316 research outputs found

    Impact and Signatures of Deglaciation on the Cryosphere, Landscape, and Habitability of Earth and Mars

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    Science questions can help bridge Astrobiology and Earth Science disciples around the theme of planetary deglaciation

    Planetary Trojans - the main source of short period comets?

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    We present a short review of the impact regime experienced by the terrestrial planets within our own Solar system, describing the three populations of potentially hazardous objects which move on orbits that take them through the inner Solar system. Of these populations, the origins of two (the Near-Earth Asteroids and the Long-Period Comets) are well understood, with members originating in the Asteroid belt and Oort cloud, respectively. By contrast, the source of the third population, the Short-Period Comets, is still under debate. The proximate source of these objects is the Centaurs, a population of dynamically unstable objects that pass perihelion between the orbits of Jupiter and Neptune. However, a variety of different origins have been suggested for the Centaur population. Here, we present evidence that at least a significant fraction of the Centaur population can be sourced from the planetary Trojan clouds, stable reservoirs of objects moving in 1:1 mean-motion resonance with the giant planets (primarily Jupiter and Neptune). Focusing on simulations of the Neptunian Trojan population, we show that an ongoing flux of objects should be leaving that region to move on orbits within the Centaur population. With conservative estimates of the flux from the Neptunian Trojan clouds, we show that their contribution to that population could be of order ~3%, while more realistic estimates suggest that the Neptune Trojans could even be the main source of fresh Centaurs. We suggest that further observational work is needed to constrain the contribution made by the Neptune Trojans to the ongoing flux of material to the inner Solar system, and believe that future studies of the habitability of exoplanetary systems should take care not to neglect the contribution of resonant objects (such as planetary Trojans) to the impact flux that could be experienced by potentially habitable worlds.Comment: 16 pages, 4 figures, published in the International Journal of Astrobiology (the arXiv.org's abstract was shortened, but the original one can be found in the manuscript file

    Thresholds of Detection and Identification of Halite Nodule Habitats in the Atacama Desert Using Remote Imaging

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    The guiding theme of Mars exploration is shifting from global and regional habitability assessment to biosignature detection. To locate features likely to contain biosignatures, it is useful to focus on the reliable identification of specific habitats with high biosignature preservation potential. Proposed chloride deposits on Mars may represent evaporitic environments conducive to the preservation of biosignatures. Analogous chloride- bearing, salt-encrusted playas (salars) are a habitat for life in the driest parts of the Atacama Desert, and are also environments with a taphonomic window. The specific geologic features that harbor and preserve microorganisms in Atacama salars are sub- meter to meter scale salt protuberances, or halite nodules. This study focuses on the ability to recognize and map halite nodules using images acquired from an unmanned aerial vehicle (UAV) at spatial resolutions ranging from mm/pixel to that of the highest resolution orbital images available for Mars

    Evolution of IGF-1 in children born small for gestational age and with growth retardation, treated by growth hormone adapted to IGF-1 levels after 1 year

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    AIM: This study was designed to estimate the percentage of growth hormone (GH)-treated children born small for gestational age (SGA), with serum IGF-1 >2 SDS before and after GH dose adaptation. METHODS: SGA boys aged 4-9 and girls aged 4-7 with a height <-2 SDS and an annual growth rate below the mean received a subcutaneous GH dose of 57 mug/kg/day for 2 years. The GH dose was to be decreased by 30% in children with serum IGF-1 >2 SDS at 12 months and on the previous sample. The GH dose could be reduced a second time to 35 mug/kg.day. IGF-1 and IGFBP-3 dosages were centralized. RESULTS: Among the 49 (21 boys) children included in the study, 8 (16.3%) had an IGF-1 >2 SDS consecutively at 9 and 12 months (95% CI 7.3, 29.7). The GH dose was decreased in 6/8 children. However, IGF-1 levels were elevated at several nonconsecutive determinations in 45% (95% CI 28.4, 56.6) of the patients. CONCLUSION: A high IGF-1 level is observed in 45% of the GH SGA-treated children with a relatively high dose of GH. A 30% reduction in the GH dose causes a decrease in IGF-1 below 2 SDS in most children

    Relation of gallbladder function and Helicobacter pylori infection to gastric mucosa inflammation in patients with symptomatic cholecystolithiasis

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    Background. Inflammatory alterations of the gastric mucosa are commonly caused by Helicobacter pylori (Hp) infection in patients with symptomatic gallstone disease. However, the additional pathogenetic role of an impaired gallbladder function leading to an increased alkaline duodenogastric reflux is controversially discussed. Aim:To investigate the relation of gallbladder function and Hp infection to gastric mucosa inflammation in patients with symptomatic gallstones prior to cholecystectomy. Patients: Seventy-three patients with symptomatic gallstones were studied by endoscopy and Hp testing. Methods: Gastritis classification was performed according to the updated Sydney System and gallbladder function was determined by total lipid concentration of gallbladder bile collected during mainly laparoscopic cholecystectomy. Results: Fifteen patients revealed no, 39 patients mild, and 19 moderate to marked gastritis. No significant differences for bile salts, phospholipids, cholesterol, or total lipids in gallbladder bile were found between these three groups of patients. However, while only 1 out of 54 (< 2%) patients with mild or no gastritis was found histologically positive for Hp, this infection could be detected in 14 (74%) out of 19 patients with moderate to marked gastritis. Conclusion: Moderate to marked gastric mucosa inflammation in gallstone patients is mainly caused by Hp infection, whereas gallbladder function is not related to the degree of gastritis. Thus, an increased alkaline duodenogastric reflux in gallstone patients seems to be of limited pathophysiological relevance. Copyright (c) 2006 S. Karger AG, Basel
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