¹James F. J. Bryson, ¹Claire I. O. Nichols,^2,3Julia Herrero-Albillos,⁴Florian Kronast,⁵Takeshi Kasama,⁵Hossein Alimadadi,⁶Gerrit van der Laan,⁷Francis Nimmo¹Richard J. Harrison
¹Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK
²Centro Universitario de la Defensa, Carretera de Huesca s/n, E-50090 Zaragoza, Spain
³Instituto de Ciencia de Materiales de Aragón, CSIC—Universidad de Zaragoza, Pedro Cerbuna 12, E-50009 Zaragoza, Spain
⁴Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Strasse 15, 12489 Berlin, Germany
⁵Center for Electron Nanoscopy, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark
⁶Diamond Light Source, Chilton, Didcot, Oxfordshire OX11 0DE, UK
⁷Department of Earth and Planetary Sciences, University of California, Santa Cruz, California 95064, USA

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Bryson JFJ, Nichols CIO, Herrero-Albillos J, Kronast F, Kasama T, Alimadadi H, van der Laan G, Nimmo F, Harrison RJ (2015) Long-lived magnetism from solidification-driven convection on the pallasite parent Body. Nature 517, 472–475
Link to Article [doi:10.1038/nature14114]

¹M. Millot et al. (>10)*
¹Lawrence Livermore National Laboratory, Livermore, CA 94550, USA.
*Find the extensive, full author and affiliation list on the publishers Website

Deep inside planets, extreme density, pressure, and temperature strongly modify the properties of the constituent materials. In particular, how much heat solids can sustain before melting under pressure is key to determining a planet’s internal structure and evolution. We report laser-driven shock experiments on fused silica, α-quartz, and stishovite yielding equation-of-state and electronic conductivity data at unprecedented conditions and showing that the melting temperature of SiO2 rises to 8300 K at a pressure of 500 gigapascals, comparable to the core-mantle boundary conditions for a 5–Earth mass super-Earth. We show that mantle silicates and core metal have comparable melting temperatures above 500 to 700 gigapascals, which could favor long-lived magma oceans for large terrestrial planets with implications for planetary magnetic-field generation in silicate magma layers deep inside such planets.

Reference
Millot M (2015) Shock compression of stishovite and melting of silica at planetary interior conditions. Science 347, 6220, 418-420
Link to Article [DOI: 10.1126/science.1261507]

Published with permission from AAAS

¹P. R. Mahaffy et al. (>10)*
¹Planetary Environments Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA.
*Find the extensive, full author and affiliation list on the publishers Website

The deuterium-to-hydrogen (D/H) ratio in strongly bound water or hydroxyl groups in ancient martian clays retains the imprint of the water of formation of these minerals. Curiosity’s Sample Analysis at Mars (SAM) experiment measured thermally evolved water and hydrogen gas released between 550° and 950°C from samples of Hesperian-era Gale crater smectite to determine this isotope ratio. The D/H value is 3.0 (±0.2) times the ratio in standard mean ocean water. The D/H ratio in this ~3-billion-year-old mudstone, which is half that of the present martian atmosphere but substantially higher than that expected in very early Mars, indicates an extended history of hydrogen escape and desiccation of the planet.

Reference
Mahaffy PR et al. (2015) The imprint of atmospheric evolution in the D/H of Hesperian clay minerals on Mars.
Science 347, 6220, 412-414
Link to Article [DOI: 10.1126/science.1260291]

Reprinted with permission from AAAS

¹Alessandra Rotundi et al. (>10)*
¹Istituto di Astrofisica e Planetologia Spaziali, Istituto Nazionale di Astrofisica (INAF), Via Fosso del Cavaliere, 100, 0133 Rome, Italy.
*Find the extensive, full author and affiliation list on the publishers website

Critical measurements for understanding accretion and the dust/gas ratio in the solar nebula, where planets were forming 4.5 billion years ago, are being obtained by the GIADA (Grain Impact Analyser and Dust Accumulator) experiment on the European Space Agency’s Rosetta spacecraft orbiting comet 67P/Churyumov-Gerasimenko. Between 3.6 and 3.4 astronomical units inbound, GIADA and OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) detected 35 outflowing grains of mass 10−10 to 10−7 kilograms, and 48 grains of mass 10−5 to 10−2 kilograms, respectively. Combined with gas data from the MIRO (Microwave Instrument for the Rosetta Orbiter) and ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) instruments, we find a dust/gas mass ratio of 4 ± 2 averaged over the sunlit nucleus surface. A cloud of larger grains also encircles the nucleus in bound orbits from the previous perihelion. The largest orbiting clumps are meter-sized, confirming the dust/gas ratio of 3 inferred at perihelion from models of dust comae and trails.

Reference
Rotundi A. et al. (2015) Dust measurements in the coma of comet 67P/Churyumov-Gerasimenko inbound to the Sun. Science 347, 6220
Link to Article [DOI: 10.1126/science.aaa3905]
Printed with permission from AAAS

¹F. Capaccioni et al. (>10)*
¹Istituto di Astrofisica e Planetologia Spaziali, Istituto Nazionale di Astrofisica (INAF), Rome, Italy.
*Find the extensive, full author and affiliation list on the publishers Website

The VIRTIS (Visible, Infrared and Thermal Imaging Spectrometer) instrument on board the Rosetta spacecraft has provided evidence of carbon-bearing compounds on the nucleus of the comet 67P/Churyumov-Gerasimenko. The very low reflectance of the nucleus (normal albedo of 0.060 ± 0.003 at 0.55 micrometers), the spectral slopes in visible and infrared ranges (5 to 25 and 1.5 to 5% kÅ−1), and the broad absorption feature in the 2.9-to-3.6–micrometer range present across the entire illuminated surface are compatible with opaque minerals associated with nonvolatile organic macromolecular materials: a complex mixture of various types of carbon-hydrogen and/or oxygen-hydrogen chemical groups, with little contribution of nitrogen-hydrogen groups. In active areas, the changes in spectral slope and absorption feature width may suggest small amounts of water-ice. However, no ice-rich patches are observed, indicating a generally dehydrated nature for the surface currently illuminated by the Sun.

Reference
Capaccioni F. et al. (2015) The organic-rich surface of comet 67P/Churyumov-Gerasimenko as seen by VIRTIS/Rosetta. Science 347, 6220
Link to Article [DOI: 10.1126/science.aaa0628]

Reprinted with permission of AAAS