2019/09/30 by Piotr Guzik, Michał Drahus, Krzysztof Rusek +3 · 138 citations
Physics and Astronomy · #Astro and Planetary Science #Astrophysics and Star Formation Studies #Characterization (materials science) #Comet #Formation and evolution of the Solar System #Interstellar comet #Interstellar medium #Nuclear physics research studies #Orbit (dynamics) #Solar System #Telescope #astro-ph.EP #astro-ph.SR
paper · pdf · doi:10.1038/s41550-019-0931-8
published in Nature Astronomy 4(1), 53-57 (Nature Portfolio) · Published in Nature Astronomy on 14 October 2019
arxiv created 2019/10/14 · openalex publication_date 2019/10/14 · arxiv updated 2019/10/15 · openalex created_date 2019/10/18 · openalex updated_date 2026/08/05
Interstellar comets penetrating through the Solar System had been anticipated for decades. The discovery of asteroidal-looking 'Oumuamua was thus a huge surprise and a puzzle. Furthermore, the physical properties of the 'first scout' turned out to be impossible to reconcile with Solar System objects, challenging our view of interstellar minor bodies. Here, we report the identification and early characterization of a new interstellar object, which has an evidently cometary appearance. The body was discovered by Gennady Borisov on 30 August 2019 UT and subsequently identified as hyperbolic by our data mining code in publicly available astrometric data. The initial orbital solution implies a very high hyperbolic excess speed of ~32 km/s, consistent with 'Oumuamua and theoretical predictions. Images taken on 10 and 13 September 2019 UT with the William Herschel Telescope and Gemini North Telescope show an extended coma and a faint, broad tail. We measure a slightly reddish colour with a g'-r' colour index of 0.66 +/- 0.01 mag, compatible with Solar System comets. The observed morphology is also unremarkable and best explained by dust with a power-law size-distribution index of -3.7 +/- 1.8 and a low ejection speed (44 +/- 14 m/s for β = 1 particles, where β is the ratio of the solar gravitational attraction to the solar radiation pressure). The nucleus is probably ~1 km in radius, again a common value among Solar System comets, and has a negligible chance of experiencing rotational disruption. Based on these early characteristics, and putting its hyperbolic orbit aside, 2I/Borisov appears indistinguishable from the native Solar System comets.