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Keywords = stick-like
Journal = Geosciences

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18 pages, 7696 KiB  
Article
Ichnofossils, Cracks or Crystals? A Test for Biogenicity of Stick-Like Structures from Vera Rubin Ridge, Mars
by Andrea Baucon, Carlos Neto De Carvalho, Fabrizio Felletti and Roberto Cabella
Geosciences 2020, 10(2), 39; https://doi.org/10.3390/geosciences10020039 - 21 Jan 2020
Cited by 7 | Viewed by 13275
Abstract
New images from Mars rover Curiosity display millimetric, elongate stick- like structures in the fluvio-lacustrine deposits of Vera Rubin Ridge, the depositional environment of which has been previously acknowledged as habitable. Morphology, size and topology of the structures are yet incompletely known and [...] Read more.
New images from Mars rover Curiosity display millimetric, elongate stick- like structures in the fluvio-lacustrine deposits of Vera Rubin Ridge, the depositional environment of which has been previously acknowledged as habitable. Morphology, size and topology of the structures are yet incompletely known and their biogenicity remains untested. Here we provide the first quantitative description of the Vera Rubin Ridge structures, showing that ichnofossils, i.e., the product of life-substrate interactions, are among their closest morphological analogues. Crystal growth and sedimentary cracking are plausible non-biological genetic processes for the structures, although crystals, desiccation and syneresis cracks do not typically present all the morphological and topological features of the Vera Rubin Ridge structures. Morphological analogy does not necessarily imply biogenicity but, given that none of the available observations falsifies the ichnofossil hypothesis, Vera Rubin Ridge and its sedimentary features are here recognized as a privileged target for astrobiological research. Full article
(This article belongs to the Section Biogeosciences)
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20 pages, 2986 KiB  
Article
Selective Aggregation Experiments on Planetesimal Formation and Mercury-Like Planets
by Gerhard Wurm
Geosciences 2018, 8(9), 310; https://doi.org/10.3390/geosciences8090310 - 21 Aug 2018
Cited by 5 | Viewed by 5107
Abstract
Much of a planet’s composition could be determined right at the onset of formation. Laboratory experiments can constrain these early steps. This includes static tensile strength measurements or collisions carried out under Earth’s gravity and on various microgravity platforms. Among the variety of [...] Read more.
Much of a planet’s composition could be determined right at the onset of formation. Laboratory experiments can constrain these early steps. This includes static tensile strength measurements or collisions carried out under Earth’s gravity and on various microgravity platforms. Among the variety of extrasolar planets which eventually form are (Exo)-Mercury, terrestrial planets with high density. If they form in inner protoplanetary disks, high temperature experiments are mandatory but they are still rare. Beyond the initial process of hit-and-stick collisions, some additional selective processing might be needed to explain Mercury. In analogy to icy worlds, such planets might, e.g., form in environments which are enriched in iron. This requires methods to separate iron and silicate at early stages. Photophoresis might be one viable way. Mercury and Mercury-like planets might also form due to the ferromagnetic properties of iron and mechanisms like magnetic aggregation in disk magnetic fields might become important. This review highlights some of the mechanisms with the potential to trigger Mercury formation. Full article
(This article belongs to the Special Issue Detection and Characterization of Extrasolar Planets)
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