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Thermal decomposition rate of MgCO3 as an inorganic astrobiological matrix in meteorites

Published online by Cambridge University Press:  13 April 2016

E. Bisceglia ,
G. Micca Longo  and
S. Longo
E. Bisceglia
Affiliation:
Dipartimento di Chimica, Università degli Studi di Bari, via Orabona 4, I-70126 Bari, Italy
G. Micca Longo
Affiliation:
Dipartimento di Chimica, Università degli Studi di Bari, via Orabona 4, I-70126 Bari, Italy CNR-NANOTEC, Bari section, via Amendola 122/D, I-70126 Bari, Italy
S. Longo*
Affiliation:
Dipartimento di Chimica, Università degli Studi di Bari, via Orabona 4, I-70126 Bari, Italy CNR-NANOTEC, Bari section, via Amendola 122/D, I-70126 Bari, Italy INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy e-mail: e.bisceglia2@studenti.uniba.itgaia.miccalongo@nanotec.cnr.it
*
savino.longo@nanotec.cnr.it
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Abstract

Carbonate minerals, likely of hydrothermal origins and included into orthopyroxenite, have been extensively studied in the ALH84001 meteorite. In this meteorite, nanocrystals comparable with those produced by magnetotactic bacteria have been found into a carbonate matrix. This leads naturally to a discussion of the role of such carbonates in panspermia theories. In this context, the present work sets the basis of a criterion to evaluate whether a carbonate matrix in a meteor entering a planetary atmosphere would be able to reach the surface. As a preliminary step, the composition of carbonate minerals in the ALH84001 meteorite is reviewed; in view of the predominance of Mg in these carbonates, pure magnesite (MgCO3) is proposed as a mineral model. This mineral is much more sensitive to high temperatures reached during an entry process, compared with silicates, due to facile decomposition into MgO and gaseous carbon dioxide (CO2). A most important quantity for further studies is therefore the decomposition rate expressed as CO2 evaporation rate J (molecules/m2 s). An analytical expression for J(T) is given using the Langmuir law, based on CO2 pressure in equilibrium with MgCO3 and MgO at the surface temperature T. Results suggest that carbonate minerals rich in magnesium may offer much better thermal protection to embedded biological matter than silicates and significantly better than limestone, which was considered in previous studies, in view of the heat absorbed by their decomposition even at moderate temperatures. This first study can be extended in the future to account for more complex compositions, including Fe and Ca.

Keywords

CarbonatesLangmuir lawmeteorspanspermia
Type
Research Article
Information
International Journal of Astrobiology , Volume 16 , Issue 2 , April 2017 , pp. 130 - 136
Copyright
Copyright © Cambridge University Press 2016 

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