Rev Environ Sci Biotechnol (2006) 5:219–231 DOI 10.1007/s11157-006-0008-x REVIEW PAPER Astrobiological significance of minerals on Mars surface environment Jesus Martinez-Frias Æ Gabriel Amaral Æ Luis Va´zquez Received: 7 December 2005 / Accepted: 25 May 2006 / Published online: 14 July 2006 Ó Springer Science+Business Media B.V. 2006 Abstract Despite the large amount of geomor- mineral parageneses on earth (in particular in the phological, geodynamic and geophysical data context of some selected terrestrial analogues), obtained from Mars missions, much is still un- and (3) to show that their differential UV known about Martian mineralogy and parage- shielding properties, against the hostile environ- netic assemblages, which is fundamental to an mental conditions of the Martian surface, are of a understanding of its entire geological history. great importance for the search for extraterres- Minerals are not only indicators of the physical– trial life. chemical settings of the different environments and their later changes, but also they could (and Keywords Mars minerals Æ Extreme do) play a crucial astrobiological role related with environment Æ Astrobiology Æ UV radiation Æ the possibility of existence of extinct or extant Jarosite Æ Gypsum Æ Sulfates Martian life. This paper aims: (1) to present a synoptic review of the main water-related Mar- tian minerals (mainly jarosite and other sulfates) Introduction discovered up to the present time; (2) to empha- size their significance as environmental geomar- Over the last half century, Mars has been ex- kers, on the basis of their geological settings and plored with telescopes, spacecrafts and robotic rovers. All the information obtained from these J. Martinez-Frias (&) Æ L. Va´zquez different sources, along with the results obtained Centro de Astrobiologı´a (CSIC-INTA), 28850 by the study of SNC meteorites and terrestrial Torrejo´ n de Ardoz, Madrid, Spain analogs, is starting to reveal the geological e-mail: [email protected] diversity of the planet and provides data for the- G. Amaral orizing about how the different Martian envi- Departamento de Quı´mica Fı´sica I, Facultad de ronments evolved. Although it is well known that Ciencias Quı´micas, Universidad Complutense, 28040 liquid water is not stable at the surface under Madrid, Spain e-mail: [email protected] today’s atmospheric conditions (e.g., Ingersoll 1970; Hecht 2002), there is significant evidence L. Va´zquez that Mars once had a thicker atmosphere, that Departamento de Matema´tica Aplicada, Facultad de liquid water may have been much more abundant Informa´tica, Universidad Complutense de Madrid, 28040 Madrid, Spain on the surface and in the subsurface earlier in e-mail: [email protected] Martian history, that it has at least sporadically 123 220 Rev Environ Sci Biotechnol (2006) 5:219–231 flowed on the Martian surface, and that it may Martian environment and its possible association even still be present in the subsurface today (e.g., with other liquid water-related minerals (e.g. Sagan and Mullen 1972; Carr et al. 1977; Cess gypsum) indubitably stresses its astrobiological et al. 1980; Squyres et al. 1992; Mckay and Stoker interest. 1989; Malin and Edgett 2000; Feldman et al. 2002; This paper aims: (1) to present a synoptic Boynton et al. 2002; Mitrofanov et al. 2002; Cos- review of the main water-related Martian minerals tard et al. 2002; Noe Dobrea et al. 2003; Squyres discovered till the present; (2) to emphasize their et al. 2004; Klingelho¨ fer et al. 2004; Madden significance as environmental geomarkers, on the et al. 2004; Christensen et al. 2004; Orofino et al. basis of their geological settings and mineral par- 2005; Glotch and Christensen 2005, among oth- ageneses on earth (in particular in the context of ers). However, despite the huge amount of geo- some selected terrestrial analogues), and (3) to morphological, geodynamic and geophysical data show that their differential UV shielding proper- obtained: (a) there is a clear ambiguity in inter- ties, against the hostile environmental conditions preting certain geological features of the Martian of the Mars surface, are of a great importance for surface, and (b) much is still unknown about Mars the search for extraterrestrial life. mineralogy and paragenetic assemblages, which is fundamental to an understanding of its whole geological history. Minerals are not only indicators Mineralogy and UV radiation on the surface of the physical–chemical settings of the different of Mars environments and their later changes, but also they could (and do) play a crucial astrobiological role The Martian regolith is made up of an apparently related with the possibility of existence of extinct homogenized dust having (broadly) basaltic or extant Martian life. If thirty years ago Viking composition, with admixed local rock compo- landers provided the first elemental analyses of nents, oxides (e.g. hematite), water-bearing Martian surface materials, the detection of an iron phyllosilicates and salts (mainly sulfates). Quar- mineral (gray