The background temperature of the protoplanetary disk within the first four million years of the Solar System

1Devin L.Schrader, 2Roger R.Fu, 3Steven J.Desch, 1Jemma Davidson
Earth and Planetary Science Letters 504, 30-37 Link to Article [https://doi.org/10.1016/j.epsl.2018.09.030]
1Center for Meteorite Studies, School of Earth and Space Exploration, Arizona State University, 781 East Terrace Road, Tempe, AZ 85287, United States of America
2Department of Earth and Planetary Sciences, Harvard University, 20 Oxford St., Cambridge, MA 02138, United States of America
3School of Earth and Space Exploration, Arizona State University, PO Box 871404, Tempe, AZ 85287, United States of America
Copyright Elsevier

The background temperature of the protoplanetary disk is a fundamental but poorly constrained parameter that strongly influences a wide range of conditions and processes in the early Solar System, including the widespread process(es) by which chondrules originate. Chondrules, mm-scale objects composed primarily of silicate minerals, were formed in the protoplanetary disk almost entirely during the first four million years of Solar System history but their formation mechanism(s) are poorly understood. Here we present new constraints on the sub-silicate solidus cooling rates of chondrules at <873 K (600 °C) using the compositions of sulfide minerals. We show that chondrule cooling rates remained relatively rapid (∼100 to 101 K/hr) between 873 and 503 K, which implies a protoplanetary disk background temperature of <503 K (230 °C) and is consistent with many models of chondrule formation by shocks in the solar nebula, potentially driven by the formation of Jupiter and/or planetary embryos, as the chondrule formation mechanism. This protoplanetary disk background temperature rules out current sheets and resulting short-circuit instabilities as the chondrule formation mechanism. More detailed modeling of chondrule cooling histories in impacts is required to fully evaluate impacts as a chondrule formation model. These results motivate further theoretical work to understand the expected thermal evolution of chondrules at ≤873 K under a variety of chondrule formation scenarios.

Geology of Hebes Chasma, Mars: 1. Structure, stratigraphy, and mineralogy of the interior layered deposits (ILDs)

1Gene Schmidt, 2Frank Fueten, 3Robert Stesky, 4Jessica Flahaut, 5Ernst Hauber
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2018JE005658]
1IRSPS, Universita “G.D’Annunzio”, Pescara, Italy
2Department of Earth Sciences, Brock University, St. Catharines, Ontario, Canada
3Pangaea Scientific, Brockville, Ontario, Canada
4CNRS (institute)/CRPG Nancy (department), France
5Institute of Planetary Research, German Aerospace Center (DLR), Berlin, Germany
Published by arrangement with John Wiley & Sons

Hebes Chasma is an 8 km deep, 126 by 314 km, isolated basin that is partially filled with massive deposits of water‐altered strata called interior layered deposits (ILD). By analyzing the ILD’s structure, stratigraphy and mineralogy, a depositional history of Hebes Chasma is interpreted. Three distinct ILD units were found and are informally referred to as the Lower, Upper and Late ILD. These units are distinguished by their layer thicknesses, layer attitudes, mineralogies and erosional landforms. The Lower and Upper ILDs comprise the chasma’s 7.5 km tall, 120 by 43 km, central mound and the Late ILD is located in the valley between the central mound and the chasma’s northern wall. A horizontal unconformity separates the Lower and Upper ILDs and layer attitudes revealed large‐scale shallow folding within the Lower ILD. All ILDs are characterized by both monohydrated and polyhydrated sulfates (MHS and PHS) signatures. Erosional landforms such as hummocks, polygons, and debris flows suggest past glacial activity within the chasma. A scenario involving several ash fall events during various stages of chasma formation is proposed as the dominant setting throughout Hebes’ geologic history.

