Significantly high polarization degree of the very low-albedo asteroid (152679) 1998 KU$_\mathrm{2}$

Daisuke Kuroda; Masateru Ishiguro; Makoto Watanabe; Sunao Hasegawa; Tomohiko Sekiguchi; Hiroyuki Naito; Fumihiko Usui; Masataka Imai; Mitsuteru Sato; Kiyoshi Kuramoto

doi:10.1051/0004-6361/201732086

arXiv · 1712.01444

Significantly high polarization degree of the very low-albedo asteroid (152679) 1998 KU$_\mathrm{2}$

Daisuke Kuroda·Masateru Ishiguro·Makoto Watanabe·Sunao Hasegawa·Tomohiko Sekiguchi·Hiroyuki Naito·Fumihiko Usui·Masataka Imai·Mitsuteru Sato·Kiyoshi Kuramoto

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Abstract

We present a unique and significant polarimetric result regarding the near-Earth asteroid (152679) 1998 KU$_\mathrm{2}$ , which has a very low geometric albedo. From our observations, we find that the linear polarization degrees of 1998 KU$_\mathrm{2}$ are 44.6 $\pm$ 0.5\% in the R$_\mathrm{C}$ band and 44.0 $\pm$ 0.6\% in the V band at a solar phase angle of 81.0\degr. These values are the highest of any known airless body in the solar system (i.e., high-polarization comets, asteroids, and planetary satellites) at similar phase angles. This polarimetric observation is not only the first for primitive asteroids at large phase angles, but also for low-albedo (< 0.1) airless bodies. Based on spectroscopic similarities and polarimetric measurements of materials that have been sorted by size in previous studies, we conjecture that 1998 KU$_\mathrm{2}$ has a highly microporous regolith structure comprising nano-sized carbon grains on the surface.

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Daisuke Kuroda, Masateru Ishiguro, Makoto Watanabe, Sunao Hasegawa, Tomohiko Sekiguchi, Hiroyuki Naito, Fumihiko Usui, Masataka Imai, Mitsuteru Sato, Kiyoshi Kuramoto. 2017-12-05. Significantly high polarization degree of the very low-albedo asteroid (152679) 1998 KU$_\mathrm{2}$. https://doi.org/10.1051/0004-6361%2F201732086

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