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Late development of forefoot ulcers is a common finding after transmetatarsal amputation (TMA). The primary aim of this study was to examine whether concomitant prophylactic Achilles tendon lengthening (ATL) was associated with a reduction in the incidence of forefoot ulcers postoperatively.A retrospective chart review was performed by 2 authors to identify patients who underwent TMA over a period of 5.5 years from January 1, 2015, through July 31, 2020. They identified 110 feet in 107 patients; the 83 patients (85 feet) who had ≥120 days of follow-up were used for the study. Follow-up was performed with telephone calls (80 patients) or during the last office visit (3 patients). Those who were contacted by telephone were asked if they developed an ulcer after healing from the original surgery. Mean follow-up time was 672 ± 258 days for the 30 feet with concomitant Achilles lengthening and 663 ± 434 days for the 55 feet without Achilles lengthening. Demographic data were analyzed for association with late development of forefoot ulceration.Eighty-five feet were included in the analysis. Late forefoot ulcers developed in 35% of feet that had a TMA alone (n = 55) compared with 3% of feet who received a concomitant ATL (n = 30; p0.001); the 2 groups had similar mean follow-up times. Mean time to ulcer development was 587 ± 420 days in the 19 patients without Achilles lengthening. Of the patients who developed late forefoot ulcers, 47% also developed osteomyelitis, and 16% went on to proximal amputation. Patients who developed forefoot ulcers were younger (55 ± 12 versus 63 ± 11 years of age; p = 0.006) than those who did not.ATL at the time of TMA is associated with a reduction in the risk of later development of forefoot ulcers, especially in younger patients.Therapeutic Level III . See Instructions for Authors for a complete description of levels of evidence.

Ancient Venus and Earth may have been similar in crucial ways for the development of life, such as liquid water oceans, land-ocean interfaces, favorable chemical ingredients and energy pathways. If life ever developed on, or was transported to, early Venus from elsewhere, it might have thrived, expanded and then survived the changes that have led to an inhospitable surface on Venus today. The Venus cloud layer may provide a refugium for extant life that persisted from an earlier more habitable surface environment. We introduce the Venus Life Equation - a theory and evidence-based approach to calculate the probability of extant life on Venus, L, using three primary factors of life: Origination, Robustness, and Continuity, or L = O x R x C. We evaluate each of these factors using our current understanding of Earth and Venus environmental conditions from the Archaean to the present. We find that the probability of origination of life on Venus would be similar to that of the Earth and argue that the other factors should be nonzero, comparable to other promising astrobiological targets in the solar system. The Venus Life Equation also identifies poorly understood aspects of Venus that can be addressed by direct observations with future exploration missions., Revision resubmitted after review to Astrobiology for Venus Special issue. 37 pages, 4 figures. Shorter version submitted as white paper in shortened form to Planetary and Astrobiology Decadal Survey

The interest in the possibility of life on Venus is driven not just by curiosity about life originating in another Earth-like environment, but because of the possibility that life may be playing a critical role in the planet’s present, and possibly its past, atmospheric state. The brilliance of Venus in the night sky (as viewed from Earth) is due to its highly reflective cloud cover, about 28 km thick at the equator. Its spectral albedo is about 90% at wavelengths > 500 nm, but it drops gradually to about 40% around 370 nm before rising slightly at shorter wavelengths. This albedo drop is due to the presence of several absorbers in the atmosphere and the cloud cover. A very large fraction of the energy absorbed by Venus is at ultraviolet wavelengths with sulfur dioxide above the clouds contributing to the absorption below 330 nm; however, the identities of the other absorbers remain unknown. The inability to identify the absorbers that are responsible for determining the radiative energy balance of Venus over the last century is a major impediment to understanding how the planet “works”, a major component of NASA’s efforts in planetary exploration. Limaye et al. (Astrobiology 18, 1181-1198, 2018) presented a hypothesis suggesting that cloud-based microbial life could be contributors to the spectral signatures of Venus’ clouds, building upon previous suggestions of the possibility of life in the clouds of Venus.Four interconnected themes for the exploration of Venus as an astrobiology target are: – (i) investigations focused on the likelihood that liquid water existed on the surface in the past leading to the potential for the origin and evolution of life, (ii) investigations into the potential for habitable zones within Venus’ clouds and Venus-like atmospheres, (iii) theoretical investigations into how active aerobiology may impact the radiative energy balance of Venus’ clouds and Venus-like atmospheres, and (iv) application of these investigative themes towards better understanding the atmospheric dynamics and habitability of exoplanets. These themes can serve as a basis for proposed Venus Astrobiology Objectives and suggestions for measurements for future missions, as per the goals and objectives developed by the Venus Exploration Analysis Group (VEXAG), which is sponsored by NASA to plan for the future exploration of Venus. A Venus Collection to be published in Astrobiology journal in 2021 will include papers from the “Habitability of the Venus Cloud Layer”, Moscow (October 2019) workshop.

International audience; More than 85% of the 23 investigations developed by VEXAG are largely accomplished via a NF mission centered on a variable-altitude balloon (aerobot) supported by a science/comm orbiter. Circling Venus >15 times over ~90 days, the aerobot repeatedly visits 52-62 km alts as it semi-continuously samples a host of environmental & surface parameters.

Understanding Venus will benefit from a dedicated effort through an international program of missions that are coordinated and offering opportunities for coooperation. The recent discovery of phosphene in the Venus clouds and possibility of life will increase the exploration missions and cooperation and coordination will be very benefical.

