Soil carbon distribution and site characteristics in hyper-arid soils of the Atacama Desert: A site with Mars-like soils

The soil carbon content and its relation to site characteristics are important in evaluating current local, regional, and global soil C storage and projecting future variations in response to climate change. In this study we analyzed the concentration of organic and inorganic carbon and their relationship with in situ climatic and geological characteristics in 485 samples of surface soil and 17 pits from the hyper-arid area and 51 samples with 2 pits from the arid–semiarid region from the Atacama Desert located in Peru and Chile. The soil organic carbon (SOC) in hyperarid soils ranged from 1.8 to 50.9 μg C per g of soil for the 0–0.1 m profile and from 1.8 to 125.2 μg C per g of soil for the 0–1 m profile. The analysis of climatic (temperature and precipitation), elevation, and some geologic characteristics (landforms) associated with hyper-arid soils explained partially the SOC variability. On the other hand, soil inorganic carbon (SIC) contents, in the form of carbonates, ranged from 200 to 1500 μg C per g of soil for the 0–0.1 m profile and from 200 to 3000 μg C per g of soil for the 0–1.0 m profile in the driest area. The largest accumulations of organic and inorganic carbon were found near to arid–semiarid areas. In addition, the elemental carbon concentrations show that the presence of other forms of inorganic carbon (e.g. graphite, etc.) was negligible in these hyperarid soils. Overall, the top 1 m soil layer of hyperarid lands contains ∼11.6 Tg of organic carbon and 344.6 Tg of carbonate carbon. The total stored carbon was 30.8-fold the organic carbon alone. To our knowledge, this is the first study evaluating the total budget carbon on the surface and shallow subsurface on ∼160,000 km² of hyperarid soils.     

Did life exist on Mars? Search for organic and inorganic signatures, one of the goals for “SAM” (sample analysis at Mars)

Observation of Mars shows signs of a past Earth-like climate, and, in that case, there is no objection to the possible development of life, in the underground or at the surface, as in the terrestrial primitive biosphere. Sample analysis at Mars (SAM) is an experiment which may be proposed for atmospheric, ground and underground in situ measurements. One of its goals is to bring direct or indirect information on the possibility for life to have developed on Mars, and to detect traces of past or present biological activity. With this aim, it focuses on the detection of organic molecules: volatile organics are extracted from the sample by simple heating, whereas refractory molecules are made analyzable (i.e. volatile), using derivatization technique or fragmentation by pyrolysis. Gaseous mixtures thus obtained are analyzed by gas chromatography associated to mass spectrometry. Beyond organics, carbonates and other salts are associated to the dense and moist atmosphere necessary to the development of life, and might have formed and accumulated in some places on Mars. They represent another target for SAM. Heating of the samples allows the analysis of structural gases of these minerals (CO₂ from carbonates, etc.), enabling to identify them. We also show, in this paper, that it may be possible to discriminate between abiotic minerals, and minerals (shells, etc.) created by living organisms.     

From Titan’s tholins to Titan’s aerosols: Isotopic study and chemical evolution at Titan’s surface

In the present work, we focused on the possible isotopic fractionation of carbon during the processes involved in the formation of Titan’s tholins. We present the first results obtained on the ¹²C/¹³C isotopic ratios measured on Titan’s tholins synthesized in laboratory with cold plasma discharges. Measurements of isotopic ratio ¹²C/¹³C, done both on tholins and on the initial gas mixture (N₂:CH₄ (98:2)) used to produce them, do not show any evident deficit or enrichment in ¹³C relatively to ¹²C in the synthesized tholins, compared to the initial gas mixture. This observation allows to go further in the analyses of the ACP experiment data, including part of the Cassini–Huygens mission.     

Genesis and preservation of a uranium-rich paleozoic epithermal system with a surface expression (Northern Flinders Ranges, South Australia): radiogenic heat driving regional hydrothermal circulation over geological timescales

The surface expressions of hydrothermal systems are prime targets for astrobiological exploration, and fossil systems on Earth provide an analogue to guide this endeavor. The Paleozoic Mt. Gee-Mt. Painter system (MGPS) in the Northern Flinders Ranges of South Australia is exceptionally well preserved and displays both a subsurface quartz sinter (boiling horizon) and remnants of aerial sinter pools that lie in near-original position. The energy source for the MGPS is not related to volcanism but to radiogenic heat produced by U-Th-K-rich host rocks. This radiogenic heat source drove hydrothermal circulation over a long period of time (hundreds of millions of years, from Permian to present), with peaks in hydrothermal activity during periods of uplift and high water supply. This process is reflected by ongoing hot spring activity along a nearby fault. The exceptional preservation of the MGPS resulted from the lack of proximal volcanism, coupled with tectonics driven by an oscillating far-field stress that resulted in episodic basement uplift. Hydrothermal activity caused the remobilization of U and rare earth elements (REE) in host rocks into (sub)economic concentrations. Radiogenic-heat-driven systems are attractive analogues for environments that can sustain life over geological times; the MGPS preserves evidence of episodic fluid flow for the past ～300 million years. During periods of reduced hydrothermal activity (e.g., limited water supply, quiet tectonics), radiolytic H(2) production has the potential to support an ecosystem indefinitely. Remote exploration for deposits similar to those at the MGPS systems can be achieved by combining hyperspectral and gamma-ray spectroscopy.     

