Testing Earth-like atmospheric evolution on exo-Earths through oxygen absorption: required sample sizes and the advantage of age-based target selection

Life has had a dramatic impact on the composition of Earth's atmosphere over time, which suggests that statistical studies of other inhabited planets' atmospheres could reveal how they co-evolve with life. While many evolutionary pathways are possible for inhabited worlds, a possible starting hypothesis is that most of them evolve similarly to Earth, which we propose could lead to a positive "age-oxygen correlation" between the ages of inhabited planets and the fraction which have oxygen-rich atmospheres. We demonstrate that next-generation space observatories currently under consideration could test this hypothesis, but only if the stellar age distribution of the target sample is carefully considered. We explore three possible parameterizations of the age-oxygen correlation, finding that they yield similar results. Finally, we examine how abiotic oxygen sources could affect the results, and discuss how measuring the age-dependence of oxygen could shed light on whether it is a reliable biosignature. Future efforts can expand upon this groundwork by incorporating detailed models of the redox balance of terrestrial planets and its dependence on stellar and planetary properties.Comment: 13 pages, 3 figures, accepted to Ap

"You Paint Me a Ship as is Like a Ship": The Verkin Ship Portraits

Commercial maritime photography archives are rich, largely underutilized, resources and examining photographs from them within the context of the history of ship portraiture offers another way of understanding these collections. Images from the Verkin Studio archive from Galveston, Texas, because of their subject matter and adherence to specific representational conventions, maybe viewed as a step in the evolution of ship portraiture. Ship portraits appealed to owners, captains, officers, and crew members alike, and from the eighteenth century onward, a diverse clientele was supplied by craftsmen of varying skill. By the twentieth century, the creation of these pictures using a camera — while maintaining the visual conventions and centuries-old practices of manufacture and sale — testifies to continuity in the craft of ship portraiture. Photography, the quick and relatively inexpensive way to obtain representations from life, supplants the quick and inexpensive pierhead painter. Résumé Les archives photographiques de la marine marchande constituent une réserve fabuleuse, mais fort peu exploitée, et l'examen des clichés qu'elles renferment dans le contexte historique des reproductions artistiques de navires jette une lumière nouvelle sur les collections de ce genre. On peut considérer les images tirées des archives du studio Verkin, à Galveston (Texas), comme une étape dans l'évolution des reproductions artistiques de navires, en raison de leur thème et de leur respect de normes de représentation très précises. Les portraits de navires plaisaient aux affréteurs, aux capitaines, aux officiers et aux membres d'équipages. Dès le xviif siècle, des artistes au talent variable s'efforcèrent de satisfaire une clientèle diversifiée. Au XXe siècle, la création de telles images par le truchement d'un appareil photo - sans déroger aux conventions visuelles ni aux pratiques séculaires de la fabrication et de la vente -démontre la continuité de l'art de la reproduction artistique des navires. La photographie, méthode rapide et relativement peu coûteuse de représenter la réalité, supplantera donc rapidement l'artiste-peintre, qui exécutait un tableau en deux temps trois mouvements pour quelques sous sur les quais

Prospects for the characterization of habitable planets

With thousands of exoplanets now identified, the characterization of habitable planets and the potential identification of inhabited ones is a major challenge for the coming decades. We review the current working definition of habitable planets, the upcoming observational prospects for their characterization and present an innovative approach to assess habitability and inhabitation. This integrated method couples for the first time the atmosphere and the interior modeling with the biological activity based on ecosystem modeling. We review here the first applications of the method to asses the likelihood and impact of methanogenesis for Enceladus, primitive Earth, and primitive Mars. Informed by these applications for solar system situations where habitability and inhabitation is questionned, we show how the method can be used to inform the design of future space observatories by considering habitability and inhabitation of Earth-like exoplanets around sun-like stars.Comment: 16 pages, 4 figure

A Thousand Earths: A Very Large Aperture, Ultralight Space Telescope Array for Atmospheric Biosignature Surveys

An outstanding, multidisciplinary goal of modern science is the study of the diversity of potentially Earth-like planets and the search for life in them. This goal requires a bold new generation of space telescopes, but even the most ambitious designs yet hope to characterize several dozen potentially habitable planets. Such a sample may be too small to truly understand the complexity of exo-earths. We describe here a notional concept for a novel space observatory designed to characterize 1000 transiting exo-earth candidates. The Nautilus concept is based on an array of inflatable spacecraft carrying very large diameter (8.5 m), very low weight, multiorder diffractive optical elements (MODE lenses) as light-collecting elements. The mirrors typical to current space telescopes are replaced by MODE lenses with a 10 times lighter areal density that are 100 times less sensitive to misalignments, enabling lightweight structure. MODE lenses can be cost-effectively replicated through molding. The Nautilus mission concept has a potential to greatly reduce fabrication and launch costs and mission risks compared to the current space telescope paradigm through replicated components and identical, lightweight unit telescopes. Nautilus is designed to survey transiting exo-earths for biosignatures up to a distance of 300 pc, enabling a rigorous statistical exploration of the frequency and properties of life-bearing planets and the diversity of exo-earths.Gordon and Betty Moore Foundation; NASA's Science Mission DirectorateThis 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]

