The inventory of CO2 and H2O and their ability to be transferred between various reservoirs has implications for climate and surface processes. It is therefore important to better characterize these ...reservoirs. Here, we present a THEMIS IR mosaic of the South Polar region of Mars (between -87i?N and -80i?N) acquired during the summer (generally 330 < Ls < 340), when the temperature contrast between the CO2 ice, H2O ice and dust exposed at the surface is the highest. CO2 ice is at ~150 K, whereas H2O ice temperature varies between 185 K and 205 K as a function of local time. Dust is typically 20-40 K hotter than H2O ice. Thus, these three materials can be distinguished by their surface temperature e.g. Titus et al., 2003. Thermal mapping provides consistent results to near IR Bibring et al., 2004 and neutron spectroscopy Feldman et al., 2002, but THEMIS IR images allow a higher spatial sampling (100 m per pixel). Thermal data also provide constraints on the subsurface material's physical nature within a few centimeters as they store and release heat diurnally and seasonally at different rates Titus et al., 2003. Our THEMIS mosaic allows the identification of four thermal units: 1) CO2 ice; 2) H2O ice; 3) dust; 4) intermediate material. The properties of this intermediate unit can be further constrained using seasonal THEMIS and TES data. The diurnal and seasonal temperature variations are not consistent with a single layer structure of the soil but better correspond to a subsurface H2O ice substrate covered by a layer of thin dust whose thickness varies from 0 to a few mm. In 1969, an unusually high concentration of H2O vapor was recorded above the South Pole Barker et al., 1970. Jakosky and Barker 1984 proposed that the perennial cap disappeared, but this hypothesis is not supported by recent work Thomas et al., 2005. Here, we show that the polar region is covered with a thin and widespread layer of dust on a H2O ice substrate. Part of this cover may have been removed in 1969, possibly by the action of strong wind gusts, exposing more ice at the surface and enriching the atmosphere with H2O vapor. Similar events may occur regularly and contribute to the distribution of volatiles on Mars.
Drawing from campus-based research projects sponsored by the AAC&U and the Center for Urban Education at the University of Southern California, "From Equity Talk to Equity Walk" provides practical ...guidance on the design and application of campus change strategies for achieving equitable outcomes. The authors offer advice on how to build an equity-minded campus culture, align strategic priorities and institutional missions to advance equity, understand equity-minded data analysis, develop campus strategies for making excellence inclusive, and move from a first-generation equity educator to an equity-minded practitioner. Central concepts and key points are illustrated through campus examples. The book was also produced by the Center for Urban Education at the University of Southern California.
Observations of recurring slope lineae (RSL) from the High‐Resolution Imaging Science Experiment have been interpreted as present‐day, seasonally variable liquid water flows; however, orbital ...spectroscopy has not confirmed the presence of liquid H2O, only hydrated salts. Thermal Emission Imaging System (THEMIS) temperature data and a numerical heat transfer model definitively constrain the amount of water associated with RSL. Surface temperature differences between RSL‐bearing and dry RSL‐free terrains are consistent with no water associated with RSL and, based on measurement uncertainties, limit the water content of RSL to at most 0.5–3 wt %. In addition, distinct high thermal inertia regolith signatures expected with crust‐forming evaporitic salt deposits from cyclical briny water flows are not observed, indicating low water salinity (if any) and/or low enough volumes to prevent their formation. Alternatively, observed salts may be preexisting in soils at low abundances (i.e., near or below detection limits) and largely immobile. These RSL‐rich surfaces experience ~100 K diurnal temperature oscillations, possible freeze/thaw cycles and/or complete evaporation on time scales that challenge their habitability potential. The unique surface temperature measurements provided by THEMIS are consistent with a dry RSL hypothesis or at least significantly limit the water content of Martian RSL.
Key Points
RSL in Garni crater, Valles Marineris have low water contents (at most ~0.5‐3 wt %)
Thermal data argue against the presence of a circulating briny fluid
RSL experience extreme diurnal temperature cycling, potentially resulting in freeze/thaw/evaporation
The thermal inertia of a planetary surface is a compound function of the regolith thermal conductivity, density and specific heat. On planetary bodies with atmospheres, the conductivity of the ...surface must account for the contributions of both the solid component of the surface as well as that of atmospheric gas found in the interstitial pore spaces. Today, variations in thermal inertia and thermal conductivity on Mars affect the size and timing of areas for which surface temperatures exceed the melting point temperature of water, which is a necessary-but-not-sufficient prerequisite for surface liquid water. Models of past Mars climate, when the atmosphere may have been significantly thicker than at present, have largely neglected the potential role of interstitial atmospheric gas as a thermally conducting element of the ‘surface,’ though we show here that such underestimation of surface conductivity and thermal inertia has no appreciable effect on models of past Mars climate. In more recent Mars history, changes in obliquity have a similar effect of inflating or collapsing the Mars atmosphere, though to a lesser extent. Orbital changes will also modify surface thermal properties, leading to variations in surface conductivity (and thermal inertia) on 105–107 year cycles. We show that these variations, in fact, should not be neglected. We propose an obliquity-driven cycle of surface evolution that drives variability in surface thermal inertia, and suggest that the potential for liquid water at the surface should increase with time following large, positive excursions in Mars' obliquity.