crystalline hematite) by the Mars tzofeldspathic materials also have been identified Global Surveyor Thermal Emission Spectrometer (Bandfield et al. 2004). Information from scien- (MGS-TES) (Christensen et al. 2000, 2001; Pear- tific literature about past Mars missions, together son et al. 2000) led to the selection of Meridiani with recent reviews and new findings (see for in- Planum as one of the landing sites of the two stance Souza et al. 2004; McSween 2004; Vani- NASA’s Mars Exploration Rovers (MERs). In man et al. 2004; Lane et al. 2004; Squyres and 2004, the Mars Exploration Rover Opportunity’s Knoll 2005; Clark et al. 2005; Poulet et al. 2005; Moessbauer spectrometer obtained new straight- Yen et al. 2005; Hutchinson et al. 2005) indicate a forward evidence that, at least in Meridiani mineralogical composition of the Martian surface, Planum, the formation of hematite involved an which displays, in broad terms, the following aqueous mechanism. Hematite at Meridiani general distribution: silicates and oxides (mainly Planum consists essentially of spherules inter- olivine (Mg2SiO4 to Fe2SiO4), pyroxenes (Ca preted as concretions that have weathered out of a (Mg, Fe, Al)(Al, Si)2O6) and plagioclases (Na, sulfate-rich outcrop. In addition, hematite is also a Ca)(Si, Al)4O8 (87–79%)); hematite, Fe2O3, component of the outcrop matrix material. It also goethite, FeO(OH), sulfate salts (jarosite, indicated the presence of an iron-bearing mineral KFe3(SO4)2(OH)6, kieserite, MgSO4 Æ H2O, and called jarosite in the set of rocks dubbed ‘‘El very possibly also some polyhydrated sulfates: Capitan’’ (Squyres et al. 2004; Klingelho¨ fer et al. epsomite, MgSO4 Æ 7H2O, hexahydrite, 2004; Madden et al. 2004; Christensen et al. 2004; MgSO4 Æ 6H2O, pentahydryte, MgSO4 Æ 5H2O, Glotch and Christensen 2005). ‘‘El Capitan’’ is starkyite, MgSO4 Æ 4H2O, (12%) [Zhu et al. located within the rock outcrop that lines the inner (2006), Bibring et al. (2006), as well as, possibly, edge of the small crater where Opportunity szomolnokite and ferricopiapite] (Lane et al. landed. The exciting discovery of jarosite indicates (2004); and carbonates (Banfield et al. 2003) the existence of an ancient extreme (acidic) (0–4%), chloride salts (1%), nitrates (0–1%), 123 Rev Environ Sci Biotechnol (2006) 5:219–231 221 water (>1%, may be much higher). Poulet (2005) variably enriched in bromine relative to chlorine, detected the presence of phyllosilicates in the indicating a past interaction with water (Fan and ancient Martian highlands. These authors suggest Schulze-Makuch 2005). Generally, Martian bas- that Earth-like conditions existed well before alts are composed of plagioclase, feldspar, clino- 3.5–4 billion years ago. During later martian his- pyroxene, olivine, plus/minus sheet silicates and tory, it seems that the surface became more occur primarily in the equatorial to mid-latitude acidic, suppressing the formation of phyllosili- southern highlands regions (Banfield 2002). Ma- cates and carbonates, and leading to the haema- jor surface geological units of the ancient crust tite and sulfates spectacularly observed at consist of pyroxenes and plagioclase, with varying Meridiani by Opportunity. Very recently, Zhu proportions of olivine and alteration minerals. et al. (2006) suggest the existence of other min- Moreover, Martian (SNC) meteorites display eral phases, such as calcopyrite, covellite, garnet small amounts of secondary minerals (clays, (uvarovite, almandine) and thenardite. Marion carbonates, halides, sulfates) probably formed by et al. (2006) developed a model, parameterized reaction with subsurface fluids. for the Na–K–Mg–Ca–Fe–H–Cl–SO4–NO3–OH– In accordance with Patel et al. (2004) the study HCO3–CO3–CO2–CH4–H2O system, which of solar ultraviolet (UV) radiation is of extreme includes 81 solid phases. Their simulation sug- importance in a wide range of scientific disci- gests the possible existence, among others, of plines, with UV radiation playing an important melanterite, rozenite, mirabilite, szomolnokite role in organic and chemical evolution and also as and schwertmanite. a major constraint in biological evolution. Unlike Infrared observations display evidence for Earth, there is a significant amount of UV flux on igneous diversity and magmatic evolution on Mars, mainly due to the influence of the shorter Mars (Christensen et al. 2005). wavelengths UVC (100–280 nm) and UVB The very recent MEX-OMEGA results have (280–315 nm). On the surface of Mars solar shed light on the discussion about the mineral- radiation which penetrates the thin atmosphere at ogical and petrological characteristics of Mars wavelengths between 200 and 400 nm is capable surface. However, in accordance with Wyatt and of interacting directly with biological structures McSween (2002) we agree that controversy still and causing severe damage. Various works on the remains (and probably it will be necessary to biological effects of UV radiation (Cockell 1998; improve ‘‘in situ’’ analysis’’) about the existence Cockell et al. 2000; Ronto´ et al.