We present a case for the exploration of Venus as an astrobiology target—(1) investigations focused on the likelihood that liquid water existed on the surface in the past, leading to the potential for the origin and evolution of life, (2) investigations into the potential for habitable zones within Venus’ present-day clouds and Venus-like exo atmospheres, (3) theoretical investigations into how active aerobiology may impact the radiative energy balance of Venus’ clouds and Venus-like atmospheres, and (4) application of these investigative approaches toward better understanding the atmospheric dynamics and habitability of exoplanets. The proximity of Venus to Earth, guidance for exoplanet habitability investigations, and access to the potential cloud habitable layer and surface for prolonged in situ extended measurements together make the planet a very attractive target for near term astrobiological exploration.

Haglund's syndrome is impingement of the retrocalcaneal bursa and Achilles tendon caused by a prominence of the posterosuperior calcaneus. Radiographic measurements are not sensitive or specific for diagnosing Haglund's deformity. Localization of a bone deformity and tendinopathy in the same sagittal section of a magnetic resonance imaging scan can assist with the diagnosis in equivocal cases. The aim of the present cross-sectional study was to determine the prevalence of Haglund's syndrome in patients presenting with Achilles tendinopathy and note any associated findings to determine the criteria for a diagnosis of Haglund's syndrome. We reviewed 40 magnetic resonance imaging scans with Achilles tendinopathy and 19 magnetic resonance imaging scans with Achilles high-grade tears and/or ruptures. Achilles tendinopathy was often in close proximity to the superior aspect of the calcaneal tuberosity, consistent with impingement (67.5%). Patients with Achilles impingement tendinopathy were more often female (p

Planetary-scale waves are thought to play a role in powering the yet-unexplained atmospheric superrotation of Venus. Puzzlingly, while Kelvin, Rossby and stationary waves manifest at the upper clouds (65--70 km), no planetary-scale waves or stationary patterns have been reported in the intervening level of the lower clouds (48--55 km), although the latter are probably Lee waves. Using observations by the Akatsuki orbiter and ground-based telescopes, we show that the lower clouds follow a regular cycle punctuated between 30$^{\circ}$N--40$^{\circ}$S by a sharp discontinuity or disruption with potential implications to Venus's general circulation and thermal structure. This disruption exhibits a westward rotation period of $\sim$4.9 days faster than winds at this level ($\sim$6-day period), alters clouds' properties and aerosols, and remains coherent during weeks. Past observations reveal its recurrent nature since at least 1983, and numerical simulations show that a nonlinear Kelvin wave reproduces many of its properties., Comment: 21 pages, 10 figures, 2 animated figures and 2 tables

Basilar opening and closing wedge osteotomies are generally utilized in patients with high intermetatarsal angles. The basilar closing osteotomy has fallen out of favor due to concerns regarding dorsiflexion malunions, consistency of correction, and shortening. Closing wedge osteotomies should be avoided in patients with pronation of the first metatarsal or high proximal articular set angles (PASA). The basilar opening osteotomy has become more popular in recent years due to locking plate fixation with high union rates, although with particular complications. Opening wedge osteotomies should be avoided in patients with significant pronation of the first metatarsal, high PASA, and positive metatarsal protrusion distances because the osteotomy increases the length of the first metatarsal. Basilar wedge osteotomies have a high learning curve and are associated with higher complication rates in meta-analysis. Basilar wedge osteotomies require precision of the osteotomy to avoid over- or under correction.

We show that a spacecraft launched from Earth towards Mars following a Hohmann minimum energy transfer trajectory has a strong tendency to remain well-connected magnetically to Earth, in the early phase of the transfer, or to Mars in the late phase, via the Parker spiral magnetic field. On the return trip, the spacecraft would remain reasonably well-connected magnetically first to Mars and later to Earth. Moreover, good magnetic connectivity occurs on all Hohmann transfers between neighboring planets in the inner solar system out to Mars. We call this hitherto unnamed circumstance the Hohmann–Parker effect. We show consequences of the effect by means of simultaneous cosmic radiation proxy observations made near Earth, near Mars, and at the Mars Science Laboratory on the transfer from Earth to Mars in 2011/2012. We support the observations with simulations of the large-scale magnetic field of the inner heliosphere during this period and compare the results with our predictions. The implications of the Hohmann–Parker effect are discussed. & 2013 Published by Elsevier Ltd.

Noninsertional Achilles tendinopathy often responds to nonoperative treatment. When nonoperative treatment fails, the clinician must distinguish between paratendinopathy and noninsertional tendinopathy. In paratendinopathy, myofibroblasts synthesize collagen, causing adhesions, and the paratenon may be released or excised. If a core area of tendinopathy is identified on MRI, the area is excised longitudinally and repaired with a side-to-side suture. If greater than 50% of the tendon diameter is excised, the authors recommend a short flexor hallucis longus tendon transfer with an interference screw. A turndown flap of the gastrocnemius aponeurosis is also described with good results.

