Discovery and designation

A comet was discovered by G. Borisov and reported on 30 August 2019. Determination of its orbit based on additional observations confirmed that it was on a hyperbolic trajectory through the solar system. It was initially designated as comet C/2019 Q4 (Borisov) on 11 September. On 24 September the Minor Planet Center assigned it the designation 2I as the second interstellar object (after 1I/'Oumuamua) with the permanent name Borisov as decided by the IAU Working Group for Small Body Nomenclature.

Orbit and ephemeris (MPC, 2019)

perihelion distance q: eccentricity e: inclination i: ascending node Ω: longitude of perihelion ω: time of perihelion Tp: Epoch: absolute magnitude H: data arc:

1.9402023 AU 3.0794827 44.67800° 307.53784° 210.69784° 2019 Dec 10.23244 2019 Dec 23.0 12 days (2019 Aug 30--Sep 11), 145 obs.

Orbit and ephemeris (JPL, 2019)

perihelion distance q: eccentricity e: inclination i: ascending node Ω: longitude of perihelion ω: mean anomaly M: time of perihelion Tp: Epoch: nongravitational parameter A1: nongravitational parameter A2: nongravitational parameter A3: total magnitude M1: total magnitude slope K1: data arc:

2.006616 ± 0.000022 AU 3.35706 ± 0.00025 44.05352 ± 0.00018° 308.14998 ± 0.00033° 209.12445 ± 0.00050° 34.4378 ± 0.0054° 2019 Dec 08.55440 ± 0.00077 2020 Jan 05.0 (-4.52 ± 3.96) x 10-8 (-3.23 ± 7.02) x 10-8 (1.18 ± 0.18) x 10-7 13.7 ± 0.8 4.5 374 days (2018 Dec 13-2019 Dec 22), 1146 obs.

date	magnitude	distance to Sun (AU)	distance to Earth (AU)	notes
2013 Jan 01	29.77	49.497	48.963
2014 Jan 01	29.15	42.576	42.034
2015 Jan 01	28.41	35.637	35.085
2016 Jan 01	27.5	28.674	28.109
2017 Jan 01	26.33	21.658	21.080
2018 Jan 01	24.67	14.611	13.996
2018 Dec 13	21.99	7.870	7.104	earliest pre-discovery observation
2019 Apr 30	20.74	5.193	5.812	crossed Jupiter's orbit inbound
2019 Aug 30	18.69	2.986	3.722	discovery
2019 Oct 01	17.90	2.515	3.021
2019 Nov 01	17.14	2.173	2.429
2019 Dec 01	16.63	2.014	2.049
2019 Dec 08	16.56	2.007	1.998
2019 Dec 20	16.52	2.023	1.946	brightest as seen from Earth
2019 Dec 28	16.54	2.053	1.937	closest approach to Earth
2020 Jan 01	16.56	2.073	1.939
2020 Feb 01	16.95	2.341	2.076
2020 Mar 01	17.49	2.723	2.326
2020 Apr 01	18.11	3.214	2.668
2020 May 01	18.73	3.735	3.091
2020 Jun 01	19.37	4.302	3.665
2020 Jul 01	19.99	4.865	4.371
2020 Jul 19	20.36	5.208	4.856	crosses Jupiter's orbit outbound
2020 Aug 01	20.61	5.457	5.230
2020 Sep 01	21.17	6.055	6.163
2020 Oct 01	21.64	6.637	7.066
2020 Nov 01	22.06	7.241	7.924
2020 Dec 01	22.40	7.826	8.620
2021 Jan 01	22.68	8.431	9.160
2022 Jan 01	25.12	15.532	16.326
2025 Jan 01	28.59	36.522	37.354
2030 Jan 01	31.32	71.070	71.915
2035 Jan 01	32.94	105.418	106.268
2040 Jan 01	34.09	139.686	140.539
2045 Jan 01	34.99	173.929	174.781
2050 Jan 01	35.73	208.108	208.962

Confirmation as interstellar in origin

Cometary activity

Size

References

--articles and preprints on 2I/Borisov (from newest to oldest; arXiv posting date in parentheses)

• Z. Xing, D. Bodewits, J. Noonan, and M. T. Bannister, (15 Jan. 2020), Water production rates and activity of interstellar comet 2I/Borisov, arXiv, on line 2001.04865.