Chlorate/Fe‐Bearing Phase Mixtures as a Possible Source of Oxygen and Chlorine Detected by the Sample Analysis at Mars (SAM) Instrument in Gale Crater, Mars

1J. V. Hogancamp, 2B. Sutter, 3R. V. Morris, 2P. D. Archer, 31D. W. Ming, 3E. B. Rampe, 4P. Mahaffy, 5R. Navarro‐Gonzalez
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2018JE005691]
1Geocontrols Systems–Jacobs JETS Contract, NASA Johnson Space Center, Houston, TX, USA
2Jacobs, NASA Johnson Space Center, Houston, TX, USA
3NASA Johnson Space Center, Houston, TX, USA
4NASA Goddard Space Flight Center, Greenbelt, MD, USA
5Universidad Nacional Autonoma de Mexico, Mexico
Published by arrangement with John Wiley & Sons

Oxygen and HCl gas releases detected by the Sample Analysis at Mars (SAM) instrument on board the Mars Science Laboratory Curiosity rover in several Gale Crater samples have been attributed to the thermal decomposition of perchlorates and/or chlorates. Previous experimental studies of perchlorates mixed with Fe‐bearing phases explained some but not all of the evolved oxygen releases, and cannot explain the HCl releases. The objective of this paper was to evaluate the oxygen and HCl releases of chlorates and chlorate/Fe‐phase mixtures in experimental studies and SAM evolved gas analysis (EGA) datasets. Potassium, magnesium, and sodium chlorate were independently mixed with hematite, magnetite, ferrihydrite, and palagonite and analyzed in a thermal evolved gas analyzer configured to operate similarly to the SAM instrument. Fe‐phases depressed the chlorate decomposition temperature 3‐214 °C and consumed up to 75% of the evolved oxygen from chlorate decomposition. Chlorate/Fe‐phase mixtures have oxygen and HCl releases consistent with some samples analyzed by SAM. Reported oxychlorine abundances based on calculations using oxygen detected by SAM could be minimum values because Fe‐phases consume evolved oxygen. The results of this work demonstrate that chlorates could be present in the Martian soil and that oxygen and HCl release temperatures could be used to constrain which chlorate cation species are present in samples analyzed by SAM. Knowledge of which chlorates may be present in Gale Crater creates a better understanding of the detectability of organics by evolved gas analysis, habitability potential, and the chlorine cycle on Mars.

Lunar surface processes inferred from cosmogenic radionuclides in Apollo 16 double drive core 68002/68001

1Steven A.Binnie, 1Kunihiko Nishiizumi, 1Kees C.Welten, 2,3Marc W.Caffee, 4Dirk Hoffmeister
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2018.09.036]
1Space Sciences Laboratory, University of California, Berkeley, 7 Gauss Way, Berkeley, CA 94720-7450, USA
2Department of Physics and Astronomy, Purdue University, West Lafayette, IN 47907-1306, USA
3Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN 47907-1306, USA
4Institute for Geography, University of Cologne, Otto-Fischer-Str. 4, 50674, Cologne, Germany
Copyright Elsevier

Measurements of cosmogenic 10Be, 26Al and 36Cl in Apollo 16 double drive core 68002/68001 are combined with a high resolution digital surface model of the sampling site to investigate the surface processes on the Moon. We find both a significant deficit of solar cosmic ray (SCR)-produced 26Al and a lack of SCR-produced 36Cl in the top 3-5 g/cm2 of the lunar regolith. The topographic model shows the core was taken from just inside a crater with a rim diameter of 25-30 cm. These observations are consistent with regolith removal and displacement by a shallow impact that occurred on the order of 100 kyr ago, or less. Our findings are also compatible with shallow mixing, or gardening, of the lunar regolith to depths of a few cm, a value often found in other lunar cores over the ∼106 yr averaging times of 26Al and 53Mn measurements. More definitive regolith mixing depth estimates are not possible due to the likelihood of disturbance in the top of the core as a result of sampling and/or handling. Our results support the hypothesis that the lunar surface experiences more frequent disturbances by small primary and secondary impacts than has previously been assumed. Additionally, we find no evidence that fine-grained ejecta from the 2.0 Myr old South Ray Crater impact reached this site. If the layer of fine-grained ejecta that reached the sampling site from the South Ray Crater was no more than a few cm thick, this absence can be explained by the erosion that formed the small, relatively recent crater at the coring location.

