Evaluation of CaSO₄micrograins in the context of organic matter delivery: thermochemistry and atmospheric entry

Abstract

In this paper, anhydrous calcium sulphate CaSO4 (anhydrite) is considered as a carrier material for organic matter delivery from Space to Earth. Its capability of incorporating important fractions of water, leading to different species like bassanite and gypsum, as well as organic molecules; its discovery on Mars surface and in meteorites; the capability to dissipate much energy by its chemical decomposition into solid (CaO) and gaseous (SO3) oxide, make anhydrite a very promising material in an astrobiological perspective. Since chemical cooling has been recently considered by some of the present authors for the case of Ca/Mg carbonates, CaSO4 can be placed into a class of ‘white soft minerals’ (WSM) of astrobiological interest. In this context, CaSO4 is evaluated here by using the atmospheric entry model previously developed for carbonates. The model includes grain dynamics, thermochemistry, stoichiometry, radiation and evaporation heat losses. Results are discussed in comparison with MgCO3 and CaCO3 and show that sub-mm anhydrite grains are potentially effective organic matter carriers. A Monte Carlo simulation is used to provide distributions of the sulphate fraction as a function of altitude. Two-zone model results are presented to support the isothermal grain hypothesis.

Kinetics of White Soft Minerals (WSMs) Decomposition under Conditions of Interest for Astrobiology: A Theoretical and Experimental Study

“…These numbers are very close to the average densities of the mineral and the corresponding oxide, in all cases of study. The isothermal hypothesis is supported by the Biot number analysis: considering the temperatures and the grain radii involved in our case studies, the Biot number is much smaller than one (∼10 −4 ), so the body temperature can be considered uniform [35,36].…”

“…When CO 2 is completely evaporated and the grain becomes pure oxide, the grain mass does not change anymore and the temperature increases dramatically, only mitigated by blackbody radiation [34,35]. On the other hand, a sulphate micrograin can survive the atmospheric entry with a partial decomposition [36].…”

“…In order to evaluate the thermal behavior of sub-mm grains during the atmospheric entry process, it is necessary to develop numerical models of this process as those built in the past in the case of silicates [33]. The first actual atmospheric entry scenarios for carbonate and sulphate grains have been published by some of the present authors [34][35][36]. The entry model was realized to provide evidence that carbonate and sulphate decomposition might act as possible cooling mechanism, in the delivery of organic matter from space to Earth [37].…”

Computer simulations of biotic chiral selection scenarios

“…Most of the computer models employed in the context of astrobiology describe phenomena either on an atomic scale (in the order of nanometres) or on a geochemical scale (in the order of hundreds of kilometres). Our group has been working for some years on astrobiological simulations, on a scale that has so far been little considered: the order of tens or hundreds of microns (Micca Longo and Longo, 2017; Micca Longo and Longo, 2018; Micca Longo et al ., 2019). At this scale, the phenomena described might be accessible to a microscope.…”

Plasma Modeling and Prebiotic Chemistry: A Review of the State-of-the-Art and Perspectives

“…The so-called delivery, that is, the actual transport of molecules from space to Earth, represents the key point of the Panspermia theory [ 7 , 8 , 9 , 10 , 11 ]. It was demonstrated that carbonate and sulfate micrometeoroids (especially calcite and anhydrite) may act as good prebiotic molecule carriers [ 12 , 13 , 14 ], in view of the well-known association between carbonates/sulfates and organic matter presence [ 15 , 16 , 17 , 18 ]. Recently, the role of the chemical composition of the primordial atmosphere was pointed out, in the context of the atmospheric entry of the aforementioned carbonate and sulfate micrometeoroids [ 19 ].…”