The Lost City Hydrothermal Field: A Spectroscopic and Astrobiological Analogue for Nili Fossae, Mars

Our plain-English summary of The Lost City Hydrothermal Field: A Spectroscopic and Astrobiological Analogue for Nili Fossae, Mars, by E.S. Amador, J.L. Bandfield, W.J. Brazelton, et al (Astrobiology, 2017).

The study

• Authors: E.S. Amador, J.L. Bandfield, W.J. Brazelton, D. Kelley
• Journal: Astrobiology
• Published: 2017;17(11):1138-1160
• Cited by: 7 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Low-temperature serpentinization is a critical process with respect to Earth's habitability and the Solar System. Exothermic serpentinization reactions commonly produce hydrogen as a direct by-product and typically produce short-chained organic compounds indirectly. Here, we present the spectral and mineralogical variability in rocks from the serpentine-driven Lost City Hydrothermal Field on Earth and the olivine-rich region of Nili Fossae on Mars. Near- and thermal-infrared spectral measurements were made from a suite of Lost City rocks at wavelengths similar to those for instruments collecting measurements of the martian surface. Results from Lost City show a spectrally distinguishable suite of Mg-rich serpentine, Ca carbonates, talc, and amphibole minerals. Aggregated detections of low-grade metamorphic minerals in rocks from Nili Fossae were mapped and yielded a previously undetected serpentine exposure in the region. Direct comparison of the two spectral suites indicates similar mineralogy at both Lost City and in the Noachian (4-3.7 Ga) bedrock of Nili Fossae, Mars. Based on mapping of these spectral phases, the implied mineralogical suite appears to be extensive across the region. These results suggest that serpentinization was once an active process, indicating that water and energy sources were available, as well as a means for prebiotic chemistry during a time period when life was first emerging on Earth. Although the mineralogical assemblages identified on Mars are unlikely to be directly analogous to rocks that underlie the Lost City Hydrothermal Field, related geochemical processes (and associated sources of biologically accessible energy) were once present in the subsurface, making Nili Fossae a compelling candidate for a once-habitable environment on Mars. Key Words: Mars-Habitability-Serpentinization-Analogue. Astrobiology 17, 1138-1160.

In plain English

This was a geology and planetary-science study; it did not examine human exposure, disease, or whether the minerals occurred as fibers. The authors measured 15 rocks with infrared spectroscopy and compared them with spacecraft data from Nili Fossae, Mars. The rocks were collected in 2003 from the Lost City Hydrothermal Field, a deep-sea vent site. The serpentinite samples were dominated by serpentine minerals, mostly lizardite. Chrysotile was typically the main serpentine mineral in the fault rocks and altered gabbro (about 7 percent by volume in the gabbro). One fault rock was modeled as 40 percent amphibole by volume, mainly tremolite and actinolite. On Mars, the authors identified a new serpentine-bearing exposure. One image contained four spectral types: olivine, serpentine, carbonate, and one that could be talc, saponite or amphibole, which the data cannot distinguish. The authors concluded that Nili Fossae, where this mineral grouping was documented, is a compelling site to search for evidence of past life. They noted that remote data alone cannot show whether life existed there and that their spectral library was likely incomplete.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory infrared spectroscopy of rock samples (thermal-infrared and near-infrared), compared with analysis of orbital near-infrared spectral images of Mars
• Who was studied: 15 rock samples (serpentinites, gabbros, fault rocks, carbonates and pelagic top-layer rocks) collected by the submersible Alvin in 2003 at the Lost City Hydrothermal Field, Mid-Atlantic Ridge; plus 80 CRISM images of Nili Fossae, Mars, acquired after 2011
• Exposure: No human or animal exposure was studied, and fiber form was not assessed. The study measured minerals in rocks, including the serpentine minerals lizardite, antigorite and chrysotile, and the amphiboles tremolite, actinolite, hornblende and anthophyllite.
• Main results:
  • In the Lost City serpentinite rocks, the main serpentine mineral was lizardite, except in serpentine spectral type C.
  • Serpentinite spectral type D was modeled as about 86 vol % serpentine, mainly lizardite (about 55 vol %) and antigorite (about 31 vol %).
  • Chrysotile was typically the main serpentine mineral in the fault rocks and the metagabbro.
  • The gabbro sample's modeled spectrum included minor chrysotile, about 7 vol %.
  • The amphibole-rich fault rock was modeled as 40 vol % amphibole, primarily tremolite and actinolite.
  • The talc-rich fault rock was modeled as approximately 42 vol % talc and 21 vol % saponite.
  • The talc-rich fault rock, amphibole-rich fault rock and gabbro looked extremely similar in near-infrared measurements, so near-infrared alone could not distinguish them.
  • Brucite and magnetite, minerals expected from serpentinization, were not found in the modeled mineralogy.
  • On Mars, the authors identified one of the three serpentine-bearing exposures known in the Nili Fossae region (the other two were from an earlier study).
  • One CRISM image of Nili Fossae contained four spectral types: olivine, serpentine, carbonate, and a type that could be talc, saponite or amphibole.
  • Near-infrared reflectance data at these wavelengths cannot distinguish talc or saponite from amphiboles such as tremolite or actinolite.
• The authors' conclusion: The authors concluded that Nili Fossae, specifically where the local grouping of minerals they presented was documented, is a compelling site to search for evidence of past life on Mars. They also stated that remote sensing data alone cannot determine whether life inhabited these systems.
• Limitations the authors state:
  • The reference spectral library was likely incomplete for some samples.
  • Mineral amounts were not calculated for the carbonate and pelagic top-layer rocks because of their texture.
  • The modeling method has a detection limit of about 5 to 7 percent by volume under optimal conditions.
  • The authors note major differences between Lost City and Nili Fossae, including likely different starting fluid compositions.
  • On Mars, it is unclear whether surfaces with the talc/saponite-like signal represent a single mineral or a combination of minerals that cannot be told apart spectrally.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile.

Medical terms in this study, explained in our Lexicon: Serpentinization, Serpentine Group, Olivine, Talc, Amphibole Group, Mineralogy.

Related studies

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• Effect of secondary phase formation on the carbonation of olivine — H.E. King, O. Plümper, et al. (2010)
• Sources of organic nitrogen at the serpentinite-hosted Lost City hydrothermal field — S.Q. Lang, G.L. Früh-Green, et al. (2013)
• Division for Planetary Sciences meeting: Martian methane: rocky birth, then gone with the wind? — G. Schilling (2005)
• Cytotoxicity of respirable dusts from industrial minerals: comparison of two naturally occurring and two man-made silicates — D. Nadeau, L. Fouquette-Couture, et al. (1987)
• Rat lung reactivity to natural and man-made fibrous silicates following short-term exposure — I. Lemaire, P.G. Dionne, et al. (1989)

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