Yayoi N. Miura¹, Keisuke Nagao² and Makoto Kimura³

¹Earthquake Research Institute, University of Tokyo, Bunkyo-ku, Tokyo, Japan
²Geochemical Research Center, Graduate School of Science, University of Tokyo, Bunkyo-ku, Tokyo, Japan
³Faculty of Science, Ibaraki University, Mito, Ibaraki, Japan

We analyzed noble gases in nine individual chondrules, an assemblage of small chondrules, and four whole-rock samples of the Allende CV3 chondrite. Major elements were also determined for five chondrules. The cosmic ray exposure ages are calculated from cosmogenic ³He to be 5.17 ± 0.38 and 5.15 ± 0.25 Myr for the averages of the chondrules and whole rocks, respectively, showing no significant pre-exposure evidence for the studied chondrules. Large amounts of ³⁶Ar, ^80,82Kr, and ¹²⁸Xe produced by neutron capture are observed in most samples; the abundances of these nuclides are correlated among the samples. The epithermal neutron flux and neutron slowing down density are calculated based on [⁸⁰Kr]_n, from which a sample depth of about 30 cm can be calculated. The measured chondrules contain variable amounts of radiogenic ¹²⁹Xe. The abundance ratios of radiogenic ¹²⁹Xe to neutron capture–produced ¹²⁸Xe are rather constant among the studied chondrules; four chondrules give more precise ratios at the high-temperature fractions, ranging from 1920 ± 80 to 2280 ± 140, which corresponds to a time difference of 3.9 ± 2.4 Myr. It is noticeable that most chondrules also contain ²⁴⁴Pu-derived fission Xe. The average²⁴⁴Pu/²³⁸U ratio for nine chondrules is 0.0069 ± 0.0018, which agrees well with the preferred ratio reported for chondrites.

Reference
Miura YN, Nagao K and Kimura M (in press) Noble gases in individual chondrules of the Allende CV3 chondrite. Meteoritics & Planetary Science
[doi:10.1111/maps.12313]
Published by arrangement with John Wiley & Sons

Link to Article

Masato Kiuchi and Akiko M. Nakamura

Department of Earth and Planetary Sciences, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe, 657-8501,Japan

We obtain an empirical relationship between porosity and the interparticle force of granular media based on measurement data on the ground. We apply the relationship to the condition of the surface of small bodies to estimate the porosity and the particle size of the regolith.

Reference
Kiuchi M and Nakamura AM (in press) Relationship between Regolith Particle Size and Porosity on Small Bodies. Icarus
[doi:10.1016/j.icarus.2014.05.029]
Copyright Elsevier

Link to Article

Andrea Isella¹, Claire J. Chandler¹, John M. Carpenter¹, Laura M. Pérez^2,3 and Luca Ricci¹

³Department of Astronomy, California Institute of Technology, MC 249-17, Pasadena, CA 91125, USA
³National Radio Astronomy Observatory, P.O. Box 0, Socorro, NM 87801, USA
³Jansky Fellow.

We present Karl G. Jansky Very Large Array (VLA) observations of the 7 mm continuum emission from the disk surrounding the young star LkCa 15. The observations achieve an angular resolution of 70 mas and spatially resolve the circumstellar emission on a spatial scale of 9 AU. The continuum emission traces a dusty annulus of 45 AU in radius that is consistent with the dust morphology observed at shorter wavelengths. The VLA observations also reveal a compact source at the center of the disk, possibly due to thermal emission from hot dust or ionized gas located within a few AU from the central star. No emission is observed between the star and the dusty ring and, in particular, at the position of the candidate protoplanet LkCa 15 b. By comparing the observations with theoretical models for circumplanetary disk emission, we find that if LkCa 15 b is a massive planet (>5 M_J ) accreting at a rate greater than 10⁶ M_J  yr^-1, then its circumplanetary disk is less massive than 0.1 M_J , or smaller than 0.4 Hill radii. Similar constraints are derived for any possible circumplanetary disk orbiting within 45 AU from the central star. The mass estimates are uncertain by at least one order of magnitude due to the uncertainties on the mass opacity. Future ALMA observations of this system might be able to detect circumplanetary disks down to a mass of 5 × 10^-4 M_J and as small as 0.2 AU, providing crucial constraints on the presence of giant planets in the act of forming around this young star.

Reference
Isella A, Chandler CJ, Carpenter JM, Pérez LM and Ricci L (in press) Searching for Circumplanetary Disks around LkCa 15. The Astrophysical Journal 788:129.
[doi:10.1088/0004-637X/788/2/129]

Link to Article