¹Lingzhi Sun,¹Paul Lucey,²Casey I.Honniball,¹Macey Sandford,¹Emily S.Costello,¹Liliane Burkhard,³Reilly Brennan,¹Chiara Ferrari-Wong
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114740]
¹Hawai‘i Institute of Geophysics and Planetology, Department of Earth Sciences, University of Hawai‘i at Mānoa, Honolulu, HI 96822, USA
²NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
³Georgia Institute of Technology, Atlanta, GA 30332, USA
Copyright Elsevier

The reflected light from the lunar surface is polarized and contains perpendicular () and parallel () branches. To provide supporting data for the first polarimetric camera (PolCam) on board the Korean Pathfinder lunar orbiter, in this work, we built a polarimeter and measured the polarized spectra for eight Apollo soils that span a wide range in composition and maturity. We found a linear correlation between reflectance R and the difference of perpendicular and parallel branches: , and b’ might be sensitive to the grain size of lunar soils. The regression coefficient b’ can be derived from both positive and negative polarization spectra and has little dependence on wavelength, thus it has great potential in estimating grain size for lunar soils. We also used radiative transfer equations to calculate the real index of optical constants and to reproduce the perpendicular and parallel polarized spectra for the lunar soils. We correlated polarimetry indexes including polarization degree () and the difference of the perpendicular and parallel branches () with the abundances of FeO and TiO2 and soil maturity, and our result indicates that these two polarimetry indexes show dependence on both the compositions and soil maturity.

^1,2Vardan Adibekyan et al. (>10)
Science 374, 330-332 Link to Article [DOI: 10.1126/science.abg8794]
¹Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, Centro de Astrofísica da Universidade do Porto, 4150-762 Porto, Portugal.
²Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, 4169-007 Porto, Portugal.
Reprinted with permission from AAAS

Stars and planets both form by accreting material from a surrounding disk. Because they grow from the same material, theory predicts that there should be a relationship between their compositions. In this study, we search for a compositional link between rocky exoplanets and their host stars. We estimate the iron-mass fraction of rocky exoplanets from their masses and radii and compare it with the compositions of their host stars, which we assume reflect the compositions of the protoplanetary disks. We find a correlation (but not a 1:1 relationship) between these two quantities, with a slope of >4, which we interpret as being attributable to planet formation processes. Super-Earths and super-Mercuries appear to be distinct populations with differing compositions, implying differences in their formation processes.