (e.g., dust on top of rock) or lateral mixing (e.g., sand mixed with rocks), causes nonuniform temperature changes on diurnal or seasonal scales, which produces nonunique TI variations (Putzig & Mellon, 2007a). Using single temperature observations to derive TI has been termed “apparent thermal inertia” and cannot fully account for such diurnal or seasonal variability (Ahern et al., 2021; Putzig & Mellon, 2007a). We still derive apparent TI because in situ , rover methods have been used to “ground truth” orbitally derived, apparent TI and illustrate its value in assessing the thermophysical properties of a surface (Edwards et al., 2018).…”

Using near–surface temperature data to vicariously calibrate high-resolution thermal infrared imagery and estimate physical surface properties

“…The effect would potentially be mapped into both the thermal diffusivity estimate (through the effects on the estimated time lag between image pixel response to changing surface radiance and the in situ temperature measured) and the emissivity as the predicted radiance would slightly differ from the observed radiance. The issue of surface heterogeneity and the effects on estimated thermal physical properties is a well-known problem and has been a topic of entire papers (e.g., [ 1 , 3 , 7 ]) Further discussion of the uncertainty in emissivity and diffusivity estimates are discussed below. Emissivity estimates between the best fit using the entire dataset and the best fit using only B Cave ROI increased from 7 to 10%.…”