¹Stefan Loehle, ^2,3Peter Jenniskens, ⁴Hannah Böhrk, ⁵Thomas Bauer, ⁴Henning Elsäβer, ³Derek W. Sears, ⁶Michael E. Zolensky, ⁷Muawia H. Shaddad
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12788]
¹High Enthalpy Flow Diagnostics Group, Institute of Space Systems, 70569 Stuttgart, Germany
²SETI Institute, Carl Sagan Center, Mountain View, California 94043, USA
³NASA Ames Research Center, Mountain View, California 94035, USA
⁴DLR, Institute of Structures and Design, 70569 Stuttgart, Germany
⁵DLR, Institute of Technical Thermodynamics, 51147 Cologne, Germany
⁶ARES, NASA Johnson Space Center, Houston, Texas 77058, USA
⁷Physics Department, University of Khartoum, Khartoum, Sudan
Published by arrangement with John Wiley & Sons

Asteroid 2008 TC3 was characterized in a unique manner prior to impacting Earth’s atmosphere, making its October 7, 2008, impact a suitable field test for or validating the application of high-fidelity re-entry modeling to asteroid entry. The accurate modeling of the behavior of 2008 TC3during its entry in Earth’s atmosphere requires detailed information about the thermophysical properties of the asteroid’s meteoritic materials at temperatures ranging from room temperature up to the point of ablation (T ~ 1400 K). Here, we present measurements of the thermophysical properties up to these temperatures (in a 1 atm. pressure of argon) for two samples of the Almahata Sitta meteorites from asteroid 2008 TC3: a thick flat-faced ureilite suitably shaped for emissivity measurements and a thin flat-faced EL6 enstatite chondrite suitable for diffusivity measurements. Heat capacity was determined from the elemental composition and density from a 3-D laser scan of the sample. We find that the thermal conductivity of the enstatite chondrite material decreases more gradually as a function of temperature than expected, while the emissivity of the ureilitic material decreases at a rate of 9.5 × 10−5 K−1 above 770 K. The entry scenario is the result of the actual flight path being the boundary to the load the meteorite will be affected with when entering. An accurate heat load prediction depends on the thermophysical properties. Finally, based on these data, the breakup can be calculated accurately leading to a risk assessment for ground damage.

^a,bRobert C.J. Steele, ^a,cVeronika S. Heber, ^aKevin D. McKeegan
Geochimica et Cosmochimica Acta (in Press) Link to Article [http://dx.doi.org/10.1016/j.gca.2016.10.046]
^aDept. of Earth, Planetary, and Space Sciences, University of California – Los Angeles, Los Angeles, CA. 90095-1567, USA
^bNow at: Institute of Geochemistry and Petrology, Department of Earth Sciences, ETH Z ürich, Clausiusstrasse 25, 8092 Zürich, Switzerland
^cNow at: Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
Copyright Elsevier

The short-lived radionuclide ⁵³Mn decays to ⁵³CrCr providing a relative chronometer for dating the formation of Mn-rich minerals in meteorites. Secondary ion mass spectrometry (SIMS) has been extensively used for in situ dating of meteoritic olivine and carbonate by the ⁵³Mn–⁵³Cr system, however a significant analytical challenge has been realising accurate measurements of the Mn/Cr ratio in individual minerals of differing chemical compositions. During Secondary ion mass spectrometry (SIMS) analysis, elements are ionised with differing efficiencies and standard materials are required to calibrate measured ion intensities in terms of relative elemental concentrations. The carbonate system presents a particular analytical difficulty since such standards are not naturally available due to low and variable Cr contents. Here, we utilise ion implantation of Cr into carbonate and other phases to accurately determine the relative sensitivity factors of Mn/Cr during Secondary ion mass spectrometry (SIMS) analysis. We find significant variations in Mn/Cr RSF values among different carbonate minerals that depend systematically on chemical composition and we propose an empirical correction scheme that quantitatively yields an accurate RSF for carbonates of diverse chemical compositions. Correction of previous Secondary ion mass spectrometry (SIMS) carbonate data for this strong matrix effect may help to reconcile some outstanding problems regarding the timescales of aqueous alteration processes in carbonaceous chondrites. Mn-Cr ages, revised based our new understanding of the matrix effect, are, in general, earlier than previously thought and the duration of carbonate formation is shorter.