Determination of surface global radiation using METEOSAT images and ground based visibility measurements

Our purpose is the forecast of the global radiation. As a first step we try to determine the global radiation as function of other predictable parameters. First the daily average values of the relative global radiation was considered as parabolic function of the cloud coverage obtained from METEOSAT images, an empirical formula was determined for calculation of the relative global radiation from the cloud amount. The correct this formula the cloud coverage and ground based visibility data were used. The value of the multiple correlation coefficient presenting the accuracy of the new formula was 0.96 for Budapest, and 0.93 for region of Hungary. This fact indicates that we have a sufficiently correct formula for calculation of the global radiation.     

Implications of Rotation, Orbital States, Energy Sources, and Heat Transport for Internal Processes in Icy Satellites

Internal processes in icy satellites, e.g. the exchange of material from the subsurface to the surface or processes leading to volcanism and resurfacing events, are a consequence of the amount of energy available in the satellites’ interiors. The latter is mainly determined shortly after accretion by the amount of radioactive isotopes incorporated in the silicates during the accretion process. However, for satellites—as opposed to single objects—important contributions to the energy budget on long time-scales can come from the interaction with other satellites (forcing of eccentricities of satellites in resonance) and consequently from the tidal interaction with the primary planet. Tidal evolution involves both changes of the rotation state—usually leading to the 1:1 spin orbit coupling—and long-term variations of the satellite orbits. Both processes are dissipative and thus connected with heat production in the interior. The way heat is transported from the interior to the surface (convection, conduction, (cryo-) volcanism) is a second main aspect that determines how internal processes in satellites work. In this chapter we will discuss the physics of heat production and heat transport as well as the rotational and orbital states of satellites. The relevance of the different heat sources for the moons in the outer solar system are compared and discussed.     

Derniers resultats de calcul d'orbite SPOT et TOPEX/POSEIDON obtenus avec DORIS

DORIS is a tracking system developed by CNES to support precise orbit computation of the US-French TOPEX/POSEIDON project. Moreover DORIS data are currently processed to compute SPOT2 and SPOT3 orbits. Although the SPOT satellites are at 800 km altitudes, their orbits reach the decimetric level, to be compared to the 3–4 cm RMS on the T/P radial component.For each type of orbit, there is an adaptive period of a few months which is used for improving the precision. The paper describes what has been done to reduce some items in the total error budget. The latest results will be presented as well as the criteria which are settled to characterize the improvements.Finally, the future developments of DORIS and the potential projects flowing DORIS will be outlined such as ENVISAT and TOPEX/POSEIDON Follow On.     

Plasma Motion and Kinematics in Cool and Hot Stars

The environments of both hot and cool stars are the sites of highly dynamic processes involving motion of gas and plasma in winds, flows across shocks, plasma motions in closed magnetic fields, or streams along magnetospheric accretion funnels. X-ray spectroscopy has opened new windows toward the study of these processes. Kinematics are evident in line shifts and line broadening, and also more indirectly through the analysis and interpretation of density-sensitive lines. In hot stellar winds, expanding-wind kinematics are directly seen in broadened lines although the broadening has turned out to often be smaller than anticipated, and some lines are so narrow that coronal models have been revived. Although X-ray spectra of cool stars have shown line shifts and broadening due to the kinematics of the entire corona, e.g., in binary systems, intrinsic mass motions are challenging to observe at the presently available resolution. Much indirect evidence for mass motion in magnetic coronae is nevertheless available. And finally, spectral diagnostics has also led to a new picture of X-ray production in accreting pre-main sequence stars where massive accretion flows collide with the photospheric gas, producing shocks in which gas is heated to high temperatures. We summarize evidence for the above mechanisms based on spectroscopic data from XMM-Newton and Chandra.     

A novel SETI strategy targeting the solar focal regions of the most nearby stars

Many hypotheses have been raised to explain the famous Fermi paradox. One of them is that self-replicating probes could have explored the whole Galaxy, including our Solar System, and that they are still to be detected. In this scenario, it is proposed here that probes from neighboring stellar systems could use the stars they orbit as gravitational lenses to communicate efficiently with each other. Under this hypothesis, a novel SETI approach would be to monitor the solar focal regions of the most nearby stars to search for communication devices. The envisioned devices are probably not detectable by imagery or stellar occultation, but an intensive multi-spectral monitoring campaign could possibly detect some communication leakages. Another and more direct option would be to message the focal regions of nearby stars in an attempt to initiate a reaction.