Mercure (planète)

Résumé

Mercure est la planète la plus proche du Soleil et la moins massive du Système solaire. Son éloignement au Soleil est compris entre (soit 46 et de kilomètres), ce qui correspond à une excentricité orbitale de 0,2 . Elle est visible à l'œil nu depuis la Terre avec un diamètre apparent de , et une magnitude apparente de ; son observation est toutefois rendue difficile par son élongation toujours inférieure à 28,3° qui la noie le plus souvent dans l'éclat du soleil. En pratique, cette proximité avec le soleil implique qu'elle ne peut être vue que près de l'horizon occidental après le coucher du soleil ou près de l'horizon oriental avant le lever du soleil, en général au crépuscule. Mercure a la particularité d'être en résonance spin-orbite 3:2, sa période de révolution (~) valant exactement sa période de rotation (~), et donc la moitié d'un jour solaire (~). Ainsi, relativement aux étoiles fixes, elle tourne sur son axe exactement trois fois toutes les deux révolutions autour du Solei

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https://fr.wikipedia.org/wiki/Mercure_(plan%C3%A8te)

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Prenatal exposure to mercury causes neurodevelopmental disorders and neurological pathologies in infants, such as microcephaly and mental retardation. Despite critical importance, the molecular interactions leading to mercury toxicity are yet to be elucidated. We first used a cell-free assay to investigate mercury effects on purified γ-secretase activity. Next, we treated adult Drosophila melanogaster with mercury and collected control and mercury-treated embryos, which were subjected to mild hypotonic protein extraction, or immunostained to reveal nervous system morphology. Embryos left to develop into adults were examined for wing phenotypes. Relative to control metals, we found that mercury strongly inhibits in vitro γ-secretase processing of both amyloid-β precursor protein (APP) and Notch. Mercury inhibited APP and Notch cleavage in a dose-dependent manner, with IC(50) values of 50-125 nM, and is therefore comparable in potency to benchmark γ-secretase inhibitors. Immunoblot analysis of embryonic protein extracts showed that mercury inhibits Notch cleavage by γ-secretase in vivo. This is accompanied by severe neurodevelopmental abnormalities in embryos and adult wing-notching phenotypes. Our findings provide first evidence that mercury is a direct and potent γ-secretase inhibitor and suggest that inhibition of γ-secretase and disruption of the Notch developmental pathway potentially contribute to mercury-induced toxicity in the nervous system.

2011

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As part of a long-term project to determine abundances and astrophysical properties of evolved red stars in open clusters, we present high-precision DDO photoelectric observations for a sample of 33 red giant candidates projected in the fields of nine Galactic open clusters. These data are supplemented with UBV photoelectric photometry of 24 of these stars as well as with CORAVEL radial-velocity observations for 13 red giant candidates in four of the clusters. We also present Washington photoelectric photometry of a small sample of red giant candidates of the open cluster Ruprecht 97. The likelihood of cluster membership for each star photometrically observed and for 23 additional red giant candidates with UBV and DDO data available in the literature, is evaluated by using two independent photometric criteria. Nearly 82% of the analysed stars are found to have a high probability of being cluster giants. Photometric membership probabilities show very good agreement with those obtained from CORAVEL radial velocities. While E(B - V) colour excesses were determined from combined B - V and DDO colours, calibrations of the DDO system were used to derive MK spectral types, effective temperatures and metallicities.The derived DDO metallicities range between values typical of moderately metal-poor clusters ([Fe/H] = -0.19) to moderately metal-rich ([Fe/H] = 0.25) ones. (c) 2009 WILEY-VCH Verla, GmbH&Co. KGaA, Weinheim.

2008

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An innovative photogrammetric pipeline has been developed by INAF-Padova for the processing of the stereo images from the CaSSIS (Colour and Stereo Imaging System) (Thomas et al., 2014). CaSSIS is the multispectral stereo push frame camera on board ExoMars TGO (Trace Gas Orbiter) which will image 1.5% of the Mars surface in stereo mode with a spatial resolution of 4.6 m/pixel: the highest resolution single pass stereo capability currently operating a Mars. Data acquisition started in April 2018. The camera is able to provide two images of the same target from two different points of view along the same orbit and within one minute. The telescope is mounted on a rotational stage and its boresight is oriented to 10 degrees with respect to nadir direction. After the acquisition of the first set of images looking forward along track, the rotational stage is rotated by 180 degrees and a second set of images (looking backward) is acquired. The stereo pairs can then be processed to provide the 3D topography of specific targets. The suite of photogrammetry and imaging tools, named 3DPD (3Dimensional reconstruction of Planetary Data) (Simioni a al. 2017), is designed for processing stereo push frame data and producing the three-dimensional data for geomorphological analysis of planetary surfaces. The workflow involves a MATLAB tool for the preparation of the inputs (the mosaicked images and the projection matrices) to be ingested into the 3DPD matching core software. The pipeline is in continuous development and routinely ingests a large number of images that CaSSIS is presently acquiring and will continue to acquire in the future. CaSSIS 3DPD products are the unique DTMs available nowadays and the stereo products have been considered in some scientific work (as described in Section 6.2). The same pipeline faces the need of a dedicated pipeline for the Mercury Global Mapping with the Spectrometers and Imagers for the Mercury Planetary Orbiter (MPO) BepiColombo Integrated Observatory SYStem (SIMBIO-SYS) (Cremonese et al., 2020).

PERGAMON-ELSEVIER SCIENCE LTD2021

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PERGAMON-ELSEVIER SCIENCE LTD2021