The equilibrium suggested as a buffer for CO2 in the Venus atmosphere, CaCO3 + SiO2 = CaSiO3 + CO2, cannot act as a buffer at the Venus surface/troposphere – the pressure–temperature slope of the equilibrium and that of the atmosphere (dry adiabat with significant greenhouse heating) do not provide buffering capacity (if indeed CaCO3 were present). Instead, perturbations to T or P(CO2) can produce catastrophic expansion or collapse of the atmosphere. This instability can be generalized to all devolatilization reactions that produce a radiatively active gas in a planetary atmosphere dominated by such gases, and gives a simple thermochemical criterion for whether a reaction could buffer such an atmosphere. Simple decarbonation reactions fail this criterion, suggesting that the abundance of CO2 in a CO2-dominated atmosphere cannot be buffered by chemical reactions with the surface; a similar conclusion holds for the abundance of H2O in an H2O-dominated (steam) atmosphere. Buffering of minor gases is more likely; a mineral buffer equilibrium for SO2 proposed for Venus, FeS2 + CO2 = Fe3O4 + SO2 + CO, passes the thermochemical criterion, as does a reaction involving Ca sulfate. These inferences can be generalized to atmospheres in ‘moist’ adiabatic equilibria, and to extrasolar Venus-like planets, and will help in interpreting the compositions of their atmospheres.

We measured the 1 mHz-1 MHz electrical properties of ice-hydrate binary systems formed from solutions of NaCl, CaCl(2), and MgSO(4), with supplementary measurements of HCl. Below the eutectic temperature, electrical parameters are well described by mixing models in which hydrate is always the connected phase. Above the eutectic temperature, a salt concentration threshold of approximately 3 mM in the initial solution is required for the unfrozen brine fraction to form interconnected, electrically conductive networks. The dielectric relaxation frequency for saline ice increases with increasing impurity content until Cl(-) reaches saturation. Because there is insufficient H(3)O(+) for charge balance, salt cations must be accommodated interstitially in the ice. Dielectric relaxations near the ice signature were identified for CaCl(2).6H(2)O and MgSO(4).11H(2)O but not for NaCl.2H(2)O. Ionic and L-defect concentrations in salt hydrates up to approximately 10(-4) and 10(-3) per H(2)O molecule, respectively, follow from the electrical properties, Jaccard theory, and the assumption that protonic-defect mobilities are similar to ice. These high defect concentrations-up to a few orders of magnitude greater than saturation values in ice-indicate that intrinsic disruption of hydrogen bonding in salt hydrates is common.

We present a map of the global mean lower cloud coverage of Venus. This map is the average of 35 nights of 2.26 μm night side observations taken at NASA's Infrared Telescope Facility on Mauna Kea, over the years spanning 2001–2007. The atmosphere of Venus is a very dynamic system, and the lower clouds are constantly changing [Crisp, D., Allen, D.A., Grinspoon, D.H., Pollack, J.B., 1991a. The dark side of Venus: near-infrared images and spectra from the Anglo-Australian Observatory. Science, 253, 1263–1266]. By studying average cloud coverage, the daily variations are suppressed in order to see the underlying persistent cloud pattern. We find a relatively thick but highly variable equatorial band of clouds (±20° in latitude) and more quiescent mid-latitude clouds that are less opaque on average, with persistent cloudiness near the poles. We show that there is enough variation between our daily observations or between observations taken in different months that they cannot be considered individually representative of the global mean. We also compare the cloud coverage map to the topography of Venus and find no definitive correlations with high altitude features.

We developed a numerical model to assess the lithoautotrophic habitability of Mars based on metabolic energy, nutrients, water availability, and temperature. Available metabolic energy and nutrient sources were based on a laboratory-produced Mars-analog inorganic chemistry. For this specific reference chemistry, the most efficient lithoautotrophic microorganisms would use Fe(2+) as a primary metabolic electron donor and NO(3)(-) or gaseous O(2) as a terminal electron acceptor. In a closed model system, biomass production was limited by the electron donor Fe(2+) and metabolically required P, and typically amounted to approximately 800 pg of dry biomass/ml ( approximately 8,500 cells/ml). Continued growth requires propagation of microbes to new fecund environments, delivery of fresh pore fluid, or continued reaction with the host material. Within the shallow cryosphere--where oxygen can be accessed by microbes and microbes can be accessed by exploration-lithoautotrophs can function within as little as three monolayers of interfacial water formed either by adsorption from the atmosphere or in regions of ice stability where temperatures are within some tens of degrees of the ice melting point. For the selected reference host material (shergottite analog) and associated inorganic fluid chemistry, complete local reaction of the host material potentially yields a time-integrated biomass of approximately 0.1 mg of dry biomass/g of host material ( approximately 10(9) cells/g). Biomass could also be sustained where solutes can be delivered by advection (cryosuction) or diffusion in interfacial water; however, both of these processes are relatively inefficient. Lithoautotrophs in near-surface thin films of water, therefore, would optimize their metabolism by deriving energy and nutrients locally. Although the selected chemistry and associated model output indicate that lithoautotrophic microbial biomass could accrue within shallow interfacial water on Mars, it is likely that these organisms would spend long periods in maintenance or survival modes, with instantaneous biomass comparable to or less than that observed in extreme environments on Earth.

Several observations indicate that the cloud deck of the venusian atmosphere may provide a plausible refuge for microbial life. Having originated in a hot proto-ocean or been brought in by meteorites from Earth (or Mars), early life on Venus could have adapted to a dry, acidic atmospheric niche as the warming planet lost its oceans. The greatest obstacle for the survival of any organism in this niche may be high doses of ultraviolet (UV) radiation. Here we make the argument that such an organism may utilize sulfur allotropes present in the venusian atmosphere, particularly S(8), as a UV sunscreen, as an energy-converting pigment, or as a means for converting UV light to lower frequencies that can be used for photosynthesis. Thus, life could exist today in the clouds of Venus.

