¹Benjamin Bultel,^1,2Jean‐Christophe Viennet,³François Poulet,³John Carter,¹Stephanie C. Werner
Journal of Geophysical Research Planets (in Press) Link top Article [https://doi.org/10.1029/2018JE005845]
¹ Centre for Earth Evolution and Dynamics (CEED), Department for Geosciences, University of Oslo, Norway Oslo, Norway
¹ Laboratoire d’Archéologie Moléculaire et Structurale, CNRS UMR 8220, UPMC – 4 place Jussieu, 75005 Paris and Institut de Minéralogie, Physique des Matériaux et Cosmochimie, IMPMC, Sorbonne Universités, CNRS UMR 7590, Muséum National d’Histoire Naturelle, MNHN, UPMC, IRD UMR 206, Paris, France
¹ Institut d’Astrophysique Spatiale, Université Paris‐Sud, Orsay, France
Published by arrangement with John Wiley & Sons

Noachian surfaces on Mars exhibit vertical assemblages of weathering horizons termed as weathering profiles; this indicates that surface water caused alteration of the rocks which required a different, warmer climate than today. Evidence of this early martian climate with CO2 vapor as the main component causing greenhouse warming has been challenged by the lack of carbonate in these profiles. Here we report the analysis of CRISM L‐detector data leading to the detections of carbonates using a spectral signature exclusively attributed to them. The carbonates are collocated with hydroxylated minerals in weathering profiles over the martian surface. The origin of CO2 for the formation of carbonates could be the atmosphere. The widespread distribution of weathering profiles with carbonates over the surface of the planet suggest global interactions between fluids containing carbonate/bicarbonate ions with the surface of Mars in the presence of atmospheric water until around 3.7 billion years ago. Please also see the Supporting Information for a graphical abstract.

¹William Herbst,²James P.Greenwood
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2019.03.039]
¹Astronomy Department, Wesleyan University, Middletown, CT 06459, United States of America
²Earth & Environmental Sciences Department, Wesleyan University, Middletown, CT 06459, United States of America
Copyright Elsevier

We propose that chondrules and chondrites formed together during a brief radiative heating event caused by the close encounter of a small (m to km-scale), primitive planetesimal (SPP) with incandescent lava on the surface of a large (100 km-scale) differentiated planetesimal (LDP). In our scenario, chondrite lithification occurs by hot isostatic pressing (HIP) simultaneously with chondrule formation, in accordance with the constraints of complementarity and cluster chondrites. Thermal models of LDPs formed near t = 0 predict that there will be a very narrow window of time, coincident with the chondrule formation epoch, during which crusts are thin enough to frequently rupture by impact, volcanism and/or crustal foundering, releasing hot magma to their surfaces. The heating curves we calculate are more gradual and symmetric than the “flash heating” characteristic of nebular models, but in agreement with the constraints of experimental petrology. The SPP itself is a plausible source of the excess O, Na and Si vapor pressure (compared to a solar nebula environment) that is required by chondrule observations. Laboratory experiments demonstrate that FeO-poor porphyritic olivine chondrules, the most voluminous type of chondrule, can be made using heating and cooling curves predicted by the “flyby” model. If chondrules are a by-product of chondrite lithification, then their high volume abundance within well-lithified chondritic material is not evidence that they were once widespread within the Solar System. Relatively rare events, such as the flybys modeled here, could account for their abundance in the meteorite record.

Christian T. Lenz^1,3, Hubert Klahr¹, and Tilman Birnstiel²
Astrophysical Journal 874, 36 Link to Article [DOI: 10.3847/1538-4357/ab05d9 ]
¹Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg, Germany
²University Observatory, Faculty of Physics, Ludwig-Maximilians-Universität München, Scheinerstr. 1, D-81679 Munich, Germany
³Member of the International Max Planck Research School for Astronomy and Cosmic Physics at the Heidelberg University.

We propose an expression for a local planetesimal formation rate proportional to the instantaneous radial pebble flux. The result—a radial planetesimal distribution—can be used as an initial condition to study the formation of planetary embryos. We follow the idea that one needs particle traps to locally enhance the dust-to-gas ratios sufficiently, such that particle gas interactions can no longer prevent planetesimal formation on small scales. The locations of these traps can emerge everywhere in the disk. Their occurrence and lifetime is subject to ongoing research; thus, here they are implemented via free parameters. This enables us to study the influence of the disk properties on the formation of planetesimals, predicting their time-dependent formation rates and the location of primary pebble accretion. We show that large α-values of 0.01 (strong turbulence) prevent the formation of planetesimals in the inner part of the disk, arguing for lower values of around 0.001 (moderate turbulence), at which planetesimals form quickly at all places where they are needed for proto-planets. Planetesimals form as soon as dust has grown to pebbles (mm to dm) and the pebble flux reaches a critical value, which is after a few thousand years at 2–3 au and after a few hundred thousand years at 20–30 au. Planetesimal formation lasts until the pebble supply has decreased below a critical value. The final spatial planetesimal distribution is steeper compared to the initial dust and gas distribution, which helps explain the discrepancy between the minimum mass solar nebula and viscous accretion disks.