^1,2Ekaterina Chornaya,¹Alexander M.Zakharenko,³Evgenij Zubko,^1,4Aleksandr Kuchmizhak,¹Kirill S.Golokhvast,^5,6Gorden Videen
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.113907]
¹Far Eastern Federal University, 8 Sukhanova St., Vladivostok 690950, Russia
²Institute of Applied Astronomy of RAS, 10 Kutuzova Emb., Saint-Petersburg 191187, Russia
³Humanitas College, Kyung Hee University, 1732, Deogyeong-daero, Giheung-gu, Yongin-si, Gyeonggi-do 17104, South Korea
⁴Institute of Automation and Control Processes FEB RAS, 5 Radio St., Vladivostok 690041, Russia
⁵Space Science Institute, 4750 Walnut Street, Boulder, Suite 205, CO 80301, USA
⁶Department of Astronomy and Space Science, Kyung Hee University, 1732, Deogyeong-daero, Giheung-gu, Yongin-si, Gyeonggi-do 17104, South Korea
Copyright Elsevier

We experimentally measure the mid-IR spectra of half-millimeter-sized olivine particles with very compact morphology and smooth surfaces. We find that the 10-μm silicate feature is present in these large, irregularly shaped samples having surface roughness that is much smaller than optical wavelengths. Based on Mie theory, which assumes the particles are spherical, this feature should not exist for such large particles. As a consequence, its presence has been taken as an indicator that the particles or grains composing such particles were micron-sized or smaller. The measurement of this feature in real, irregularly shaped particles, suggests that the assumption of sphericity may severely limit our interpretations of remote-sensing data.

¹Pei Ma et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.113901]
¹Planetary Science Institute, School of Earth Sciences, China University of Geosciences, Wuhan, China
Copyright Elsevier

The Chang’E-4 spacecraft successfully landed in Von Kármán crater inside the South Pole-Aitken basin on the lunar far side on January 3, 2019 and the Yutu-2 Rover has performed explorations on the lunar surface for nine lunar days as of September 2019. Our earlier analysis of the visible and near-infrared spectrometer measurements made by the Yutu-2 rover during the first two lunar days shows that the regolith of the landing site may have come from the nearby Finsen crater and is dominated by plagioclase with lesser amount of mafic minerals. During its third lunar day explorations, the Yutu-2 photographed a small piece of lunar rock and measured its reflectance spectra. Compared with the spectra of its surrounding regolith, this rock’s spectra have deeper absorption features, indicating its fresher nature. To obtain the mineralogy of the rock, we compared the rock’s spectra with the spectral library data of NASA’s reflectance experiment laboratory of returned lunar rocks and lunar meteorites. We found that this rock is also plagioclase-rich with a possible plagioclase abundance of 60–80 vol%. A source region analysis using the Moon Mineralogy Mapper’s remote sensing observations indicates this rock was ejected from the Zhinyu crater, about 30 km west of the landing site, rather than directly from the Finsen crater. Numerical simulations of the Zhinyu crater on the impact cratering process and ejecta thickness distribution confirmed our findings and imply that the surficial materials at the CE-4 landing site experienced a complicated evolution rather than simply retaining the pristine or primordial ejecta directly from the Finsen crater.