Divulgazione scientifica

A view of extraterrestrial soils


G. Certini1, R. Scalenghe2 & R. Amundson3

1Dipartimento di Scienza del Suolo e Nutrizione della Pianta, UniversitÓ degli Studi di Firenze, P.za delle Cascine 28, 50144 Firenze
2Dipartimento di Agronomia Ambientale e Territoriale, UniversitÓ degli Studi di Palermo, V.le delle Scienze 13, 90128 Palermo
3Division of Ecosystem Sciences, University of California, Berkeley, CA 94720, USA

European Journal of Soil Science, December 2009, 60, 1078–1092


Correspondence to G. Certini: certini@unifi.it





The nature of soils on celestial bodies other than Earth is a growing area of research in planetary geology. However, disagreement over the significance of these deposits arises, in part, through the lack of a unified concept and definition of soil in the literature. The pragmatic definition 'medium for plant growth' is taken by some to imply the necessity of biota for soil to exist, and has been commonly adopted in the planetary science community. In contrast, a more complex and informative definition is based on scientific theory: soil is the (bio)geochemically/physically altered material at the surface of a planetary body that encompasses surficial extraterrestrial telluric deposits. This definition is based on the premise that soil is a body that retains information about its environmental history and that it does not need the presence of life to form. Four decades of missions have gathered geochemical information regarding the surface of planets and bodies within the Solar System, and information is quickly increasing. Reviewing the current knowledge on properties of extraterrestrial regoliths, we conclude that the surficial deposits of Venus, Mars and our moon should be considered to be soils in a pedological sense, and that Mercury and some large asteroids are covered in mantles that are soil candidates. A key environmental distinction between Earth and other Solar System bodies is the presence of life, and because of this dissimilarity in soil-forming processes, it is reasonable to distinguish these (presently) abiotic soils as Astrosols. Attempts to provide detailed classifications of extraterrestrial soils are premature, given our poor current knowledge of the Universe, but they highlight the fact that Earth possesses almost-abiotic environments that lend themselves to providing more understanding about telluric bodies of the Solar System.

"He found himself in the neighbourhood of the asteroids 325, 326, 327, 328, 329, and 330. He began, therefore, by visiting them, in order to add to his knowledge."

(Excerpt from the The Little Prince by Antoine de Saint-ExupÚry)

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