Climate-interior coupled evolution is investigated for Venus by merging a partial-melting/parameterized mantle convection model with a gray radiative-convective atmospheric model. A positive feedback process can operate by the release of water to the atmosphere via mantle melting, leading to an increase in atmospheric opacity and the radiative temperature gradient. The resulting amplification of the greenhouse surface temperature raises the mantle temperature leading to an increase in the partial-melting rate. Using thin-lid convection, a coupled model for Venus running over an interval of 3 to 1 Ga shows a significant increase in surface temperature, partial-melting extent, and extrusive magma flux compared to a model where there is no communication between greenhouse-modulated surface temperature and partial-melting in the interior. Coupled and uncoupled models that transition (with variable timing) to stagnant-lid convection either shut down partial melting via lithospheric thickening, or evolve to large amounts of melt due to increased interior temperatures.

The present climate of Venus is controlled by an efficient carbon dioxide‐water greenhouse effect and by the radiative properties of its global cloud cover. Both the greenhouse effect and clouds are sensitive to perturbations in the abundance of atmospheric water vapor and sulfur gases. Planetary-scale processes involving the release, transport, and sequestering of volatiles affect these abundances over time, driving changes in climate. We have developed a numerical model of the climate evolution of Venus. Atmospheric temperatures are calculated using a one-dimensional two-stream radiative‐convective model that treats the transport of thermal infrared radiation in the atmosphere and clouds. These radiative transfer calculations are the first to utilize high-temperature, high-resolution spectral databases for the calculation of infrared absorption and scattering in Venus’ atmosphere. We use a chemical/microphysical model of Venus’ clouds to calculate changes in cloud structure that result from variations in atmospheric water and sulfur dioxide. Atmospheric abundances of water, sulfur dioxide, and carbon dioxide change under the influence of the exospheric escape of hydrogen, outgassing from the interior, and heterogeneous reactions with surface minerals. Radar images from the Magellan mission show that the surface of Venus has been geologically active on a global scale, yet its sparse impact cratering record is almost pristine. This geologic record on Venus is consistent with an epoch of rapid plains emplacement 600‐ 1100 Myr ago. Our models show that intense volcanic outgassing of sulfur dioxide and water during this time would have resulted in the formation of massive sulfuric acid/water clouds and the cooling of the surface for 100‐300 Myr. The thick clouds would have subsequently given way to high, thin water clouds as atmospheric sulfur dioxide was lost to reactions with the surface. Surface temperatures approaching 900 K would have been reached 200‐500 Myr after the onset of volcanic resurfacing. Evolution to current conditions would have proceeded due to loss of atmospheric water at the top of the atmosphere, ongoing low-level volcanism, and the reappearance of sulfuric acid/water clouds. We find that the maintenance of sulfuric acid/water clouds on Venus today requires sources of outgassed sulfur active in the past 20‐50 Myr, in contrast with the 1.9 Myr as determined from geochemical arguments alone (B. Fegley and R. G. Prinn 1989, Nature 337, 55‐58). c ∞ 2001 Academic Press

Evaporite deposits may represent significant sinks of mobile cations (e.g., those of Ca, N, Mg, and Fe) and anions (e.g., those of C, N, S, and Cl) among the materials composing the Martian surface and upper crust. Carbon and nitrogen are especially interesting because of their role as atmospheric gases which can become incorporated into crustal rocks. However, the nature of evaporite precursor brines formed under Martian conditions is poorly understood. To date, only a very limited number of laboratory investigations have been reported which have any bearing on a better understanding of various processes related to brine or evaporite formation on Mars. Here we report on preliminary laboratory experiments that exposed igneous minerals analogous to those in Martian (Shergottites, Nakhlites, and Chassigny (SNC) group) meteorites to a simulated Martian atmosphere and pure, deoxygenated water. Analysis of the water over intervals of time approaching 1 year showed that atmospheric gases dissolved to form carbonate and nitrate ions while minerals dissolved to form sulfate and chloride along with various cations. On an annual basis, ion formation gave a carbonate/sulfate ratio that is comparable to the ratio found among salts in SNC meteorites. The sulfate/chloride ratio of the experimental brines is higher than in SNC meteorites but lower than in surface soils measured at the Viking and Pathfinder landing sites.

H 2 O, CO 2 , SO 2 , O 2 , H 2 , H 2 S, HCl, chlorinated hydrocarbons, NO, and other trace gases were evolved during pyrolysis of two mudstone samples acquired by the Curiosity rover at Yellowknife Bay within Gale crater, Mars. H 2 O/OH-bearing phases included 2:1 phyllosilicate(s), bassanite, akaganeite, and amorphous materials. Thermal decomposition of carbonates and combustion of organic materials are candidate sources for the CO 2 . Concurrent evolution of O 2 and chlorinated hydrocarbons suggests the presence of oxychlorine phase(s). Sulfides are likely sources for sulfur-bearing species. Higher abundances of chlorinated hydrocarbons in the mudstone compared with Rocknest windblown materials previously analyzed by Curiosity suggest that indigenous martian or meteoritic organic carbon sources may be preserved in the mudstone; however, the carbon source for the chlorinated hydrocarbons is not definitively of martian origin.

International audience; The Radiation Assessment Detector (RAD) on the Mars Science Laboratory's Curiosity rover began making detailed measurements of the cosmic ray and energetic particle radiation environment on the surface of Mars on 7 August 2012. We report and discuss measurements of the absorbed dose and dose equivalent from galactic cosmic rays and solar energetic particles on the martian surface for similar to 300 days of observations during the current solar maximum. These measurements provide insight into the radiation hazards associated with a human mission to the surface of Mars and provide an anchor point with which to model the subsurface radiation environment, with implications for microbial survival times of any possible extant or past life, as well as for the preservation of potential organic biosignatures of the ancient martian environment.

