N. Mari^a, A.J.V. Riches^b, L.J. Hallis^a, Y. Marrocchi^c, J. Villeneuve^c, P. Gleissner^d, H. Becker^d M.R. Lee^a
Geochimica et Cosmochimcia Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.05.025]
^aSchool of Geographical and Earth Sciences, University of Glasgow, University Avenue, Glasgow, G12 8QQ, UK
^bDepartment of Earth Sciences, Durham University, Stockton Road, Durham, DH1 3LE, UK
^cCentre de Recherches Pétrographiques et Géochimiques, CNRS, Université de Lorraine, UMR 7358, Vandoeuvre-lès-Nancy, 54501, France
^dFreie Universität Berlin, Institut für Geologische Wissenschaften, Kaiserswerther Str. 16-18, 14195, Berlin, Germany
Copyright Elsevier

Martian lava flows likely acquired S-rich material from the regolith during their emplacement on the planet’s surface. We investigated five of the twenty known nakhlites (Nakhla, Lafayette, Miller Range (MIL) 090032, Yamato 000593, and Yamato 000749) to determine whether these lavas show evidence of regolith assimilation, and to constrain the potential implications that this process has on chemical tracing of martian mantle source(s). To establish the proportionate influence of atmospheric, hydrothermal, and volcanic processes on nakhlite isotopic systematics we obtained in situ sulphur isotope data (Δ³³S and δ³⁴S) for sulphide grains (pyrrhotite and pyrite) in all five nakhlite samples. For Nakhla, Lafayette, and MIL 090032, these data are integrated with highly siderophile element (HSE) abundances and Os-isotope compositions, as well as textural information constrained prior to isotopic analysis. This work thereby provides the first Re-Os isotope systematics for two different nakhlites, and also the first Re-Os isotope data for martian sample for which detailed petrographic information was constrained prior to digestion.

We report the largest variation in δ³⁴S yet found in martian meteorites (-13.20 ‰ to +15.16 ‰). The relatively positive Δ³³S and δ³⁴S values of MIL 090032 (δ³⁴S = +10.54 ± 0.09 ‰; Δ³³S = -0.67 ± 0.10 ‰) indicate this meteorite assimilated sulphur affected by UV-photochemistry. In contrast, the strongly negative values of Lafayette (δ³⁴S = -10.76 ± 0.14 ‰; Δ³³S = -0.09 ± 0.12 ‰) are indicative of hydrothermal processes on Mars. Nakhla, Yamato 000593, and Yamato 000749 sulphides have a narrower range of sulphur isotope compositions (Δ³³S and δ³⁴S ∼ 0) that is consistent with no assimilation of martian surface materials during lava flow emplacement. Consequently we used this second group of Δ³³S values to approximate the Δ³³S of the nakhlite source, yielding a Δ³³S value of -0.1 ‰.

Nakhlite HSE patterns result from a sulphide-saturated melt where Ru-Os-Ir alloys/sulphide were likely crystallized during earlier phases of magmatic processing in Mars to result in the fractionated HSE patterns of the nakhlites. Our data, alongside a synthesis of previously published data, suggest assimilation of an enriched component to the primary nakhlite melt, potentially a late-stage crystallization cumulate from the martian magma ocean stage. In the context of this model, and within large uncertainties, our data hint at perturbation and potential decoupling of nakhlite Re-Os isotope systematics from other isotopic systems as a result of small degrees of assimilation of a regolith component with highly radiogenic ¹⁸⁷Os/¹⁸⁸Os.

John M. Brewer^1,2, Songhu Wang¹, Debra A. Fischer¹, and Daniel Foreman-Mackey³
Astrophysical Journal Letters 867, L3 Link to Article [DOI: 10.3847/2041-8213/aae710]
¹Department of Astronomy, Yale University, 52 Hillhouse Avenue, New Haven, CT 06511, USA
²Department of Astronomy, Columbia University, 550 West 120th Street, New York, NY 10027, USA
³Flatiron Institute, 162 5th Avenue, New York, NY 10010, USA

In systems with detected planets, hot Jupiters and compact systems of multiple planets are nearly mutually exclusive. We compare the relative occurrence of these two architectures as a fraction of detected planetary systems to determine the role that metallicity plays in planet formation. We show that compact multi-planet systems occur more frequently around stars of increasingly lower metallicities using spectroscopically derived abundances for more than 700 planet hosts. At higher metallicities, compact multi-planet systems comprise a nearly constant fraction of the planet hosts despite the steep rise in the fraction of hosts containing hot and cool Jupiters. Since metal-poor stars have been underrepresented in planet searches, this implies that the occurrence rate of compact multis is higher than previously reported. Due to observational limits, radial velocity planet searches have focused mainly on high-metallicity stars, where they have a higher chance of finding giant planets. New extreme-precision radial velocity instruments coming online that can detect these compact multi-planet systems can target lower-metallicity stars to find them.

C. J. Clarke¹ et al. (>10)
Astrophysical Journal Letters 866, L6 Link to Article [DOI: 10.3847/2041-8213/aae36b]
¹Institute of Astronomy, Madingley Road, Cambridge CB3 OHA, UK

We present high-resolution millimeter continuum imaging of the disk surrounding the young star CI Tau, a system hosting the first hot Jupiter candidate in a protoplanetary disk system. The system has extended mm emission on which are superposed three prominent annular gaps at radii ~13, 39, and 100 au. We argue that these gaps are most likely to be generated by massive planets so that, including the hot Jupiter, the system contains four gas giant planets at an age of only 2 Myr. Two of the new planets are similarly located to those inferred in the famous HL Tau protoplanetary disk; in CI Tau, additional observational data enables a more complete analysis of the system properties than was possible for HL Tau. Our dust and gas dynamical modeling satisfies every available observational constraint and points to the most massive ensemble of exoplanets ever detected at this age, with its four planets spanning a factor 1000 in orbital radius. Our results show that the association between hot Jupiters and gas giants on wider orbits, observed in older stars, is apparently in place at an early evolutionary stage.