Derek W. Sears¹ and Robert Beauford²

¹Bay Area Environmental Research Institute/NASA Ames Research Center, Mountain View, California, USA
²Arkansas Center for Space and Planetary Sciences, University of Arkansas, Fayetteville, Arkansas, USA

A piece of the Sutter’s Mill meteorite, fragment SM2-1d, has been examined using thermoluminescence techniques to better understand its thermal and metamorphic history. The sample had very weak but easily measureable natural and induced thermoluminescence (TL) signals; the signal-to-noise ratio was better than 10. The natural TL was restricted to the high-temperature regions of the glow curve suggesting that the meteorite had been heated to approximately 300 °C within the time it takes for the TL signal to recover from a heating event, probably within the last 10⁵ years. It is possible that this reflects heating during release from the parent body, close passage by the Sun, or heating during atmospheric passage. Of these three options, the least likely is the first, but the other possibilities are equally likely. It seems that temperatures of approximately 300 °C reached 5 or 6 mm into the meteorite, so that all but one of the small Sutter’s Mill stones have been heated. The Dhajala normalized induced TL signal for SM2-1d is comparable to that of type 3.0 chondrites and is unlike normal CM chondrites, the class it most closely resembles, which do not have detectable TL sensitivity. The shape of the induced TL curve is comparable to other low-type ordinary, CV, and CO chondrites, in that it has a broad hummocky structure, but does not resemble any of them in detail. This suggests that Sutter’s Mill is a unique, low-petrographic–type (3.0) chondrite.

Reference
Sears DW and Beauford R (in press) The Sutter’s Mill meteorite: Thermoluminescence data on thermal and metamorphic history. Meteoritics & Planetary Science
[doi:10.1111/maps.12259]
Published by arrangement with John Wiley & Sons

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Anthony L. Piro¹ and Ehud Nakar²

¹Theoretical Astrophysics, California Institute of Technology, 1200 E California Boulevard, M/C 350-17, Pasadena, CA 91125, USA
²Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978, Israel

Ongoing transient surveys are presenting an unprecedented account of the rising light curves of Type Ia supernovae (SNe Ia). This early emission probes the shallowest layers of the exploding white dwarf (WD), which can provide constraints on the progenitor star and the properties of the explosive burning. We use semianalytic models of radioactively powered rising light curves to analyze these observations. As we have summarized in previous work, the main limiting factor in determining the surface distribution of ⁵⁶Ni is the lack of an unambiguously identified time of explosion, as would be provided by detection of shock breakout or shock-heated cooling. Without this the SN may in principle exhibit a “dark phase” for a few hours to days, where the only emission is from shock-heated cooling that is too dim to be detected. We show that by assuming a theoretically motivated time-dependent velocity evolution, the explosion time can be better constrained, albeit with potential systematic uncertainties. This technique is used to infer the surface ⁵⁶Ni distributions of three recent SNe Ia that were caught especially early in their rise. In all three we find fairly similar ⁵⁶Ni distributions. Observations of SN 2011fe and SN 2012cg probe shallower depths than SN 2009ig, and in these two cases ⁵⁶Ni is present merely ~10^-2 M_☉ from the WDs’ surfaces. The uncertainty in this result is up to an order of magnitude given the difficulty of precisely constraining the explosion time. We also use our conclusions about the explosion times to reassess radius constraints for the progenitor of SN 2011fe, as well as discuss the roughly t 2 power law that is inferred for many observed rising light curves.

Reference
Piro AL and Nakar E (2014) Constraints on Shallow 56Ni from the Early Light Curves of Type Ia Supernovae. The Astrophysical Journal 784:85
[doi:10.1088/0004-637X/784/1/85]

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Fred J. Ciesla

Department of the Geophysical Sciences, The University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637, USA

Understanding the phases of water ice that were present in the solar nebula has implications for understanding cometary and planetary compositions as well as the internal evolution of these bodies. Here we show that amorphous ice formed more readily than previously recognized, with formation at temperatures <70 K being possible under protoplanetary disk conditions. We further argue that photodesorption and freeze-out of water molecules near the surface layers of the solar nebula would have provided the conditions needed for amorphous ice to form. This processing would be a natural consequence of ice dynamics and would allow for the trapping of noble gases and other volatiles in water ice in the outer solar nebula.

Reference
Ciesla FJ (2014) The Phases of Water Ice in the Solar Nebula. The Astrophysical Journal Letters 784:L1
[doi:10.1088/2041-8205/784/1/L1]

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David Jewitt^1,2, Jessica Agarwal³, Jing Li³, Harold Weaver⁴, Max Mutchler⁵, and Stephen Larson⁶

¹Department of Earth, Planetary and Space Sciences, UCLA, 595 Charles Young Drive East, Los Angeles, CA 90095-1567, USA
²Department of Physics and Astronomy, University of California at Los Angeles, 430 Portola Plaza, Box 951547, Los Angeles, CA 90095-1547, USA
³Max Planck Institute for Solar System Research, Max-Planck-Str. 2, D-37191 Katlenburg-Lindau, Germany
⁴The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, USA
⁵Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
⁶Lunar and Planetary Laboratory, University of Arizona, 1629 E. University Boulevard, Tucson, AZ 85721-0092, USA

Splitting of the nuclei of comets into multiple components has been frequently observed but, to date, no main-belt asteroid has been observed to break up. Using the Hubble Space Telescope, we find that main-belt asteroid P/2013 R3 consists of 10 or more distinct components, the largest up to 200 m in radius (assumed geometric albedo of 0.05) each of which produces a coma and comet-like dust tail. A diffuse debris cloud with total mass ~2 × 10⁸ kg further envelopes the entire system. The velocity dispersion among the components, ΔV ~ 0.2-0.5 m s^–1, is comparable to the gravitational escape speeds of the largest members, while their extrapolated plane-of-sky motions suggest a break up between 2013 February and September. The broadband optical colors are those of a C-type asteroid. We find no spectral evidence for gaseous emission, placing model-dependent upper limits to the water production rate ≤1 kg s^–1. Breakup may be due to a rotationally induced structural failure of the precursor body.

Reference
Jewitt D, Agarwal J, Li J, Weaver H, Mutchler M and Larson S (2014) Disintegrating Asteroid P/2013 R3. The Astrophysical Journal Letters 784:L8
[doi:10.1088/2041-8205/784/1/L8]

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