title: Self-assembling iron oxyhydroxide/oxide tubular structures: laboratory-grown and field examples from Rio Tinto.
abstract: Rio Tinto in southern Spain has become of increasing astrobiological significance, in particular for its similarity to environments on early Mars. We present evidence of tubular structures from sampled terraces in the stream bed at the source of the river, as well as ancient, now dry, terraces. This is the first reported finding of tubular structures in this particular environment. We propose that some of these structures could be formed through self-assembly via an abiotic mechanism involving templated precipitation around a fluid jet, a similar mechanism to that commonly found in so-called chemical gardens. Laboratory experiments simulating the formation of self-assembling iron oxyhydroxide tubes via chemical garden/chemobrionic processes form similar structures. Fluid-mechanical scaling analysis demonstrates that the proposed mechanism is plausible. Although the formation of tube structures is not itself a biosignature, the iron mineral oxidation gradients across the tube walls in laboratory and field examples may yield information about energy gradients and potentially habitable environments.
authors.affiliation: NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA; NASA Astrobiology Institute, Icy Worlds, Pasadena, CA 91109, USA.
authors.forename: Laura M
authors.initials: LM
authors.lastname: Barge
authors.affiliation: Department of Chemical Engineering and Biotechnology , University of Cambridge , Cambridge CB2 3RA , UK.
authors.forename: Silvana S S
authors.identifier: 0000-0003-0417-035X
authors.initials: SS
authors.lastname: Cardoso
authors.affiliation: Instituto Andaluz de Ciencias de la Tierra, IACT, CSIC-UGR, Av. de las Palmeras, 4, 18100 Armilla, Granada, Spain; Instituto Carlos I de Física Teórica y Computacional, Universidad de Granada, 18071 Granada, Spain.
authors.forename: Julyan H E
authors.identifier: 0000-0001-7392-0957
authors.initials: JH
authors.lastname: Cartwright
authors.affiliation: NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA; NASA Astrobiology Institute, Icy Worlds, Pasadena, CA 91109, USA.
authors.forename: Ivria J
authors.initials: IJ
authors.lastname: Doloboff
authors.affiliation: NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA; NASA Astrobiology Institute, Icy Worlds, Pasadena, CA 91109, USA.
authors.forename: Erika
authors.initials: E
authors.lastname: Flores
authors.affiliation: Instituto Andaluz de Ciencias de la Tierra, IACT, CSIC-UGR, Av. de las Palmeras, 4, 18100 Armilla, Granada, Spain; Departamento de Estratigrafía y Paleontología, Universidad de Granada, 18071 Granada, Spain.
authors.forename: Elena
authors.identifier: 0000-0003-1569-8088
authors.initials: E
authors.lastname: Macías-Sánchez
authors.affiliation: Instituto Andaluz de Ciencias de la Tierra, IACT, CSIC-UGR , Av. de las Palmeras, 4, 18100 Armilla, Granada , Spain.
authors.forename: C Ignacio
authors.identifier: 0000-0001-8612-3826
authors.initials: CI
authors.lastname: Sainz-Díaz
authors.affiliation: Carl Sagan Center, SETI Institute, Mountain View, CA, USA; Impossible Sensing, St Louis, MO, USA.
authors.forename: Pablo
authors.initials: P
authors.lastname: Sobrón
keywords: Rio Tinto; astrobiology; chemical gardens; chemobrionics; iron oxide; tubular structures