The climate of Venus is to a large degree controlled by the radiative properties of its massive atmosphere. However, volcanic outgassing and surface-atmosphere interactions may moderate the atmospheric abundances of CO2 and other radiatively important volatiles. Recently, work on the interpretation of the impact cratering record has placed limits on the magnitude of the volcanic flux. Additionally, recent laboratory data on the equilibria and kinetics of possible surface-atmosphere reactions under Venus-like conditions provide important insights into the role that they may play in moderating Venus' climate. The surface temperature and pressure on Venus coincide approximately with the P-T equilibrium of the calcite-wollastonite mineral reaction, and atmospheric sulfur species are probably involved in rapid heterogeneous reactions with the surface. Perturbations to the atmospheric inventory of radiatively active species may have a significant impact on the climate of Venus and upon the stability of the greenhouse effect. Through the use of a Venus climate model that couples atmospheric radiative-convective equilibrium with surface processes, we show that it is likely that Venus' climate is at or near a state of unstable equilibrium. Furthermore, we show that only moderate perturbations in the abundances of radiatively active volatiles may be sufficient to precipitate changes to new climate regimes.

The early development of life, a fundamental question for humankind, requires the presence of a suitable planetary climate. Our understanding of how habitable planets come to be begins with the worlds closest to home. Venus, Earth, and Mars differ only modestly in their mass and distance from the Sun, yet their current climates could scarcely be more divergent. Only Earth has abundant liquid water, Venus has a runaway greenhouse, and evidence for life-supporting conditions on Mars points to a bygone era. In addition, an Earth-like hydrologic cycle has been revealed in a surprising place: Saturn's cloud-covered satellite Titan has liquid hydrocarbon rain, lakes, and river networks. Deducing the initial conditions for these diverse worlds and unravelling how and why they diverged to their current climates is a challenge at the forefront of planetary science. Through the contributions of more than sixty leading experts in the field, Comparative Climatology of Terrestrial Planets sets forth the foundations for this emerging new science and brings the reader to the forefront of our current understanding of atmospheric formation and climate evolution. Particular emphasis is given to surface-atmosphere interactions, evolving stellar flux, mantle processes, photochemistry, and interactions with the interplanetary environment, all of which influence the climatology of terrestrial planets. From this cornerstone, both current professionals and most especially new students are brought to the threshold, enabling the next generation of new advances in our own solar system and beyond.

The Radiation Assessment Detector (RAD) on the Mars Science Laboratory (MSL) is an energetic particle detector designed to measure a broad spectrum of energetic particle radiation. It will make the first-ever direct radiation measurements on the surface of Mars, detecting galactic cosmic rays, solar energetic particles, secondary neutrons, and other secondary particles created both in the atmosphere and in the Martian regolith. The radiation environment on Mars, both past and present, may have implications for habitability and the ability to sustain life. Radiation exposure is also a major concern for future human missions. The RAD instrument combines charged- and neutral-particle detection capability over a wide dynamic range in a compact, low-mass, low-power instrument. These capabilities are required in order to measure all the important components of the radiation environment. RAD consists of the RAD Sensor Head (RSH) and the RAD Electronics Box (REB) integrated together in a small, compact volume. The RSH contains a solid-state detector telescope with three silicon PIN diodes for charged particle detection, a thallium doped Cesium Iodide scintillator, plastic scintillators for neutron detection and anti-coincidence shielding, and the front-end electronics. The REB contains three circuit boards, one with a novel mixed-signal ASIC for processing analog signals and an associated control FPGA, another with a second FPGA to communicate with the rover and perform onboard analysis of science data, and a third board with power supplies and power cycling or “sleep”-control electronics. The latter enables autonomous operation, independent of commands from the rover. RAD is a highly capable and highly configurable instrument that paves the way for future compact energetic particle detectors in space.

The range of surface ages on Venus and the rate of recent volcanism are two major questions that can be addressed through an analysis of Magellan images. We report on a 3-D Monte Carlo resurfacing model that seeks to explain the resurfacing history of Venus by simulating the evolving surface under the competing processes of impact cratering and volcanism. By incorporating the observed size distribution of volcanic forms on Venus, and the assumptions of constant volcanic and impactor fluxes, we seek a solution that is consistent with the observed impact crater population. In the Monte Carlo simulations, a volcanic flux of 0.37 km3/yr, operating for 550 m.y. on initially craterless surfaces, yields surfaces that are statistically similar to Venus'. It is shown that the statistics of the impact cratering record are inconsistent with an equilibrium resurfacing model.

Based on a review of factors associated with Separation Anxiety Disorder (SAD), this article attempts to show how an understanding of these factors can be helpful in instances of separation anxiety in missionary children (MKs). Using the example of one MK who exhibited major criteria for SAD diagnosis as a result of being sent away to boarding school, the article illustrates various psychodynamically and behaviorally oriented intervention strategies. The interventions are evaluated and implications suggested for parents of MKs, boarding school houseparents, and other staff, as well as mission administrators.

Evaporite-rich sedimentary deposits on Mars were formed under chemical conditions quite different from those on Earth. Their unique chemistries record the chemical and aqueous conditions under which they were formed and possibly subsequent conditions to which they were subjected. We have produced evaporite salt mineral suites in the laboratory under two simulated Martian atmospheres: (1) present-day and (2) a model of an ancient Matian atmosphere rich in volcanic gases. The composition of these synthetic Mars evaporites depends on the atmospheres under which they were desiccated as well as the chemistries of their precursor brines. In this report, we describe a Mars analog evaporite laboratory apparatus and the experimental methods we used to produce and analyze the evaporite mineral suites.

