Unusual polarimetric properties for interstellar comet 2I/Borisov

S. Bagnulo , A. Cellino , L. Kolokolova , R. Nežič , T. Santana-Ros , G. Borisov , A. Christou , Ph. Bendjoya (1) , M. Devogèle

1 LAGRANGE - Joseph Louis LAGRANGE

Abstract So far, only two interstellar objects have been observed within our Solar System. While the first one, 1I/‘Oumuamua, had asteroidal characteristics, the second one, 2I/Borisov, showed clear evidence of cometary activity. We performed polarimetric observations of comet 2I/Borisov using the European Southern Observatory Very Large Telescope to derive the physical characteristics of its coma dust particles. Here we show that the polarization of 2I/Borisov is higher than what is typically measured for Solar System comets. This feature distinguishes 2I/Borisov from dynamically evolved objects such as Jupiter-family and all short- and long-period comets in our Solar System. The only object with similar polarimetric properties as 2I/Borisov is comet C/1995 O1 (Hale-Bopp), an object that is believed to have approached the Sun only once before its apparition in 1997. Unlike Hale-Bopp and many other comets, though, comet 2I/Borisov shows a polarimetrically homogeneous coma, suggesting that it is an even more pristine object.

Domaines: Planétologie et astrophysique de la terre [astro-ph.EP]

S. Bagnulo, A. Cellino, L. Kolokolova, R. Nežič, T. Santana-Ros, et al.. Unusual polarimetric properties for interstellar comet 2I/Borisov. Nature Communications, 2021, 12 (1), ⟨10.1038/s41467-021-22000-x⟩. ⟨hal-03472673⟩