Sztereo algoritmus légköri felhők rekonstrukciójához = Stereo Algorithm for Atmospheric Cloud Reconstruction

Ebben a cikkben bemutatunk egy légköri felhők felületét rekonstruáló eljárást, ami sztereó kamerarendszer képeit használja fel. Bemutatásra kerül az egész folyamat a javasolt kamerarendszertől a 3D ponthalmaz előállításáig, de a fő hangsúly a felhőszegmentáláson és a sztereó rekonstrukció képfeldolgozási lépésein lesz

Location of the Polyamine Binding Site in the Vestibule of the Nicotinic Acetylcholine Receptor Ion Channel

To map the structure of a ligand-gated ion channel, we used the photolabile polyamine-containing toxin MR44 as photoaffinity label. MR44 binds with high affinity to the nicotinic acetylcholine receptor in its closed channel conformation. The binding stoichiometry was two molecules of MR44 per receptor monomer. Upon UV irradiation of the receptor-ligand complex, (125)I-MR44 was incorporated into the receptor alpha-subunit. From proteolytic mapping studies, we conclude that the site of (125)I-MR44 cross-linking is contained in the sequence alpha His-186 to alpha Leu-199, which is part of the extracellular domain of the receptor. This sequence partially overlaps in its C-terminal region with one of the three loops that form the agonist-binding site. The agonist carbachol and the competitive antagonist alpha-bungarotoxin had only minor influence on the photocross-linking of (125)I-MR44. The site where the hydrophobic head group of (125)I-MR44 binds must therefore be located outside the zone that is sterically influenced by agonist bound at the nicotinic acetylcholine receptor. In binding and photocross-linking experiments, the luminal noncompetitive inhibitors ethidium and triphenylmethylphosphonium were found to compete with (125)I-MR44. We conclude that the polyamine moiety of (125)I-MR44 interacts with the high affinity noncompetitive inhibitor site deep in the channel of the nicotinic acetylcholine receptor, while the aromatic ring of this compound binds in the upper part of the ion channel (i.e. in the vestibule) to a hydrophobic region on the alpha-subunit that is located in close proximity to the agonist binding site. The region of the alpha-subunit labeled by (125)I-MR44 should therefore be accessible from the luminal side of the vestibule

VE-PTP maintains the endothelial barrier via plakoglobin and becomes dissociated from VE-cadherin by leukocytes and by VEGF

We have shown recently that vascular endothelial protein tyrosine phosphatase (VE-PTP), an endothelial-specific membrane protein, associates with vascular endothelial (VE)–cadherin and enhances VE-cadherin function in transfected cells (Nawroth, R., G. Poell, A. Ranft, U. Samulowitz, G. Fachinger, M. Golding, D.T. Shima, U. Deutsch, and D. Vestweber. 2002. EMBO J. 21:4885–4895). We show that VE-PTP is indeed required for endothelial cell contact integrity, because down-regulation of its expression enhanced endothelial cell permeability, augmented leukocyte transmigration, and inhibited VE-cadherin–mediated adhesion. Binding of neutrophils as well as lymphocytes to endothelial cells triggered rapid (5 min) dissociation of VE-PTP from VE-cadherin. This dissociation was only seen with tumor necrosis factor α–activated, but not resting, endothelial cells. Besides leukocytes, vascular endothelial growth factor also rapidly dissociated VE-PTP from VE-cadherin, indicative of a more general role of VE-PTP in the regulation of endothelial cell contacts. Dissociation of VE-PTP and VE-cadherin in endothelial cells was accompanied by tyrosine phoshorylation of VE-cadherin, β-catenin, and plakoglobin. Surprisingly, only plakoglobin but not β-catenin was necessary for VE-PTP to support VE-cadherin adhesion in endothelial cells. In addition, inhibiting the expression of VE-PTP preferentially increased tyrosine phosphorylation of plakoglobin but not β-catenin. In conclusion, leukocytes interacting with endothelial cells rapidly dissociate VE-PTP from VE-cadherin, weakening endothelial cell contacts via a mechanism that requires plakoglobin but not β-catenin

Blood flow controls bone vascular function and osteogenesis

While blood vessels play important roles in bone homeostasis and repair, fundamental aspects of vascular function in the skeletal system remain poorly understood. Here we show that the long bone vasculature generates a peculiar flow pattern, which is important for proper angiogenesis. Intravital imaging reveals that vessel growth in murine long bone involves the extension and anastomotic fusion of endothelial buds. Impaired blood flow leads to defective angiogenesis and osteogenesis, and downregulation of Notch signalling in endothelial cells. In aged mice, skeletal blood flow and endothelial Notch activity are also reduced leading to decreased angiogenesis and osteogenesis, which is reverted by genetic reactivation of Notch. Blood flow and angiogenesis in aged mice are also enhanced on administration of bisphosphonate, a class of drugs frequently used for the treatment of osteoporosis. We propose that blood flow and endothelial Notch signalling are key factors controlling ageing processes in the skeletal system