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]

A procedure for testing the significance of orbital tuning of the martian polar layered deposits

a b s t r a c t Layered deposits of dusty ice in the martian polar caps have been hypothesized to record climate changes driven by orbitally induced variations in the distribution of incoming solar radiation. Attempts to identify such an orbital signal by tuning a stratigraphic sequence of polar layered deposits (PLDs) to match an assumed forcing introduce a risk of identifying spurious matches between unrelated records. We present an approach for evaluating the significance of matches obtained by orbital tuning, and investigate the utility of this approach for identifying orbital signals in the Mars PLDs. Using a set of simple models for ice and dust accumulation driven by insolation, we generate synthetic PLD stratigraphic sequences with nonlinear time-depth relationships. We then use a dynamic time warping algorithm to attempt to identify an orbital signal in the modeled sequences, and apply a Monte Carlo procedure to determine whether this match is significantly better than a match to a random sequence that contains no orbital signal. For simple deposition mechanisms in which dust deposition rate is constant and ice deposition rate varies linearly with insolation, we find that an orbital signal can be confidently identified if at least 10% of the accumulation time interval is preserved as strata. Addition of noise to our models raises this minimum preservation requirement, and we expect that more complex deposition functions would generally also make identification more difficult. In light of these results, we consider the prospects for identifying an orbital signal in the actual PLD stratigraphy, and conclude that this is feasible even with a strongly nonlinear relationship between stratigraphic depth and time, provided that a sufficient fraction of time is preserved in the record and that ice and dust deposition rates vary predictably with insolation. Independent age constraints from other techniques may be necessary, for example, if an insufficient amount of time is preserved in the stratigraphy

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

Summary of the Results from the Lunar Orbiter Laser Altimeter after Seven Years in Lunar Orbit

In June 2009 the Lunar Reconnaissance Orbiter (LRO) spacecraft was launched to the Moon. The payload consists of 7 science instruments selected to characterize sites for future robotic and human missions. Among them, the Lunar Orbiter Laser Altimeter (LOLA) was designed to obtain altimetry, surface roughness, and reflectance measurements. The primary phase of lunar exploration lasted one year, following a 3-month commissioning phase. On completion of its exploration objectives, the LRO mission transitioned to a science mission. After 7 years in lunar orbit, the LOLA instrument continues to map the lunar surface. The LOLA dataset is one of the foundational datasets acquired by the various LRO instruments. LOLA provided a high-accuracy global geodetic reference frame to which past, present and future lunar observations can be referenced. It also obtained high-resolution and accurate global topography that were used to determine regions in permanent shadow at the lunar poles. LOLA further contributed to the study of polar volatiles through its unique measurement of surface brightness at zero phase, which revealed anomalies in several polar craters that may indicate the presence of water ice. In this paper, we describe the many LOLA accomplishments to date and its contribution to lunar and planetary science

Science Opportunities offered by Mercury's Ice-Bearing Polar Deposits

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The fractured Moon: Production and saturation of porosity in the lunar highlands from impact cratering

We have analyzed the Bouguer anomaly (BA) of ~1200 complex craters in the lunar highlands from Gravity Recovery and Interior Laboratory observations. The BA of these craters is generally negative, though positive BA values are observed, particularly for smaller craters. Crater BA values scale inversely with crater diameter, quantifying how larger impacts produce more extensive fracturing and dilatant bulking. The Bouguer anomaly of craters larger than urn:x-wiley:00948276:media:grl53324:grl53324-math-0001 km in diameter is independent of crater size, indicating that there is a limiting depth to impact‐generated porosity, presumably from pore collapse associated with either overburden pressure or viscous flow. Impact‐generated porosity of the bulk lunar crust is likely in a state of equilibrium for craters smaller than ~30 km in diameter, consistent with an ~8 km thick lunar megaregolith, whereas the gravity signature of larger craters is still preserved and provides new insight into the cratering record of even the oldest lunar surfaces

"Now I know the terrain": phenomenological exploration of CFTs learning on evidence-based practice

Couple and family therapists are rarely the focus of research yet are critical for positive outcomes in therapy. The attempts to integrate evidence-based approaches into the practice of couple and family therapy have been controversial resulting in passionate and at times divisive dialogue. The aims of this research project were to explore what do couple and family therapists experience when learning an evidence-based approach to working with couples and families. A total of 14 couple and family therapists were interviewed about their experience with learning an evidence-based approach. The research was guided methodologically by interpretive phenomenological analysis. Three themes emerged from the participants’ experiences including: the supports and challenges in learning; the embodiment of a therapy practice; and the experience of shame while learning

Insights into lunar crustal structure and Martian climate history from surface features

Thesis: Ph. D. in Planetary Sciences, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2014.Cataloged from PDF version of thesis.Includes bibliographical references.Orbital spacecraft make observations of a planet's surface in the present day, but careful analyses of these data can yield information about deeper planetary structure and history. In this thesis, I use data sets from four orbital robotic spacecraft missions to answer longstanding questions about the crustal structure of the Moon and the climatic history of Mars. In chapter 2, I use gravity data from the Gravity Recovery and Interior Laboratory (GRAIL) mission to constrain the quantity and location of hidden volcanic deposits on the Moon. In chapter 3, I combine GRAIL data with elevation measurements from the Lunar Orbiter Laser Altimeter (LOLA) aboard the Lunar Reconnaissance Orbiter (LRO) to investigate the nature of isostatic compensation in the lunar highlands. In chapter 4, I present a new technique for analysis of the Martian polar layered deposits (PLDs). In chapter 5, I apply that technique using images of the PLDs from the MOC and HiRISE instruments aboard the Mars Global Surveyor (MGS) and Mars Reconnaissance Orbiter (MRO) to constrain their ages and deposition rates.by Michael M. Sori.Ph. D. in Planetary Science

Islands of ice on Mars and Pluto

Ice sheets, such as the polar layered deposits (PLDs) of Mars, are of great interest as records of past climate. Smaller outlier ice deposits near the north and south PLDs are likely more sensitive to climate changes and thus may hold information about more recent climate history. However, the southern outlier deposits have largely remained unmapped and unanalyzed. Here, we identify 31 deposits near, but separated from, Mars's south PLDs, all of which are located within impact craters >15 km in diameter. On the basis of morphology, radar analysis, physical similarity to portions of the PLD margin, and overall similarity to previously described deposits in Mars's north polar region, we conclude that these deposits are primarily composed of water ice. An additional 66 craters contain smaller depositional features, some of which may be remnant ice deposits. The 31 outlier ice deposits represent a previously unquantified inventory of water on Mars, with a total volume between 15,000 and 38,000 km(3). In addition, we identify five analogous outlier nitrogen ice deposits located within impact craters near Sputnik Planitia, the large nitrogen ice sheet on Pluto. Although important differences exist between Mars and Pluto, broad physical similarities between the two cases suggest that the topography and microclimates of impact craters cause them to be favorable locations for volatile accumulation and/or retention throughout the Solar System.NASA's Mars Data Analysis Program National Aeronautics & Space Administration (NASA) [80NSSC17K0510]6 month embargo; published online 15 Oct 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]