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تسجيل مستخدم جديدLISA: Mars and the limits of life
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We describe the results of the first tests made on LISA, a simulator of planetary environments designed and built in Padua, dedicated to the study of the limit of bacterial life on the planet Mars. Tests on the cryogenic circuit, on the UV illumination and on bacterial coltures at room temperature that shall be used as references are described.
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We present the biological results of some experiments performed in the Padua simulators of planetary environments, named LISA, used to study the limit of bacterial life on the planet Mars. The survival of Bacillus strains for some hours in Martian environment is shortly discussed.
We discuss the results of a remote sensing study that has revealed new details about an important rock unit dominated by two minerals that can be associated with volcanism (olivine) and life (carbonate). The study, which used a new analysis technique
on CRISM data, identified a region where no carbonates or clays are present, only large grain size olivine. This discovery shines new light on the formation and history of the olivine-carbonate rock within Jezero crater that will be explored by the Mars 2020 rover.
We present a cosmic perspective on the search for life and examine the likely number of Communicating Extra-Terrestrial Intelligent civilizations (CETI) in our Galaxy by utilizing the latest astrophysical information. Our calculation involves Galacti
c star-formation histories, metallicity distributions, and the likelihood of stars hosting Earth-like planets in Habitable Zones, under specific assumptions which we describe as the Astrobiological Copernican Weak and Strong conditions. These assumptions are based on the one situation in which intelligent, communicative life is known to exist - on our own planet. This type of life has developed in a metal-rich environment and has taken roughly 5 Gyr to do so. We investigate the possible number of CETI based on different scenarios. At one extreme is the Weak Astrobiological Copernican principle - such that a planet forms intelligent life sometime after 5 Gyr, but not earlier. The other is the Strong Condition in which life must form between 4.5 to 5.5 Gyr, as on Earth. In the Strong Condition (a strict set of assumptions), there should be at least 36$_{-32}^{+175}$ civilizations within our Galaxy: this is a lower limit, based on the assumption that the average life-time, L, of a communicating civilization is 100 years (based on our own at present). If spread uniformly throughout the Galaxy this would imply that the nearest CETI is at most 17000$_{-10000}^{+33600}$ light-years away, and most likely hosted by a low-mass M-dwarf star, far surpassing our ability to detect it for the foreseeable future. Furthermore, the likelihood that the host stars for this life are solar-type stars is extremely small and most would have to be M-dwarfs, which may not be stable enough to host life over long timescales. We furthermore explore other scenarios and explain the likely number of CETI there are within our Galaxy based on variations of our assumptions.
We extracted a Martian water-ice cloud climatology from OMEGA data covering 7 Martian years (MY 26-32). We derived two products, the Reversed Ice Cloud Index (ICIR) and the Percentage of Cloudy Pixels (PCP), indicating the mean cloud thickness and ne
bulosity over a regular grid (1{deg} longitude x 1{deg} latitude x 1{deg} Ls x 1 h Local Time). The ICIR has been shown to be a proxy of the water-ice column derived from the Mars Climate Database. The PCP confirms the location of the main cloud structures mapped with the ICIR, and gives a more accurate image of the cloud cover. We observed a denser cloud coverage over Hellas Planitia, Lunae Planum and over large volcanoes in the aphelion belt. For the first time, thanks to the fact that Mars Express is not in Sun-synchronous orbit, we can explore the cloud diurnal cycle at a given season by combining 7 years of observations. However, because of the eccentric orbit, the temporal coverage remains limited. Other limitations of the dataset are its small size, the difficult distinction between ice clouds and frosts, and the impact of surface albedo on data uncertainty. We could nevertheless study the diurnal cloud life cycle by averaging the data over larger regions: from specific topographic features (covering a few degrees in longitude and latitude) up to large climatic bands (all longitudes). We found that in the tropics around northern summer solstice, the diurnal thermal tide modulates the abundance of clouds, which is reduced around noon. At northern midlatitudes, clouds corresponding to the edge of the north polar hood are observed mainly in the morning and around noon during northern winter (Ls=260-30{deg}). Over Chryse Planitia, low lying morning fogs dissipate earlier and earlier in the afternoon during northern winter. Over Argyre, clouds are present over all daytime during two periods, around Ls = 30 and 160{deg}.
We have developed a torsion pendulum facility for LISA gravitational reference sensor ground testing that allows us to put significant upper limits on residual stray forces exerted by LISA-like position sensors on a representative test mass and to ch
aracterize specific sources of disturbances for LISA. We present here the details of the facility, the experimental procedures used to maximize its sensitivity, and the techniques used to characterize the pendulum itself that allowed us to reach a torque sensitivity below 20 fNm /sqrt{Hz} from 0.3 to 10 mHz. We also discuss the implications of the obtained results for LISA.
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