•Atmospheric gas in regolith pore spaces controls surface thermal inertia.•Modern-day Mars is more sensitive to thermal inertia changes than early Mars.•These changes can arise by obliquity-driven induration of surface deposits.•Areas conducive to liquid water grow with time after obliquity excursions.
•Thermal inertia and albedo are derived from ground temperature measurements along the Curiosity rover's traverse.•Diffuse water ice clouds or hazes can significantly influence ground temperatures in ...the southern fall and winter.•The shape of the diurnal ground temperature curve is used to isolate the bedrock thermal inertia from other materials within the sensor footprint.•Thermal inertias of sedimentary rock may be significantly higher than apparent in data sets with sparse local time coverage.
The REMS instrument onboard the Mars Science Laboratory rover, Curiosity, has measured ground temperature nearly continuously at hourly intervals for two Mars years. Coverage of the entire diurnal cycle at 1Hz is available every few martian days. We compare these measurements with predictions of surface-atmosphere thermal models to derive the apparent thermal inertia and thermally derived albedo along the rover's traverse after accounting for the radiative effects of atmospheric water ice during fall and winter, as is necessary to match the measured seasonal trend. The REMS measurements can distinguish between active sand, other loose materials, mudstone, and sandstone based on their thermophysical properties. However, the apparent thermal inertias of bedrock-dominated surfaces (∼350–550Jm−2K−1s−½) are lower than expected. We use rover imagery and the detailed shape of the diurnal ground temperature curve to explore whether lateral or vertical heterogeneity in the surface materials within the sensor footprint might explain the low inertias. We find that the bedrock component of the surface can have a thermal inertia as high as 650–1700Jm−2K−1s−½ for mudstone sites and ∼700Jm−2K−1s−½ for sandstone sites in models runs that include lateral and vertical mixing. Although the results of our forward modeling approach may be non-unique, they demonstrate the potential to extract information about lateral and vertical variations in thermophysical properties from temporally resolved measurements of ground temperature.
Deep convection, as used in meteorology, refers to the rapid ascent of air parcels in the Earth's troposphere driven by the buoyancy generated by phase change in water. Deep convection undergirds ...some of the Earth's most important and violent weather phenomena and is responsible for many aspects of the observed distribution of energy, momentum, and constituents (particularly water) in the Earth's atmosphere. Deep convection driven by buoyancy generated by the radiative heating of atmospheric dust may be similarly important in the atmosphere of Mars but lacks a systematic description. Here we propose a comprehensive framework for this phenomenon of dusty deep convection (DDC) that is supported by energetic calculations and observations of the vertical dust distribution and exemplary dusty deep convective structures within local, regional, and global dust storm activity. In this framework, DDC is distinct from a spectrum of weaker dusty convective activity because DDC originates from pre-existing or concurrently forming mesoscale circulations that generate high surface dust fluxes, oppose large-scale horizontal advective-diffusive processes, and are thus able to maintain higher dust concentrations than typically simulated. DDC takes two distinctive forms. Mesoscale circulations that form near Mars's highest volcanoes in dust storms of all scales can transport dust to the base of the upper atmosphere in as little as two hours. In the second distinctive form, mesoscale circulations at low elevations within regional and global dust storm activity generate freely convecting streamers of dust that are sheared into the middle atmosphere over the diurnal cycle.
•Mars-relevant minerals exhibit a small range of specific heats between 130–320 K.•Composition cannot explain the low thermal inertias of Martian sedimentary outcrops.•The bulk thermal conductivity ...is likely the driver for the low inertia values.
