¹Joshua T.S. Cahill, ²Justin J. Hagerty, ¹David J. Lawrence, ¹Rachel L. Klima, ¹David T. Blewett
¹Johns Hopkins Applied Physics Laboratory, Laurel, MD
²U. S. Geological Survey, Astrogeology Science Center, Flagstaff, AZ

The Moon has areas of magnetized crust (“magnetic anomalies”), the origins of which are poorly constrained. A magnetic anomaly near the northern rim of South Pole-Aitken (SPA) basin was recently postulated to originate from remnant metallic iron emplaced by the SPA basin-forming impactor. Here, we remotely examine the regolith of this SPA magnetic anomaly with a combination of Clementine and Lunar Prospector derived iron maps for any evidence of enhanced metallic iron content. We find that these data sets do not definitively detect the hypothesized remnant metallic iron within the upper tens of centimeters of the lunar regolith.

Reference
Cahill JTS, Hagerty JJ, Lawrence DJ, Klima RL, Blewett DT (2014) Surveying the South Pole-Aitken basin magnetic anomaly for remnant impactor metallic iron. Icarus (in Press)
Link to Article [DOI: 10.1016/j.icarus.2014.08.035]

Copyright Elsevier

¹Elizabeth A. Frank, ²Bradley S. Meyer, ^1,3,4Stephen J. Mojzsis

¹Department of Geological Sciences, NASA Lunar Science Institute & Center for Lunar Origin and Evolution (CLOE), University of Colorado, 2200 Colorado Avenue, UCB 399, Boulder, Colorado 80309-0399 USA
²Department of Physics and Astronomy, Clemson University, Clemson, South Carolina
³Laboratoire de Géologie de Lyon, École Normale Supérieure de Lyon and Université Claude Bernard Lyon 1, CNRS UMR 5276, 2 rue Raphaël Dubois, 69622 Villeurbanne, France
⁴Hungarian Academy of Sciences, Institute for Geological and Geochemical Research, 45 Budaörsi ut, H-1112 Budapest, Hungary

Discoveries of rocky worlds around other stars have inspired diverse geophysical models of their plausible structures and tectonic regimes. Severe limitations of observable properties require many inexact assumptions about key geophysical characteristics of these planets. We present the output of an analytical galactic chemical evolution (GCE) model that quantitatively constrains one of those key properties: radiogenic heating. Earth’s radiogenic heat generation has evolved since its formation, and the same will apply to exoplanets. We have fit simulations of the chemical evolution of the interstellar medium in the solar annulus to the chemistry of our solar system at the time of its formation and then applied the carbonaceous chondrite/Earth’s mantle ratio to determine the chemical composition of what we term “cosmochemically Earth-like” exoplanets. Through this approach, predictions of exoplanet radiogenic heat productions as a function of age have been derived. The results show that the later a planet forms in galactic history, the less radiogenic heat it begins with; however, due to radioactive decay, today, old planets have lower heat outputs per unit mass than newly formed worlds. The long half-life of 232Th allows it to continue providing a small amount of heat in even the most ancient planets, while 40K dominates heating in young worlds. Through constraining the age-dependent heat production in exoplanets, we can infer that younger, hotter rocky planets are more likely to be geologically active and therefore able to sustain the crustal recycling (e.g. plate tectonics) that may be a requirement for long-term biosphere habitability. In the search for Earth-like planets, the focus should be made on stars within a billion years or so of the Sun’s age.

Reference
Frank EA, Meyer BS, Mojzsis SJ (2014) A radiogenic heating evolution model for cosmochemically Earth-like exoplanets. Icarus (in Press)
Link to Article [DOI: 10.1016/j.icarus.2014.08.031]

Copyright Elsevier

^1,2D.L. Nuding, ³E.G. Rivera-Valentin, ^1,4R.D. Davisa, ^1,4R.V. Gough, ⁵V.F. Chevrier, ^1,4M.A. Tolbert
¹Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder CO 80309
²Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder CO 80309
³Department of Geological Sciences, Brown University, Providence RI 02912
⁴Department of Chemistry and Biochemistry, University of Colorado, Boulder CO 80309
⁵W. M. Keck Laboratory for Space and Planetary Simulation, Arkansas Center for Space and Planetary Science, University of Arkansas, Fayetteville, AR 72701

