Hiroshi Hidaka¹ and Shigekazu Yoneda²

¹Department of Earth and Planetary Systems Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan
²Department of Science and Engineering, National Museum of Nature and Science, Tsukuba 305-0005, Japan

The idea that solar system materials were irradiated by solar cosmic rays from the early Sun has long been suggested, but is still questionable. In this study, Sr, Ba, Ce, Nd, Sm, and Gd isotopic compositions of sequential acid leachates from the Kapoeta meteorite (howardite) were determined to find systematic and correlated variations in their isotopic abundances of proton-rich nuclei, leading to an understanding of the irradiation condition by cosmic rays. Significantly large excesses of proton-rich isotopes (p-isotopes), ⁸⁴Sr,¹³⁰Ba, ¹³²Ba, ¹³⁶Ce, ¹³⁸Ce, and ¹⁴⁴Sm, were observed, particularly in the first chemical separate, which possibly leached out of the very shallow layer within a few ?m from the surface of regolith grains in the sample. The results reveal the production of p-isotopes through the interaction of solar cosmic rays with the superficial region of the regolith grains before the formation of the Kapoeta meteorite parent body, suggesting strong activity in the early Sun

Reference
Hidaka H and Yoneda S (2014) Isotopic Excesses of Proton-rich Nuclei Related to Space Weathering Observed in a Gas-rich Meteorite Kapoeta. The Astrophysical Journal 786:138.
[doi:10.1088/0004-637X/786/2/138]

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Silvia Protopapa^a et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

^aDepartment of Astronomy, University of Maryland, College Park, MD, 20742, USA

On November 4th, 2010, the Deep Impact eXtended Investigation (DIXI) successfully encountered comet 103P/Hartley 2, when it was at a heliocentric distance of 1.06 AU. Spatially resolved near-IR spectra of comet Hartley 2 were acquired in the 1.05 – 4.83 μm wavelength range using the HRI-IR spectrometer. We present spectral maps of the inner ∼10 kilometers of the coma collected 7 minutes and 23 minutes after closest approach. The extracted reflectance spectra include well-defined absorption bands near 1.5, 2.0, and 3.0 μm consistent in position, bandwidth, and shape with the presence of water ice grains. Using Hapke’s radiative transfer model, we characterize the type of mixing (areal vs. intimate), relative abundance, grain size, and spatial distribution of water ice and refractories. Our modeling suggests that the dust, which dominates the innermost coma of Hartley 2 and is at a temperature of 300K, is thermally and physically decoupled from the fine-grained water ice particles, which are on the order of 1 μm in size. The strong correlation between the water ice, dust, and CO₂ spatial distribution supports the concept that CO₂ gas drags the water ice and dust grains from the nucleus. Once in the coma, the water ice begins subliming while the dust is in a constant outflow. The derived water ice scale-length is compatible with the lifetimes expected for 1-μm pure water ice grains at 1 AU, if velocities are near 0.5 m/s. Such velocities, about three order of magnitudes lower than the expansion velocities expected for isolated 1-μm water ice particles ( and ), suggest that the observed water ice grains are likely aggregates.

Reference
Protopapa S (in press) Water ice and dust in the innermost coma of Comet 103P/Hartley 2. Icarus
[doi:10.1016/j.icarus.2014.04.008]
Copyright Elsevier

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