[1] Thermal radiation within Venus atmosphere is analyzed in close details. Prominent features are identified, which are then used to design a parameterization (a highly simplified and yet accurate enough model) to be used in General Circulation Models. The analysis is based on a net exchange formulation, using a set of gaseous and cloud optical data chosen among available referenced data. The accuracy of the proposed parameterization methodology is controlled against Monte Carlo simulations, assuming that the optical data are exact. Then, the accuracy level corresponding to our present optical data choice is discussed by comparison with available observations, concentrating on the most unknown aspects of Venus thermal radiation, namely the deep atmosphere opacity and the cloud composition and structure.

NASA’s Planetary Science Division recently commissioned a Science and Technology Definition Team to design a potential Venus Flagship mission. The team developed a list of various mission elements that could serve as parts of an overall mission architecture, including orbiters, balloons at various altitudes, and landed platforms of varying number and lifetime. In order to determine the mission architecture that provided the best science within the desired cost range, teams of scientists developed priorities for the science investigations previously detailed by the Venus Exploration Assessment Group (VEXAG). By categorizing the suitability of mission elements to achieve the science investigations, it was possible to construct a Science Figure of Merit (FOM) that could be used to rate the mission elements in terms of their overall science capability. Working in parallel, a team of technologists and engineers identified the technologies needed for the different mission elements, as well as their technology readiness. A Technology FOM was then created reflecting the criticality of a specific technology as well as its technology readiness level. When the Science and Technology FOMs were combined with a rapid costing approach previous developed, it became possible to rapidly evaluate not only individual mission elements, but also their combinations into various mission architectures, accelerating the convergence on a flagship mission architecture that provided the best science within the flagship mission budget, as well as reducing reliance on unproven technology..

A terrestrial stratospheric telescope is ideally suited for making infrared observations of Venus' night hemisphere during inferior conjunctions. The near-space environment at 35 km altitude has low daytime sky backgrounds and lack of atmospheric turbulence, both of which are necessary for observing Venus' night side at the diffraction limit when Venus is close to the Sun. In addition, the duration of the observing campaign will be around 3 weeks, a time period that is achievable by current long duration flights. The most important advantage, however, will be the ability of a balloonborne telescope to clearly image Venus' night side continuously throughout a 12-hr period (more for certain launch site latitudes), a capability that cannot be matched from the ground or from the Venus Express spacecraft currently in orbit around Venus. Future missions, such as the Japanese Venus Climate Orbiter will also not be able to achieve this level of synoptic coverage. This capability will provide a detailed, continuous look at evolving cloud distributions in Venus' middle and lower cloud decks through atmospheric windows at 1.74 and 2.3 μm, which in turn will provide observational constraints on models of Venus' circulation. The science requirements propagate to several aspects of the telescope: a 1.4-m aperture to provide a diffraction limit of 0.3" at 1.74 μm (to improve upon non-AO ground-based resolution by a factor of 2); a plate scale of 0.1" per pixel, which in turn requires an f/15 telescope for 13 μm pixels; pointing and stability at the 0.05" level; stray light baffling; a field of view of 2 arc minutes; ability to acquire images at 1.26, 1.74 and 2.3 μm; and ability to operate aloft for three weeks at a time. The specific implementations of these requirements are outlined in this paper. Briefly, a 1.4-m Gregorian telescope is proposed, with stray light baffling at the intermediate focus. A three-stage pointing system is described, consisting of a coarse azimuthal rotator, a moderate pointing system based on a star tracker and ALT/AZ gimbals, and a fine pointing system based on analog photodiodes and a fine steering mirror. The science detectors are not discussed here, except to specify the requirement for moderate resolution (R > 1000) spectroscopy.

Astronomical balloon-borne telescopes have the potential to improve seeing over ground-based telescopes, but are compromised by their instability. A one-meter telescope in the Earth's stratosphere could achieve diffraction-limited seeing superior to the performance of any ground-based telescope in optical or UV wavelengths. If the stability issues could be addressed, such a telescope could be used for a variety of scientific purposes, including high- resolution optical imaging, or infrared imaging of targets that are usually precluded from ground-based systems, such as Jupiter, Saturn or Venus. An image stabilization system was developed with the goal of maintaining the position of the image to within 0.1 arcseconds on the focal plane during image acquisition. This effort requires both deriving an error signal and applying that error signal to a corrective element. Using a control loop with an optical reference provides a greater bandwidth than an inertial reference and improves control of high frequency vibrations. The control feedback signal was generated by monitoring the position of an image using a lateral effect cell. A fine steering mirror was used as a diagonal flat to control the position of the image and correct for small disturbances in pointing. To evaluate the system, vibration was induced in a synthetic image and the resultant motion of the image measured. The system was implemented and tested on a 14-inch f/10 Schmidt-Cassegrain telescope. Large disturbances were attenuated by a factor of 10-100, with a noise level of less than 2 arcseconds on the test telescope.