Data returned from Martian missions have revealed a wide diversity of surface mineralogies, including in geological structures interpreted to be sedimentary or altered by liquid water. These terrains are of great interest because of their potential to document the environment at a time when life may have appeared. Intriguingly, Martian sedimentary rocks show distinctly low thermal inertia values (i.e. 300 - 700 Jm−2K−1s−1/2, indicative of a combination of low thermal conductivity, specific heat capacity, and density). These low values are difficult to reconcile with their competent bedrock morphologies, whereas hundreds of bedrock occurrences, interpreted as volcanic in origin, have been mapped globally and display thermal inertia values > 1200 Jm−2K−1s−1/2. Bedrock thermal inertia values are generally assumed to be driven by their bulk thermal conductivity, which in turn is controlled by their micro- and macro-physical properties (i.e., degree and style of cementation in the case of detritic rocks, horizontal fractures and layering, etc.), and not by their density (well-known from terrestrial analog measurements, and with modest variability) or specific heat capacity (generally uncharacterized for non-basaltic materials below room temperature). In this paper, we demonstrate that specific heat capacity cannot be a potential cause for the differential thermophysical behavior between magmatic and sedimentary rocks through a series of experimental Cp(T) measurements at 100–350 K using differential scanning calorimetry. The results on 20 Martian-relevant minerals investigated in this work indicate that these materials exhibit very similar specific heats, ranging from 0.3–0.7 Jg−1K−1 at 100 K to 0.6–1.7 Jg−1K−1 at 350 K. When used in a Martian thermal model, this range of Cp values translate to very small surface temperature differences, indicating that uncertainty in composition (and its effect on the specific heat) is not a noticeable source of thermal inertia variability for indurated units on Mars. We therefore conclude that the low thermal inertia value of sedimentary rocks compared to magmatic/volcanic rocks is likely due to their low apparent bulk conductivity, which bears information on their internal physical structure. Future work combining the analysis of thermal observations acquired at various local times and seasons will help further characterize this heterogeneity.
The S1222a marsquake detected by InSight on 4 May 2022 was the largest of the mission, at MwMa ${M}_{w}^{Ma}$ 4.7. Given its resemblance to two other large seismic events (S1000a and S1094b), which ...were associated with the formation of fresh craters, we undertook a search for a fresh crater associated with S1222a. Such a crater would be expected to be ∼300 m in diameter and have a blast zone on the order of 180 km across. Orbital images were targeted and searched as part of an international, multi‐mission effort. Comprehensive analysis of the area using low‐ and medium‐resolution images reveals no relevant transient atmospheric phenomena and no fresh blast zone. High‐resolution coverage of the epicentral area from most spacecraft are more limited, but no fresh crater or other evidence of a new impact have been identified in those images either. We thus conclude that the S1222a event was highly likely of tectonic origin.
Plain Language Summary
During its time on Mars, NASA's InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission recorded over 1,300 seismic events, known as “marsquakes.” Of these, a number were identified as coming from meteoroid impact cratering events on the surface. The largest event identified by InSight, labeled S1222a, bore some similarities to two large impact events recorded earlier in the mission. In order to investigate whether the S1222a event might also have been caused by an impact event, we undertook a comprehensive search of the region in which the marsquake occurred. We did not identify any fresh craters in the area, implying that the marsquake was likely caused by geological processes.
Key Points
The S1222a marsquake detected by InSight on 4 May 2022 somewhat resembled previous impact‐generated events
We performed an image search in the estimated source region, using data from multiple Mars orbiter missions
No new impact crater has been discovered in this area, pointing to a tectonic origin for the quake
•A clarification for the enumeration of Mars years prior to 1955 is presented.•A short algorithm for computing Ls as a function of the Julian Date is provided.•Fig. 1 indicates robotic presence at ...Mars and selected major global-scale events since Mars year 23.•Table 1 provides a martian calendar for Mars years −183 to 100.
A clarification for the enumeration of Mars years prior to 1955 is presented, along with a table providing the Julian Dates associated with Ls=0° for Mars years −183 (beginning of the telescopic study of Mars) to 100. A practical algorithm for computing Ls as a function of the Julian Date is provided. No new science results are presented.
We derive the depth of the water ice table on Mars by fitting seasonal surface temperature trends acquired by the Mars Climate Sounder and Thermal Emission Imaging System with a two‐layer regolith ...model assuming frozen H2O as the lower material. Our results are consistent with widespread water ice at latitudes as low as 35°N/45°S buried sometimes a few centimeters below sand‐like material, with high lateral ice depth variability, and correlated with periglacial features. While several investigations have already predicted, identified, and characterized some properties of near‐surface ice on Mars, our results constitute a significant advance in the context of the upcoming crewed exploration because (1) they focus on very shallow depths accessible with limited equipment, (2) they provide continuous regional coverage including the midlatitudes, and (3) they yield moderate spatial resolution maps (3 ppd) relevant to landing site selection studies.
Plain Language Summary
Frozen water is a very strong heat conductor compared to typical Martian regolith. As a result, near‐surface ice measurably influences seasonal surface temperature trends, and the depth of the H2O table controls the amplitude of this effect. We leverage this influence on orbital temperature observations using a numerical heat transfer model to derive regional and local maps of the ice depth on Mars, at much higher spatial resolution than previously available. We show that water ice is present sometimes just a few centimeters below the surface, at locations where future landing is realistic, under mobile material that could easily be moved around. This ice could be exploited on‐site for drinking water, breathable oxygen, etc., at a much lower cost than if brought from Earth.
Key Points
Shallow subsurface water ice on Mars influences seasonal surface temperatures in a measurable manner with MCS and THEMIS
We leverage this effect to map the depth to the water ice table at middle and high latitudes
Large continuous units of shallow ice are found ~35°N and ~45°S and could be exploited for future crewed missions
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