N. G. RUDRASWAMI¹, D. FERNANDES¹, Agnelo DE ARAUJO¹, M. SHYAM PRASAD¹,and S. TAYLOR²
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13105]
¹National Institute of Oceanography (Council of Scientific and Industrial Research), Dona Paula, Goa 403004, India
²Cold Regions Research and Engineering Laboratory, 72 Lyme Road, Hanover, New Hampshire 03755–1290, USA
Published by arrangement with John Wiley & Sons

We studied 149 pyroxenes from 69 pyroxene‐bearing micrometeorites collected from deep‐sea sediments of the Indian Ocean and South Pole Water Well at Antarctica, Amundsen‐Scott South Pole station. The minor elements in pyroxenes from micrometeorites are present in the ranges as follows: MnO ~0.0–0.4 wt%, Al₂O₃ ~0.0–1.5 wt%, CaO ~0.0–1.0 wt%, Cr₂O₃ ~0.3–0.9 wt%, and FeO ~0.5–4 wt%. Their chemical compositions suggest that pyroxene‐bearing micrometeorites are mostly related to precursors from carbonaceous chondrites rather than ordinary chondrites. The Fe/(Fe+Mg) ratio of the pyroxenes and olivines in micrometeorites shows similarities to carbonaceous chondrites with values lying between 0 and 0.2, and those with values beyond this range are dominated by ordinary chondrites. Atmospheric entry of the pyroxene‐bearing micrometeorites is expected to have a relatively low entry velocity of <16 km s⁻¹ and high zenith angle (70–90°) to preserve their chemical compositions. In addition, similarities in the pyroxene and olivine mineralogical compositions between carbonaceous chondrites and cometary particles suggest that dust in the solar system is populated by materials from different sources that are chemically similar to each other. Our results on pyroxene chemical compositions reveal significant differences with those from ordinary chondrites. The narrow range in olivine and pyroxene chemical compositions are similar to those from carbonaceous chondrites, and a small proportion to ordinary chondrites indicates that dust is largely sourced from carbonaceous chondrite‐type bodies.

Xiao Hu (胡晓)^1,2, Jonathan C. Tan^1,3, Zhaohuan Zhu (朱照寰)², Sourav Chatterjee⁴, Tilman Birnstiel⁵, Andrew N. Youdin⁶, and Subhanjoy Mohanty⁷

Astrophysical Journal 857, 20 Link to Article [DOI: 10.3847/1538-4357/aaad08]
¹Department of Astronomy, University of Florida, Gainesville, FL 32611, USA
²Department of Physics and Astronomy, University of Nevada, Las Vegas, 4505 South Maryland Parkway, Las Vegas, NV 89154, USA
³Department of Physics, University of Florida, Gainesville, FL 32611, USA
⁴Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA), Physics and Astronomy, Northwestern University, Evanston, IL 60208, USA
⁵University Observatory, Faculty of Physics, Ludwig-Maximilians-Universität München, Scheinerstr. 1, D-81679 Munich, Germany
⁶Department of Astronomy and Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA
⁷Imperial College London, 1010 Blackett Lab, Prince Consort Rd., London SW7 2AZ, UK

Systems with tightly packed inner planets (STIPs) are very common. Chatterjee & Tan proposed Inside-out Planet Formation (IOPF), an in situ formation theory, to explain these planets. IOPF involves sequential planet formation from pebble-rich rings that are fed from the outer disk and trapped at the pressure maximum associated with the dead zone inner boundary (DZIB). Planet masses are set by their ability to open a gap and cause the DZIB to retreat outwards. We present models for the disk density and temperature structures that are relevant to the conditions of IOPF. For a wide range of DZIB conditions, we evaluate the gap-opening masses of planets in these disks that are expected to lead to the truncation of pebble accretion onto the forming planet. We then consider the evolution of dust and pebbles in the disk, estimating that pebbles typically grow to sizes of a few centimeters during their radial drift from several tens of astronomical units to the inner, 1 au scale disk. A large fraction of the accretion flux of solids is expected to be in such pebbles. This allows us to estimate the timescales for individual planet formation and the entire planetary system formation in the IOPF scenario. We find that to produce realistic STIPs within reasonable timescales similar to disk lifetimes requires disk accretion rates of ~10⁻⁹ M _⊙ yr⁻¹ and relatively low viscosity conditions in the DZIB region, i.e., a Shakura–Sunyaev parameter of α ~ 10⁻⁴.