¹Seth Redfield, ²Jay Farihi, ¹P. Wilson Cauley, ³Steven G. Parsons, ⁴Boris T. Gänsicke, ¹Girish M. Duvvuri
The Astrophysical Journal 839, 42 Link to Article [https://doi.org/10.3847/1538-4357/aa68a0]
¹Astronomy Department and Van Vleck Observatory, Wesleyan University, Middletown, CT 06459, USA
²Department of Physics and Astronomy, University College London, London WC1E 6BT, UK
³Department of Physics and Astronomy, University of Sheffield, Sheffield, S3 7RH, UK
⁴Department of Physics, University of Warwick, Coventry CV4 7AL, UK

With the recent discovery of transiting planetary material around WD 1145+017, a critical target has been identified that links the evolution of planetary systems with debris disks and their accretion onto the star. We present a series of observations, five epochs over a year, taken with Keck and the VLT, which for the first time show variability of circumstellar absorption in the gas disk surrounding WD 1145+017 on timescales of minutes to months. Circumstellar absorption is measured in more than 250 lines of 14 ions among 10 different elements associated with planetary composition, e.g., O, Mg, Ca, Ti, Cr, Mn, Fe, and Ni. Broad circumstellar gas absorption with a velocity spread of 225 km s−1 is detected, but over the course of a year blueshifted absorption disappears, while redshifted absorption systematically increases. A correlation of equivalent width and oscillator strength indicates that the gas is not highly optically thick (median τ ≈ 2). We discuss simple models of an eccentric disk coupled with magnetospheric accretion to explain the basic observed characteristics of these high-resolution and high signal-to-noise observations. Variability is detected on timescales of minutes in the two most recent observations, showing a loss of redshifted absorption for tens of minutes, coincident with major transit events and consistent with gas hidden behind opaque transiting material. This system currently presents a unique opportunity to learn how the gas causing the spectroscopic, circumstellar absorption is associated with the ongoing accretion evidenced by photospheric contamination, as well as the transiting planetary material detected in photometric observations.

^1,2Sándor Góbi, ^1,2Alexandre Bergantini, ^1,2Ralf I. Kaiser
Astrophysical Journal 838, 2 Link to Article [https://doi.org/10.3847/1538-4357/aa653f]
¹Department of Chemistry, University of Hawaii at Mānoa, Honolulu, HI 96822, USA
²W.M. Keck Laboratory in Astrochemistry, University of Hawaii at Mānoa, Honolulu, HI 96822, USA

The aim of the present work is to unravel the radiolytic decomposition of adenine (C5H5N5) under conditions relevant to the Martian surface. Being the fundamental building block of (deoxy)ribonucleic acids, the possibility of survival of this biomolecule on the Martian surface is of primary importance to the astrobiology community. Here, neat adenine and adenine–magnesium perchlorate mixtures were prepared and irradiated with energetic electrons that simulate the secondary electrons originating from the interaction of the galactic cosmic rays with the Martian surface. Perchlorates were added to the samples since they are abundant—and therefore relevant oxidizers on the surface of Mars—and they have been previously shown to facilitate the radiolysis of organics such as glycine. The degradation of the samples were monitored in situ via Fourier transformation infrared spectroscopy and the electron ionization quadruple mass spectrometric method; temperature-programmed desorption profiles were then collected by means of the state-of-the-art single photon photoionization reflectron time-of-flight mass spectrometry (PI-ReTOF-MS), allowing for the detection of the species subliming from the sample. The results showed that perchlorates do increase the destruction rate of adenine by opening alternative reaction channels, including the concurrent radiolysis/oxidation of the sample. This new pathway provides a plethora of different radiolysis products that were identified for the first time. These are carbon dioxide (CO2), isocyanic acid (HNCO), isocyanate (OCN−), carbon monoxide (CO), and nitrogen monoxide (NO); an oxidation product containing carbonyl groups (R1R2–C=O) with a constrained five-membered cyclic structure could also be observed. Cyanamide (H2N–C≡N) was detected in both irradiated samples as well.

^1,2Sean R. Scott, ^1,2Kenneth W.W. Sims, ²Bryce R. Frost, ³Peter B. Kelemen, ⁴Katy A. Evans, ²Susan M. Swapp
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2017.07.011]
¹Wyoming High Precision Isotope Laboratory, Department of Geology and Geophysics, University of Wyoming, Laramie, WY, 82072
²Department of Geology and Geophysics, University of Wyoming, Laramie, WY, 82072
³Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964
⁴Department of Applied Geology, Curtin University, GPO Box 1987, WA6845, Australia
Copyright Elsevier

The behavior of Fe during serpentinization largely controls the potential for oxidation-reduction reactions and energy budget for serpentinite-hosted microbial communities. We present Fe isotope data for mineral separates from a partially serpentinized dunite from New Caledonia to understand the behavior of Fe during serpentinization processes. Our new Fe isotope data in mineral separates is compared to existing data from whole rock studies of serpentinites, which have generally concluded that Fe mobility during serpentinization is restricted to the highest temperatures of serpentinization in subduction zones. Measurements of mineral separates from New Caledonia show significant Fe isotope fractionations, with serpentine-brucite mixtures having the lowest δ56Fe ∼ -0.35 ‰ and magnetite having the highest δ56Fe ∼ +0.75 ‰. Olivine, orthopyroxene, and the whole rock composition are all within error of δ56Fe = 0.00 ‰. Fe isotope thermometry between mineral phases reveals two distinct temperatures of equilibration, one for the mantle olivine and pyroxene (∼1325°C), and a second, much lower temperature (∼335°C) for the serpentinite assemblage. The combined isotopic, mineralogical and geochemical data indicate that during the magnetite-forming stage of serpentinization, a pore fluid in equilibrium with the mineralogical assemblage evolves to higher Fe concentrations as serpentinization proceeds. When this pore fluid is removed from the serpentinizing environment, the total abundance of Fe removed from the rock in the pore fluid is much less than the bulk rock Fe and has a minimal effect on the overall rock composition.