Gas-solid carbonation as a possible source of carbonates in cold planetary environments

International audienceCarbonates are abundant sedimentary minerals at the surface and sub-surface of the Earth and they have been proposed as tracers of liquid water in extraterrestrial environments. Their formation mechanism is since generally associated with aqueous alteration processes. Recently, carbonate minerals have been discovered on Mars' surface by different orbital or rover missions. In particular, the phoenix mission has measured from 1 to 5% of calcium carbonate (calcite type) within the soil (Smith P.H. et al., 2009). These occurrences have been reported in area were the relative humidity is significantly high (Boynton et al., 2009). The small concentration of carbonates suggests an alternative process on mineral grain surfaces (as suggested by Shaheen et al., 2010) than carbonation in aqueous conditions. Such an observation could rather point toward a possible formation mechanism by dust-gas reaction under current Martian conditions. To understand the mechanism of carbonate formation under conditions relevant to current Martian atmosphere and surface, we designed an experimental setup consisting of an infrared microscope coupled to a cryogenic reaction cell (IR-CryoCell setup). Three different mineral precursors of carbonates (Ca and Mg hydroxides, and a hydrated Ca silicate formed from Ca2SiO4), low temperature (from -10 to +30°C), and reduced CO2 pressure (from 100 to 2000 mbar) were utilized to investigate the mechanism of gas-solid carbonation at mineral surfaces. These mineral materials are crucial precursors to form Ca and Mg carbonates in humid environments (0 < relative humidity < 100%) at dust-CO2 or dust-water ice-CO2 interfaces. Our results reveal a significant and fast carbonation process for Ca hydroxide and hydrated Ca silicate. Conversely, only a moderate carbonation is observed for the Mg hydroxide. These results suggest that gas-solid carbonation process or carbonate formation at the dust-water ice-CO2 interfaces could be a currently active Mars' surface process. To the best of our knowledge, we report for the first time that calcium carbonate can be formed at a negative temperature (-10°C) via gas-solid carbonation of Ca hydroxide. We note that the carbonation process at low temperature (<0°C) described in the present study could also have important implications on the dust-water ice-CO2 interactions in cold terrestrial environments (e.g. Antarctic)

Passive Monitoring of HTTPS Service Use

International audienceHTTPS is used today to secure the majority of web communications and so enhance user privacy. Therefore, traffic monitoring techniques must evolve to remain useful, especially to support security considerations, as for example detecting and filtering the forbidden uses of a web service.However, privacy should be kept as intact as most as possible. This paper describes a new passive and transparent method to infer the use of a HTTPS service by extracting and interpreting only meaningful metadata derived from the encrypted traffic without deeply profile individual users. We propose a model using the sizes of objects loaded in the HTTPS service as a signature, by leveraging kernel density estimation, supportingthen a classification function. We assess this approach extensively on the Google Images Service but we show that our approach remains valid for other services. We succeed to achieve an accuracy of 99.18% when detecting particular keywords to be searched over a large dataset of 115,500 distinct keywords

Encrypted HTTP/2 Traffic Monitoring: Standing the Test of Time and Space

International audienceEncrypted HTTP/2 (h2) has been worldwide adopted since its official release in 2015. The major services over Internet use it to protect the user privacy against traffic interception. However, under the guise of privacy, one can hide the abnormal or even illegal use of a service. It has been demonstrated that machine learning algorithms combined with a proper set of features are still able to identify the incriminated traffic even when it is encrypted with h2. However, it can also be used to track normal service use and so endanger privacy of Internet users. Independently of the final objective, it is extremely important for a security practitioner to understand the efficiency of such a technique and its limit. No existing research has been achieved to assess how generic is it to be directly applicable to any service or website and how long an acceptable accuracy can be maintained. This paper addresses these challenges by defining an experimental methodology applied on more than 3000 different websites and also over four months continuously. The results highlight that an off-the-shelf machine-learning method to classify h2 traffic is applicable to many websites but a weekly training may be needed to keep the model accurate

Transparent and Service-Agnostic Monitoring of Encrypted Web Traffic

International audienceNowadays, most of Web services are accessed through HTTPS. While preserving user privacy is important, it is also mandatory to monitor and detect specific users' actions, for instance, according to a security policy. This paper presents a solution to monitor HTTP/2 traffic over TLS. It highly differs from HTTP/1.1 over TLS traffic what makes existing monitoring techniques obsolete. Our solution, H2Classifier, aims at detecting if a user performs an action that has been previously defined over a monitored Web service, but without using any decryption. It is thus only based on passive traffic analysis and relies on random forest classifier. A challenge is to extract representative values of the loaded content associated to a Web page, which is actually customized based on the user action. Extensive evaluations with five top used Web services demonstrate the viability of our technique with an accuracy between 94% and 99%