[1] Widespread, massive layered sediments, studied by surface rovers and Mars-orbiting spectrometers, are found to be rich in sulfates. No similarly massive carbonates have been detected. We present the results of coupled atmospheric and geochemical calculations of the formation of the sulfate-rich Meridiani sediments, and offer an explanation for why extensive layered carbonates are not found there or elsewhere on Mars. Large scale volcanism from the build-up of Tharsis during the late Noachian would have injected large amounts of SO2 into the atmosphere. Efficient photochemical conversion of SO2 to H2SO4 would have caused widespread sulfuric acid/water clouds, similar to those seen on Venus today. Precipitation from these clouds and acidification of surface water would have sustained a thick, warm CO2 atmosphere via carbonate inhibition. Such an atmosphere could have been subjected to loss to space via impact erosion and sputtering. Once atmospheric SO2 gas production dropped and waters become more alkaline, the remaining CO2 in the atmosphere collapsed to form poorly consolidated carbonate patinas on rock surfaces and in open fractures.

This chapter reviews the observations of the radiative fluxes inside and outside the Venusian atmosphere, along with the available data about the planetary energy balance and the distribution of sources and sinks of radiative energy. We also briefly address the role of the heat budget on the atmospheric temperature structure, global circulation, thermodynamics, climate and evolution. We compare the main features of radiative balance on the terrestrial planets, and provide a general description of the radiative-convective equilibrium models used to study their atmospheres. We describe the physics of the greenhouse effect as it applies to the evolution of the Venusian climate, concluding with a summary of outstanding open issues.

For hundreds of years prior to the space age, Venus was considered among the most likely homes for extraterrestrial life. Since planetary exploration began, Venus has not been considered a promising target for Astrobiological exploration. However, Venus should be central to such an exploration program for several reasons. At present Venus is the only other Earth-sized terrestrial planet that we know of, and certainly the only one we will have the opportunity to explore in the foreseeable future. Understanding the divergence of Earth and Venus is central to understanding the limits of habitability in the inner regions of habitable zones around solar-type stars. Thus Venus presents us with a unique opportunity for putting the bulk properties, evolution and ongoing geochemical processes of Earth in a wider context. Many geological and meteorological processes otherwise active only on Earth at present are currently active on Venus. Active volcanism most likely affects the climate and chemical equilibrium state of the atmosphere and surface, and maintains the global cloud cover. Further, if we think beyond the specifics of a particular chemical system required to build complexity and heredity, we can ask what general properties a planet must possess in order to be considered a possible candidate for life. The answers might include an atmosphere with signs of flagrant chemical disequilibrium and active, internally driven cycling of volatile elements between the surface, atmosphere and interior. At present, the two planets we know of which possess these characteristics are Earth and Venus. Venus almost surely once had warm, habitable oceans. The evaporation of these oceans, and subsequent escape of hydrogen, most likely resulted in an oxygenated atmosphere. The duration of this phase is poorly understood, but during this time the terrestrial planets were not isolated. Rather, due to frequent impact transport, they represented a continuous environment for early microbial life. Life, once established in the early oceans of Venus, may have migrated to the clouds which, on present day Venus, may represent a habitable niche. Though highly acidic, this aqueous environment enjoys moderate temperatures, surroundings far from chemical equilibrium, and potentially useful radiation fluxes. Observations of unusual chemistry in the clouds, and particle-populations that are not well characterized, suggest that this environment must be explored much more fully before biology can be ruled out. A sulfur-based metabolism for cloud-based life on Venus has recently been proposed (Schulze-Makuch et al., 2004). While speculative, these arguments, along with the discovery of terrestrial extremophile organisms that point toward the plausibility of survival in the Venusian clouds, establish the credibility of astrobiological exploration of Venus. Arguments for the possible existence of life on Mars or Europa are, by convention and repetition, seen as more mainstream than arguments for life elsewhere, but their logical status is similar to plausibility arguments for life on Venus. With the launch of COROT in 2006 and Kepler in 2008 the demographics of Earth-sized planets in our galaxy should finally become known. Future plans for a Terrestrial Planet Finder or Darwin-type space-based spectrograph should provide the capability of studying the atmospheric composition and other properties of terrestrial planets. One of the prime rationales for building such instruments is the possibility of identifying habitable planets or providing more generalized observational constraints on the habitable zones of stellar systems. Given the prevalence of CO 2 dominated atmospheres in our own solar system, it is quite likely that a large fraction of these will be Venus-like in composition and evolutionary history. We will be observing these planets at random times in their evolution. In analogy with our own solar system, it is just as likely that we will find representatives of early Venus and early Earth type planets from the first 2 billion years of their evolution as it is that we will find "mature Venus" and "mature Earth" type planets that are roughly 4.5 billion years old. Therefore, in order to be poised to use the results of these future observations of extrasolar planets to make valid, generalized inferences about the size, shape and evolution of stellar habitable zones it is vital that we obtain a much deeper understanding of the evolutionary histories and divergence of Earth and Venus. The Mars Exploration Rover findings of evidence for aqueous conditions on early Mars have intensified interest in the possible origin and evolution of life on early Mars. Yet the evidence suggests that these deposits were formed in a highly acidic and sulfur-rich environment. During this phase, Mars may well have had sulfuric acid clouds sustained by vigorous, sulfur-rich volcanism. This suggests that a greater understanding of the chemistry of the Venusian atmosphere and clouds, and surface/atmosphere interactions, may help to characterize the environment of Mars when life may have formed there. In turn, if signs of early life are found on Mars during the upcoming decades of intensive astrobiological exploration planned for that planet, it will strengthen arguments for the plausibility of life in an early and gradually acidifying Venusian environment. Of our two neighboring planets, Venus and Mars, it is not yet known which held on to its surface oceans, and early habitable conditions, for longer.