Calcium perchlorate (Ca(ClO4)2) is a highly deliquescent salt that may exist on the surface of present-day Mars; however, its water uptake properties have not been well characterized at temperatures and relative humidity conditions relevant to Mars. Here, we quantify the deliquescent relative humidity (DRH) and efflorescent relative humidity (ERH) of Ca(ClO4)2 as a function of temperature (223 K to 273 K) to elucidate its behavior on the surface of Mars. A Raman microscope equipped with an environmental cell was used to simulate Mars relevant temperature and relative humidity conditions and monitor deliquescence (solid to aqueous) and efflorescence (aqueous to solid) phase transitions of Ca(ClO4)2. Deliquescence and efflorescence were monitored visually using optical images and spectroscopically using Raman microscopy. We find that there is a wide range of deliquescence RH values between 5% and 55% RH. This range is due to the formation of hydrates in different temperatures regimes, with the higher DRH values occurring at the lowest temperatures. Experimental deliquescence results were compared to a thermodynamic model for three hydration states of Ca(ClO4)2. The model predicts that the higher hydration states deliquesce at a higher RH than the lower hydration states. Calcium perchlorate was found to supersaturate, with lower ERH values than DRH values. The ERH results were less dependent on temperature with an average 15 ±± 4%, but values as low as 3 ±± 2% were measured at 273 K. Levitation experiments were performed on single particles of Ca(ClO4)2 and Mg(ClO4)2 at 298 K. While efflorescence was observed around 15% RH for Mg(ClO4)2, the efflorescence of Ca(ClO4)2 was not observed, even when exposed to 1% RH at 298 K. Additionally, a 17-hour experiment was conducted to simulate a martian subsurface diurnal cycle. This demonstrated Ca(ClO4)2 aqueous solutions can persist without efflorescing for the majority of a martian sol, up to 17 hours under Mars temperature heating rates and RH conditions. We find that Ca(ClO4)2 aqueous solutions could persist for most of the martian sol under present-day conditions. The aqueous phase stability and metastability quantified for Ca(ClO4)2 under Mars relevant temperature and relative humidity conditions has important implications for the water cycle and the stability of liquid water on present day Mars.

Reference
Nuding DL, Rivera-Valentin EG, Davis RD, Gough RV, Chevrier VF, Tolbert MA (2014) Deliquescence and Efflorescence of Calcium Perchlorate: An Investigation of Stable Aqueous Solutions Relevant to Mars. Icarus (in Press)
Link to Article [DOI: 10.1016/j.icarus.2014.08.036]

Copyright Elsevier

¹S. Schröder et al. (>10)*
¹Institut de Recherche en Astrophysique et Planétologie (IRAP), CNRS/Université de Toulouse, UPS-OMP, BP 44346, 31028 Toulouse, France
*Find the extensive, full author and affiliation list on the publishers Website

One of the main advantages of ChemCam’s LIBS (Laser-Induced Breakdown Spectroscopy) instrument onboard the Curiosity rover is its potential to detect light elements such as hydrogen at fine scales, which has never been achieved on Mars. Hydrogen lines are detected in most of the data obtained within the first 320 sols of the mission at Gale Crater, Mars. This work is a description of the hydrogen signal and its variability in the ChemCam LIBS spectra; it discusses the challenges of qualitative and quantitative analysis. Data acquisition and processing steps are investigated and optimized for the detection of hydrogen on Mars. Subtraction of an appropriate dark spectrum and the deconvolution of the superimposed emission of carbon from the low-pressure CO2-dominated atmosphere are particularly important. Because the intensities of hydrogen are also affected by matrix effects, the hydrogen signal was investigated within groups of targets sharing common chemical features and similar matrices. The different groups cover a variety of rock and soil compositions encountered along the traverse (calcium sulfate veins, mafic soils, felsic, Mg-rich and Fe-rich rocks) including data from both drill holes and their tailings. Almost all these targets were found to be hydrated to variable extents. Soils have systematically higher hydrogen signals than rocks and pebbles, probably as a result of their alteration. The results from rocks suggest that various alteration processes leading to their hydration have taken place, which is consistent with the fluvial lacustrine context, the diagenetic features, and the mineralogy observed by Curiosity in Yellowknife Bay.

Reference
Schröder S et al. (2014) Hydrogen detection with ChemCam at Gale crater. Icarus (in Press)
Link to Article [DOI: 10.1016/j.icarus.2014.08.029]

Copyright Elsevier

¹Masayuki Uesugi et al. (>10)*
¹Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA), 3-1-1 Yoshinodai, Sagamihara, Kanagawa 252-5210, Japan
*Find the extensive, full author and affiliation list on the publishers website

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

Reference
Uesugi M et al. (2014) Sequential analysis of carbonaceous materials in Hayabusa-returned samples for the determination of their origin. Earth, Planets and Space 66:102
Link to Article [doi:10.1186/1880-5981-66-102]