Interstellar Comet gb00234
ATel #13100; Piotr Guzik (Jagiellonian Univ.), Michal Drahus (Jagiellonian Univ.), Krzysztof Rusek (AGH UST), Waclaw Waniak (Jagiellonian Univ.), Giacomo Cannizzaro (SRON), Ines Pastor Marazuela (Univ. of Amsterdam, ASTRON)
on 11 Sep 2019; 21:16 UT
Credential Certification: Michal Drahus (drahus@oa.uj.edu.pl)
We report the identification of an interstellar minor body in the stream of astrometric positions that are being submitted to the Minor Planet Center. The body labelled gb00234 was initially identified on 8 September 2019 at 04:15 UT by our software "Interstellar Crusher" (custom Python code that operates on Bill Gray's Find Orb), which monitors the Possible Comet Confirmation Page performing a real-time search for hyperbolic orbits among newly discovered minor bodies. Visual inspection of the input data and orbital fits confirmed the identification. The object was discovered by Gennady Borisov (station L51) on 30 August 2019 at 01:03 UT. At the time of writing, 129 astrometric positions obtained over a 12.42-day interval yield the following hyperbolic solution (epoch 2019 Sep. 11.0 TT):
T = 2019 Dec. 9.745968 +/- 0.94 TT
e = 3.1551235 +/- 0.13
q = 1.95954186 +/- 0.035 au
Peri. = 210.22059 +/- 0.90 deg (2000.0)
Node = 307.71365 +/- 0.33 deg (2000.0)
Incl. = 44.49503 +/- 0.34 deg (2000.0)
(mean residual: 0.49 arcsec)
The orbital elements imply a hyperbolic excess speed of 30 km/s, comparable to `Oumuamua, the excess speed of which was 26 km/s.
Following the identification, we obtained short series of g' and r'-band images on 10 September 2019 at 05:38 UT and 14:57 UT, using the William Herschel Telescope on La Palma and the Gemini North telescope on Mauna Kea, respectively. The images show an extended coma and a broad, short tail (roughly antisolar direction), making it clear that this second-known interstellar interloper is a comet.
gb00234 is currently at a low solar elongation of ~43 deg, making more detailed observations difficult. Observing conditions will be improving, though, as the elongation increases and the body is on its way in (perihelion at 1.96 au and perigee at 1.89 au, both in December 2019).
Based in part on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), Ministerio de Ciencia, Tecnologia e Innovacion Productiva (Argentina), and Ministerio da Ciencia, Tecnologia e Inovacao (Brazil). The William Herschel Telescope is operated on the island of La Palma by the Isaac Newton Group of Telescopes in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. We thank the staff of both observatories for assistance and are indebted to the Director of Gemini Observatory for allocating Gemini North time for this program. M.D. and P.G. are grateful for support from the National Science Centre of Poland through SONATA BIS grant 2016/22/E/ST9/00109 and Polish Ministry of Science and Higher Education grant DIR/WK/2018/12. G.C. acknowledges support from European Research Council Consolidator Grant 647208. I.P.M. acknowledges funding from the Netherlands Research School for Astronomy (NOVA5-NW3-10.3.5.14).