[1] We report on laboratory experiments in which we allowed an SNC-analog mineral mixture to react with water under a simulated Mars atmosphere containing the added gases SO2, HCl and NO2. The addition of acidic gases was designed to simulate the atmospheric effects of periods of increased volcanic activity on Mars. The S/Cl ratio in our experimental brines was about 200, compared with an average value of approximately 5 measured in martian fines at the Mars Pathfinder and Viking 1 and 2 landing sites. This suggests that if salts were produced under an atmosphere higher in acidic volatiles than at present, they would have produced evaporite deposits higher in S than is presently found in the martian fines. Erosion of these high-sulfur evaporites and mixing with eroded mafic basalts could have produced the globally homogenous, salt-rich mobile fines that are present on Mars today.

Tectonics, volcanism, and climate on Venus may be strongly coupled. Large excursions in surface temperature predicted to follow a global or near-global volcanic event diffuse into the interior and introduce thermal stresses of a magnitude sufficient to influence widespread tectonic deformation. This sequence of events accounts for the timing and many of the characteristics of deformation in the ridged plains of Venus, the most widely preserved volcanic terrain on the planet.

We report on laboratory experiments which simulate the breakdown of organic compounds under Martian surface conditions. Chambers containing Mars-analog soil mixed with the amino acid glycine were evacuated and filled to 100 mbar pressure with a Martian atmosphere gas mixture and then irradiated with a broad spectrum Xe lamp. Headspace gases were periodically withdrawn and analyzed via gas chromatography for the presence of organic gases expected to be decomposition products of the glycine. The quantum efficiency for the decomposition of glycine by light at wavelengths from 2000 to 2400 angstroms was measured to be 1.46 +/- 1.0 x 10(-6) molecules/photon. Scaled to Mars, this represents an organic destruction rate of 2.24 +/- 1.2 x 10(-4) g of C m-2 yr-1. We compare this degradation rate with the rate that organic compounds are brought to Mars as a result of meteoritic infall to show that organic compounds are destroyed on Mars at rates far exceeding the rate that they are deposited by meteorites. Thus the fact that no organic compounds were found on Mars by the Viking Lander Gas Chromatograph Mass Spectrometer experiment can be explained without invoking the presence of strong oxidants in the surface soils. The organic destruction rate may be considered as an upper bound for the globally averaged biomass production rate of extant organisms at the surface of Mars. This upper bound is comparable to the slow growing cryptoendolithic microbial communities found in dry Antarctica deserts. Finally, comparing these organic destruction rates to recently reported experiments on the stability of carbonate on the surface of Mars, we find that organic compounds may currently be more stable than calcite.

Information is pouring in about Mars. These are thrilling times for those who are proposing — and challenging — ideas about the chemical evolution of the planet and its potential for having harboured life.

The Viking Gas Chromatograph Mass Spectrometer failed to detect organic compounds on Mars, and both the Viking Labeled Release and the Viking Gas Exchange experiments indicated a reactive soil surface. These results have led to the widespread belief that there are oxidants in the martian soil. Since H2O2 is produced by photochemical processes in the atmosphere of Mars, and has been shown in the laboratory to reproduce closely the Viking LR results, it is a likely candidate for a martian soil oxidant. Here, we report on the results of a coupled soil/atmosphere transport model for H2O2 on Mars. Upon diffusing into the soil, its concentration is determined by the extent to which it is adsorbed and by the rate at which it is catalytically destroyed. An analytical model for calculating the distribution of H2O2 in the martian atmosphere and soil is developed. The concentration of H2O2 in the soil is shown to go to zero at a finite depth, a consequence of the nonlinear soil diffusion equation. The model is parameterized in terms of an unknown quantity, the lifetime of H2O2 against heterogeneous catalytic destruction in the soil. Calculated concentrations are compared with a H2O2 concentration of 30 nmoles/cm3, inferred from the Viking Labeled Release experiment. A significant result of this model is that for a wide range of H2O2 lifetimes (up to 10(5) years), the extinction depth was found to be less than 3 m. The maximum possible concentration in the top 4 cm is calculated to be approximately 240 nmoles/cm3, achieved with lifetimes of greater than 1000 years. Concentrations higher than 30 nmoles/cm3 require lifetimes of greater than 4.3 terrestrial years. For a wide range of H2O2 lifetimes, it was found that the atmospheric concentration is only weakly coupled with soil loss processes. Losses to the soil become significant only when lifetimes are less than a few hours. If there are depths below which H2O2 is not transported, it is plausible that organic compounds, protected from an oxidizing environment, may still exist. They would have been deposited by meteors, or be the organic remains of past life.

The National Science Foundation's (NSF) Research Experience for Undergraduates (REU) program provides undergraduate students with the opportunity to participate in ongoing scientific research. Existing either as stand-alone summer programs or as supplementary components to existing NSF research grants, the REU program focuses on introducing aspiring young scientists to the delights and complexities of science. Global Climate Change and Society (GCCS) is an intensive, 8-week REU program that began a 3-year run in the summer of 2001. Developed by a philosopher at the Colorado School of Mines, and a planetary scientist at Southwest Research Institute in Boulder, Colrado, GCCS is a unique experiment in research and pedagogy that introduces students to science by using a distinctive approach. Choosing as its topic the questions surrounding global climate change, the program explores the interwoven scientific, philosophical, and public policy issues that make the climate change debate such a volatile topic in contemporary society. Last summer, the program selected 12 undergraduates through a nationally advertised competition. Student interns came from diverse academic and cultural backgrounds and included physics, philosophy and public policy majors from elite liberal arts schools, major research institutions, and mainstream state universities. The program was held at the University of Colorado and the National Center for Atmospheric Research (NCAR), in Boulder, Colorado (Figure 1).