Water on Mars, With a Grain of Salt: Local Heat Anomalies Are Required for Basal Melting of Ice at the South Pole Today

Recent analysis of radar data from the Mars Express spacecraft has interpreted bright subsurface radar reflections as indicators of local liquid water at the base of the south polar layered deposits (SPLD). However, the physical and geological conditions required to produce melting at this location were not quantified. Here we use thermophysical models to constrain parameters necessary to generate liquid water beneath the SPLD. We show that no concentration of salt is sufficient to melt ice at the base of the SPLD in the present day under typical Martian conditions. Instead, a local enhancement in the geothermal heat flux of >72 mW/m(2) is required, even under the most favorable compositional considerations. This heat flow is most simply achieved via the presence of a subsurface magma chamber emplaced 100 s of kyr ago. Thus, if the liquid water interpretation of the observations is correct, magmatism on Mars may have been active extremely recently.6 month embargo; published online: 12 February 2019This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Cryovolcanic rates on Ceres revealed by topography

Cryovolcanism, defined here as the extrusion of icy material from depth, may be an important planetary phenomenon in shaping the surfaces of many worlds in the outer Solar System and revealing their thermal histories. However, the physics, chemistry and ubiquity of this geologic process remain poorly understood, especially in comparison to the better-studied silicate volcanism on the terrestrial planets. Ceres is the only plausibly cryovolcanic world to be orbited by a spacecraft up to now, making it the best opportunity to test the importance of cryovolcanism on bodies in the outer Solar System and compare its effects to silicate volcanism on terrestrial planets. Here, we analyse images from NASA’s Dawn mission and use the finite element method to show that Ceres has experienced cryovolcanism throughout its geologic history, with an average cryomagma extrusion rate of ~10^4 m^3 yr^(−1). This result shows that volcanic phenomena are important on Ceres, but orders of magnitude less so than on the terrestrial planets

Mars as a "natural laboratory" for studying surface activity on a range of planetary bodies

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Effect of cytomegalovirus infection on breastfeeding transmission of HIV and on the health of infants born to HIV-infected mothers

Cytomegalovirus (CMV) infection can be acquired in utero or postnatally through horizontal transmission and breastfeeding. The effect of postnatal CMV infection on postnatal HIV transmission is unknown

Plasma Micronutrient Concentrations Are Altered by Antiretroviral Therapy and Lipid-Based Nutrient Supplements in Lactating HIV-Infected Malawian Women

Background: Little is known about the influence of antiretroviral therapy with or without micronutrient supplementation on the micronutrient concentrations of HIV-infected lactating women in resource-constrained settings

Radar Analysis and Theoretical Modeling of the Presence and Preservation of Ice on Mars

The distribution and nature of water ice on Mars has important implications for understanding the Martian climate system, as well as evaluating the resources available for future human explorers and the astrobiological potential of our solar system. This dissertation presents a multi-faceted study of ice on Mars, combining spacecraft remote sensing datasets from imaging and radar systems with theoretical models of ice stability. In Chapter 1, I summarize the state of knowledge of ice on Mars and its relation to the planet’s climate. In Chapter 2, I present the discovery of an ice sheet in the mid-latitude region of Arcadia Planitia and constrain its properties using remote sensing observations from the Mars Reconnaissance Orbiter. In Chapter 3, I model the thermal stability and retreat from ice sheets in the mid-latitudes to understand their evolution and continued preservation to the present day. Ice in the mid-latitudes exchanges with polar ice over geologic time so to understand the other half of the Martian system, I investigate the stability of polar deposits of ice. In Chapter 4, I quantify the role of ice sublimation in the migration of troughs in the polar caps. Chapter 5 presents the conclusions of this dissertation work and puts the results in the context of outstanding questions in Mars’ climate and ice-cycle evolution

North polar trough formation due to in-situ erosion as a source of young ice in mid-latitudinal mantles on Mars

