Ammonium salts on comet 67P: The distribution of carbon and nitrogen in the Solar System is thought to reflect the stability of carbon- and nitrogen-bearing molecules when exposed to the heat of the forming Sun. Comets have a low nitrogen-to-carbon ratio, which is contrary to expectations because they originate in the outer Solar System where nitrogen species should be common. Poch et al. used laboratory experiments to simulate cometary surfaces and compared the resulting spectra with comet 67P/Churyumov-Gerasimenko. They assigned a previously unidentified infrared absorption band to nitrogen-containing ammonium salts. The salts could contain enough nitrogen to bring the comet's nitrogen-to-carbon ratio in line with the Sun's. Science , this issue p. eaaw7462

The study of the fluvial systems present on the Martian surface is a key in the investigation of the paleoclimate of the planet: Various indications suggest that these features could have formed under climatic conditions very different from the present one. For this reason, it seems necessary to update the previous maps of Martian valleys using newer mosaics and data at higher resolution. In this work we present a detailed global map of Martian valleys classified according to their morphology. Our data set includes all the valleys longer than 20 km mapped within the QGIS (Quantum Geographic Information System) software. With respect to previous global maps, the coupling of topographic information with data of higher image quality allowed us a better mapping of these structures at a fine scale: New small valleys and more tributaries for several systems have been observed. We mapped valleys of various typologies for a global total length of 773,559 km. The mapped valley networks cover the 69% of this total length. Moreover, a rough estimation of the valleys' age spatial distribution was performed. We found that the 94% of the mapped valleys have a maximum age consistent with an origin in the Noachian period; the 4% have a Hesperian maximum age, while the remaining 2% have a maximum age consistent with an origin in the Amazonian period. Finally, we also estimated the total eroded volume of the mapped valley networks finding a value in the order of 3 × 10¹⁴ m³in good agreement with what found in literature.

In this work, we study the kinetics of thermal decomposition of MgCO₃ in the form of particles of known size. In the experiments, the material is heated to a known temperature in a vacuum oven, and it is characterized, both before and after heating, by infrared spectroscopy and gravimetry. The agreement between the results of the two techniques is excellent. These results are rationalized by means of a model based on Languir’s law, and the comparison with the experiments allows us to estimate the activation energy of the process. The reabsorption of atmospheric water by the oxide is shown spectroscopically, finding that is strongly influenced by the temperature of the process.

In this paper, the thermal decomposition kinetics of a class of minerals that we call White Soft Minerals (WSMs) is studied by means of theoretical and experimental methods, in connection to the transport of extraterrestrial organic matter to Earth and the possible use of the decomposition reaction in the characterization of these minerals in space. WSMs include, under a single denomination, carbonates and sulphates of Mg, Fe, and Ca. To improve the present knowledge of the properties of such materials, we use the following techniques: kinetic models for chemical decomposition, atmospheric entry models, spectroscopy, and gravimetric analyses. Model results show that the atmospheric entry of WSM grains is strongly affected by their thermal decomposition. The decomposition reaction, being strongly endothermic, tends to significantly lower the grain temperature during the atmospheric entry, especially at high altitudes and for grazing entries. A previously proposed infrared spectroscopic technique to evaluate the degree of advancement of the reaction is found to be in good agreement with gravimetric measurements for calcium carbonate. The numerical model developed for the atmospheric entry scenarios is used to interpret experimental results. These main findings show that an additional contribution to the reaction enthalpy is needed to reproduce the experimental results, suggesting that the present theoretical model needs improvements such as the account of gas diffusion in the materials.