Temperature-dependent VNIR spectroscopy of hydrated Na-carbonates

The surfaces of the Galilean icy satellites Europa, Ganymede and Callisto, dominated by water ice, also show substantial amounts of non-water-ice compounds. These satellites will be the subject of close exploration by the ESA JUICE mission and the NASA Europa Multiple-Flyby Mission, which will focus on Ganymede and Europa, respectively. Among non-water-ice compounds thought to exist on the surfaces of the Jovian icy satellites, hydrated salt minerals have been proposed to exist as a by-product of endogenic processes. Safe detection of these minerals shall rely on laboratory spectroscopic analysis of these materials carried out under appropriate environmental conditions. Here we report on laboratory measurements, carried out in the framework of a Europlanet Transnational Access (TA) 2020 proposal approved in 2016, on two hydrated sodium carbonates, namely sodium carbonate monohydrate (Na2CO3·1H2O) and sodium carbonate decahydrate (Na2CO3·10H2O). Spectral profiles of these compounds were obtained in the visible and near-infrared (VNIR) spectral domain, taking advantage of the Cold Surfaces spectroscopy facility at the Institut de Planétologie et d'Astrophysique de Grenoble (IPAG), where such compounds can be measured under cryogenic conditions indicative of real planetary surfaces. Carbonates were first sieved so as to separate them in three different grain size ranges: 20-50 μm, 75-100 μm, and 125-150 μm. These grain sizes have been chosen to: (1) be indicative of typical regoliths known or expected to exist on the surface of the icy satellites, and (2) avoid overlapping between ranges, therefore minimizing particles contamination among the dimensional classes. Each grain size was then measured with the Spectro-Gonio-Radiometer facility in the overall 0.5-4.0 μm spectral range, with spectral sampling increasing with increasing wavelength. For each sample, the overall 93-279 K temperature ramp was acquired in 11 steps varying from 10 K to 25 K, imposed by time constraints. In particular, the uppermost temperature, 279 K, has been acquired both at the beginning and at end of the ramp, to check for any macroscopic physico-chemical changes in the sample. In sodium carbonate monohydrate, about ten spectral signatures are revealed in the spectral range 1.0-3.0 µm. These signatures are due in part to combinations and overtones of the fundamental vibration modes of the water molecule, and in part to the carbonate. For comparison, sodium carbonate decahydrate shows fewer diagnostic and generally wider signatures, due to the larger number of water molecules existing in this mineral. We analyzed the spectral behavior of the diagnostic signatures of these two hydrated minerals as a function of both grain size and temperature, deriving trends related to specific spectral parameters such as band center, band depth, band area, and bandwidth. We plan to complete this set of measurements with those obtained for anhydrous sodium carbonate, which serves as a valid comparison for the hydrated carbonates discussed here and may provide a valid support to spectroscopic analysis of bright faculae discovered by the NASA Dawn mission in crater Occator on the dwarf planet Ceres

Identification of Ammonium Salts on Comet 67P/C-G Surface from Infrared VIRTIS/Rosetta Data Based on Laboratory Experiments. Implications and Perspectives

The nucleus of comet 67P/Churyumov-Gerasimenko exhibits a broad spectral reflectance feature around 3.2 $\mu$m, which is omnipresent in all spectra of the surface, and whose attribution has remained elusive since its discovery. Based on laboratory experiments, we have shown that most of this absorption feature is due to ammonium (NH4+) salts mixed with the dark surface material. The depth of the band is compatible with semi-volatile ammonium salts being a major reservoir of nitrogen in the comet, which could dominate over refractory organic matter and volatile species. These salts may thus represent the long-sought reservoir of nitrogen in comets, possibly bringing their nitrogen-to-carbon ratio in agreement with the solar value. Moreover, the reflectance spectra of several asteroids are compatible with the presence of NH4+ salts at their surfaces. The presence of such salts, and other NH4+-bearing compounds on asteroids, comets, and possibly in proto-stellar environments, suggests that NH4+ may be a tracer of the incorporation and transformation of nitrogen in ices, minerals and organics, at different phases of the formation of the Solar System

MAORY for ELT: preliminary design overview

MAORY is one of the approved instruments for the European Extremely Large Telescope. It is an adaptive optics module, enabling high-angular resolution observations in the near infrared by real-time compensation of the wavefront distortions due to atmospheric turbulence and other disturbances such as wind action on the telescope. An overview of the instrument design is given in this paper