¹Caroline de Beule, ^1,2Joachim Landers, ^1,2Soma Salamon, ^1,2Heiko Wende, ¹Gerhard Wurm
The Astrophysical Journal 837, 59 Link to Article [https://doi.org/10.3847/1538-4357/837/1/59]
¹Faculty of Physics, University of Duisburg-Essen, Lotharstr. 1, D-47057 Duisburg, Germany
²Center for Nanointegration Duisburg-Essen (CENIDE), University of Duisburg-Essen, Carl-Benz-Str. 199, D-47057 Duisburg, Germany

It is an open question how elevated temperatures in the inner parts of protoplanetary disks influence the formation of planetesimals. We approach this problem here by studying the tensile strength of granular beds with dust samples tempered at different temperatures. We find via laboratory experiments that tempering at increasing temperatures is correlated with an increase in cohesive forces. We studied dust samples of palagonite (JSC Mars-1a) which were tempered for up to 200 hr at temperatures between 600 and 1200 K, and measured the relative tensile strengths of highly porous dust layers once the samples cooled to room temperature. Tempering increases the tensile strength from 800 K upwards. This change is accompanied by mineral transformations, the formation of iron oxide crystallites as analyzed by Mössbauer spectroscopy, changes in the number size distribution, and the morphology of the surface visible as cracks in larger grains. These results suggest a difference in the collisional evolution toward larger bodies with increasing temperature as collisional growth is fundamentally based on cohesion. While high temperatures might also increase sticking (not studied here), compositional evolution will already enhance the cohesion and the possibility of growing larger aggregates on the way toward planetesimals. This might lead to a preferred in situ formation of inner planets and explain the observed presence of dense inner planetary systems.

^1,2Julie D. Stopar, ³Bradley L. Jolliff, ¹Emerson J. Speyerer, ¹Erik I. Asphaug, ¹Mark S. Robinson
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2017.05.010]
¹School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA
²Lunar and Planetary Institute, Houston, TX, USA
³Department of Earth and Planetary Sciences, Washington University in St. Louis, MO, USA

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U.Böttger et al. (>10)*
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2017.05.004]
¹Institute of Optical Sensor Systems, German Aerospace Center (DLR), Rutherfordstr. 2, 12489 Berlin, Germany
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¹Hiroki Chihara, ²Chiyoe Koike
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2017.06.003]
¹Department of General Education, Osaka Sangyo University, 3-1-1, Nakagaito, Daito, Osaka 560-0043, Japan
²Department of Science and Engineering, Ritsumeikan University, Japan

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