Thermal radiation from impact plumes

1Vladimir Svetsov, 1Valery Shuvalov
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13200]
1Institute for Dynamics of Geospheres, Russian Academy of Sciences, Moscow, Russia
Published by arrangement with John Wiley & Sons

Plumes produced by the impacts of asteroids and comets consist of rock vapor and heated air. They emit visible light, ultraviolet, and infrared radiation, which can greatly affect the environment. We have carried out numerical simulations of the impacts of stony and cometary bodies with a diameter of 0.3, 1, and 3 km, which enter the atmosphere at various angles, using a hydrodynamic model supplemented by radiation transfer. We assumed that the cosmic object has no strength, and deforms, fragments, and vaporizes in the atmosphere. After the impact on the ground, the formation of craters and plumes was simulated, taking the internal friction of destroyed rocks and the trail formed in the atmosphere into account. The equation of radiative transfer, added to the equations of gas dynamics, was used in the approximation of radiative heat conduction or, if the Rosseland optical depth of a radiating volume of gas and vapor was less than unity, in the volume‐emission approximation. We used temperature and density distributions obtained in these simulations to calculate radiation fluxes on the Earth’s surface by integrating the equation of radiative transfer along rays passing through a luminous region. We used tables of the equation of state of dunite and quartz (for stony impactors and a target) and air, as well as tables of absorption coefficients of air, vapor of ordinary chondrite, and vapor of cometary material. We have calculated the radiation impulse on the ground and the impact radiation efficiency (a ratio of thermal radiation energy incident on the ground to the kinetic energy of a body), which ranges from ~0.5% to ~9%, depending on the impactor size and the angle of entry into the atmosphere. Direct thermal radiation from fireballs and impact plumes, poses a great danger to people, animals, plants, and economic objects. After the impacts of asteroids at a speed of 20 km s−1 at an angle of 45°, a fire can occur at a distance of 250 km if the asteroid has a diameter of 0.3 km, and at a distance of 2000 km if the diameter is 3 km.

Cooling rates of lunar orange glass beads

1Hejiu Hui(惠鹤九), 2Kai-Uwe Hess, 3Youxue Zhang(张有学), 4Alexander R.L.Nichols, 5Anne H.Peslier, 3Rebecca A.Lange, 2Donald B.Dingwell, 6Clive R.Neal
Earth and Planetary Science Letters 503, 88-94 Link to Article [https://doi.org/10.1016/j.epsl.2018.09.019]
1State Key Laboratory for Mineral Deposits Research & Lunar and Planetary Science Institute, School of Earth Sciences and Engineering, Nanjing University, Nanjing, Jiangsu 210023, China
2Department of Earth and Environmental Sciences, LMU-University of Munich, Theresienstrasse 41/III, 80333 Munich, Germany
3Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, MI 48109, USA
4Department of Geological Sciences, University of Canterbury, Christchurch 8140, New Zealand
5Jacobs, NASA-Johnson Space Center, Mail Code X13, Houston, TX 77058, USA
6Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, Notre Dame, IN 46556, USA
Copyright Elsevier

It is widely accepted that the Apollo 17 orange glass beads are of volcanic origin. The degree of degassing of the glass beads depends on their cooling rates, so the estimation of volatile contents in the parental magmas of these lunar pyroclastic glasses also depends on the cooling rates. The cooling rate can be estimated using the calorimetric properties of the glass across the glass transition. In this study, a series of heat capacity measurements were carried out on hand-picked lunar volcanic orange glass beads during several cycles of heating to temperatures above their glass transition using a differential scanning calorimeter. The cooling rate of orange glass beads (sample 74220,867) was calculated to be 101 K/min using the correlation between glass cooling rates and fictive temperatures estimated from their heat capacity–temperature paths. This cooling rate is close to the lower end of the range that best fits the diffusion profiles of several volatile species in the glass beads, and at the upper end of the cooling-rate range recorded in glasses quenched subaerially on Earth. The cooling rate is likely to be controlled by the cooling environment (cooling medium) such that the lunar volcanic glass beads could have been cooled in a gaseous medium released from volcanic eruptions on the Moon, but not during “free flight” in vacuum. The existence of a gas medium suggests, in turn, that there may have been at least a short-lived or episodic atmosphere on the early Moon at around 3.5 Ga.