The clockwise spiral of troughs marking the Martian north polar plateau forms one of the planet's youngest megastructures. One popular hypothesis posits that the spiral pattern resulted as troughs underwent poleward migration. Here, we show that the troughs are extensively segmented into enclosed depressions (or cells). Many cell interiors display concentric layers that connect pole- and equator-facing slopes, demonstrating in-situ trough erosion. The segmentation patterns indicate a history of gradual trough growth transversely to katabatic wind directions, whereby increases in trough intersections generated their spiral arrangement. The erosional event recorded in the truncated strata and trough segmentation may have supplied up to ~25% of the volume of the mid-latitude icy mantles. Topographically subtle undulations transition into troughs and have distributions that mimic and extend the troughs' spiraling pattern, indicating that they probably represent buried trough sections. The retention of the spiral pattern in surface and subsurface troughs is consistent with the megastructure's stabilization before its partial burial. A previously suggested warm paleoclimatic spike indicates that the erosion could have occurred as recently as ~50 Ka. Hence, if the removed ice was redeposited to form the mid-latitude mantles, they could provide a valuable source of near-surface, clean ice for future human exploration

Sparse subsurface radar reflectors in Hellas Planitia, Mars

Geomorphological features potentially related to subsurface ice, such as scalloped depressions, expanded craters, pedestal craters, and banded terrain, are present in and around Hellas Planitia, Mars. We present a radar survey of the region using the Shallow Radar (SHARAD) instrument on board the Mars Reconnaissance Orbiter (MRO) to identify candidate subsurface reflectors that may be due to the presence of potentially ice-rich deposits. We found that the majority of radar returns are likely from off-nadir surface topography ("clutter"), arising from the rough topography of the region. There is no widespread radar return from any subsurface interfaces. However, we identify a group of six reflectors adjacent to each other on a plateau in Malea Patera in which we have higher confidence. Landforms associated with a likely ice-rich mantle are associated with the plateau, but the thickness of this mantle does not correspond to the expected depth of the reflectors. However, layers beneath the mantle and marginal pitting at the edge of the plateau are similar to those associated with pedestal craters, which may be ice rich and are a similar thickness to the expected depth of the reflectors. Malea Patera has been interpreted to be a volcanic caldera, so the reflectors may be associated with a volcanic deposit within the plateau, although the evidence for this is inconclusive. Because this radar detection is localized and its origin ambiguous, we cannot use it to make conclusions about the thickness of subsurface deposits in the Hellas region as a whole. The lack of widespread radar reflectors in this region, as compared to the northern mid-latitudes where extensive radar reflections have been mapped, may be due in part to higher surface roughness, which creates radar clutter that may obscure subsurface reflectors. However on the southern rim of the basin and south of the basin, the lack of reflectors may indicate that the possible ice-rich deposits observed geomorphologically in this region are too thin to be resolved by SHARAD, are dielectrically similar to the underlying unit, or have a gradual vertical transition in ice content that is not reflective for the radar. This would imply that recent climate processes may have favored widespread, thick ice deposition or preservation in the northern hemisphere as compared to the southern hemisphere.24 month embargo; published online: 12 May 2020This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

The stability of a liquid-water body below the south polar cap of Mars

Radar data from the Mars Express spacecraft show bright subsurface reflections in the Planum Australe area that could be due to liquid water located at a depth of 1.5 km (Orosei et al., 2018). If this interpretation of the data is correct, the presence of such water would have important implications for the present-day thermal state of the region. In this article, we recalculate the depth of the liquid water and we analyze the influence of the regional thermal properties in the surface heat flow and the subsurface temperatures. We have obtained a new depth to the bright reflector between 1.3 and 1.5 km by using a temperature dependent relative permittivity for the water ice and taking into account the dust content in the area. We show that regional properties in the SPLD moderately influence the thermal state of the area where the liquid water is located. A better knowledge of the porosity profile in the studied area is necessary to constrain surface heat flow and subsurface temperatures accurately. Our findings are in agreement with previous work that shows anomalously high local heat flows would be required to sustain liquid water at this location