• T. M. Eubanks, (29 Dec. 2019) Is interstellar object 2I/Borisov a stardust comet? Predictions for the post perihelion period, arXiv, on line 1912.12730.
• C. A. L. Bailer-Jones, D. Farnocchia, Q. Ye, K. J. Meech, and M. Micheli, Jan. 2020 (21 Dec. 2019), A search for the origin of the interstellar comet 2I/Borisov, Astronomy and Astrophysics, 634:A14; arXiv, on line 1912.10213.
• B. T. Bolin, (13 Dec. 2019), Evolving coma morphology of interstellar comet 2I/Borisov with deep HST imaging, arXiv, on line 1912.07386.
• H. W. Lin, C.-H. Lee, D. W. Gerdes, F. C. Adams, J. Becker, K. Napier, and L. Markwardt, 1 Feb. 2020 (12 Dec. 2019), Detection of diatomic carbon in 2I/Borisov, Astrophysical Journal Letters, 889:L30; arXiv, on line 1912.06161.
• C.-H. Lee, H.-W. Lin, Y.-T. Chen, and S.-F. Yen, Dec. 2019 (11 Dec. 2019), FLAMINGOS-2 infrared photometry of 2I/Borisov, Research Notes of the AAS, 12:184; arXiv, on line 1912.05628.
• D. Jewitt, M.-T. Hui, Y. Kim, M. Mutchler, H. Weaver, and J. Agarwal, 10 Jan. 2020 (11 Dec. 2019), The nucleus of interstellar comet 2I/Borisov, Astrophysical Journal Letters, 888:L23; arXiv, on line 1912.05422.
• B. Yang, M. S. P. Kelley, K. J. Meech, J. V. Keane, S. Protopapa, and S. J. Bus, Jan. 2020 (11 Dec. 2019), Searching for water ice in the coma of interstellar object 2I/Borisov, Astronomy and Astrophysics, 634:L6; arXiv, on line 1912.05318.
• Z. Sekanina, (18 Nov. 2019), Sublimation of water ice from a population of large, long-lasting grains near the nucleus of 2I/Borisov?, arXiv, on line 1911.06271.
• Q. Ye, et al., Feb. 2020 (23 Dec. 2019), Pre-discovery activity of new interstellar comet 2I/Borisov beyond 5 AU, Astronomical Journal, 159:77; arXiv, on line 1911.05902.
• A. Higuchi and E. Kokubo, Nov. 2019 (11 Nov. 2019), Hyperbolic orbits in the Solar System: Interstellar origin or perturbed Oort cloud comets?, Monthly Notices of the Royal Astronomical Society; arXiv, on line 1911.04524.
• T. Hallatt and P. Wiegert, (6 Nov. 2019), The dynamics of interstellar asteroids and comets within the galaxy: An assessment of local candidate source regions for 1I/`Oumuamua and 2I/Borisov, arXiv, on line 1911.02473.
• B. T. Bolin, et al., (5 Nov. 2019), Characterization of the nucleus, morphology and activity of interstellar comet 2I/Borisov by optical and near-infrared GROWTH, Apache Point, IRTF, ZTF and Keck observations, arXiv, on line 1910.14004.
• A. J. McKay, A. L. Cochran, N. D. Russo, and M. DiSanti, 20 Jan. 2020 (28 Oct. 2019), Detection of a water tracer in interstellar comet 2I/Borisov, Astrophysical Journal Letters, 889:L10; arXiv, on line 1910.12785.
• Z. Sekanina, (24 Oct. 2019), Note on the HST image of comet 2I/Borisov taken on 2019 October 12, arXiv, on line 1910.11457.
• C. Opitom, et al., Nov. 2019 (25 Oct. 2019), 2I/Borisov: A C2 depleted interstellar comet, Astronomy and Astrophysics, 631:L8; arXiv, on line 1910.09078.
• Z. Sekanina, (22 Oct. 2019), Are 2I/Borisov and Oort cloud comets alike?, arXiv, on line 1910.08208.
• T. Hands and W. Dehnen, Dec. 2019 (14 Oct. 2019), Capture of interstellar objects: a source of long-period comets, Monthly Notices of the Royal Astronomical Society; arXiv, on line 1910.06338.
• T. Kareta, et al., (25 Nov. 2019), Carbon chain depletion of 2I/Borisov, arXiv, on line 1910.03222.
• D. Jewitt and J. Luu, Dec. 2019 (26 Nov. 2019), Initial characterization of interstellar comet 2I/2019 Q4 (Borisov), Astrophysical Journal Letters, 886:L29; arXiv, on line 1910.02547.
• D. Bamberger and G. Wells, Oct. 2019, The difficulty of predicting stellar occultations by interstellar comet 2I/Borisov, Research Notes of the AAS, 10:159.
• A. Kochergin, et al., Oct. 2019, Velocity of dust ejected from interstellar comet 2I/Borisov, Research Notes of the AAS, 10:152.
• A. Fitzsimmons, et al., Nov. 2019 (2 Oct. 2019), Detection of CN gas in interstellar object 2I/Borisov, Astrophysical Journal Letters, 885:L9; arXiv, on line 1909.12144.
• P. A. Dybczynski, M. Krolikowska, and R. Wysoczanska, (26 Nov. 2019), Kruger 60 as a home system for 2I/Borisov--a case study, arXiv, on line 1909.10952.
• E. Zubko, E. Chornaya, G. Videen, and S. S. Kim, Sept. 2019, Clues to understanding the microphysics of dust in the interstellar comet C/2019 Q4 (Borisov), Research Notes of the AAS, 9:138.
• J. de Leon, J. Licandro, M. Serra-Ricart, A. Cabrera-Lavers, J. Font Serra, R. Scarpa, C. de la Fuente Marcos, and R. de la Fuente Marcos, Sept. 2019, Interstellar visitors: A physical characterization of comet C/2019 Q4 (Borisov) with OSIRIS at the 10.4 m GTC, Research Notes of the AAS, 9:131.
• A. Siraj and A. Loeb, (16 Sept. 2019), An argument for a kilometer-scale nucleus of C/2019 Q4, arXiv, on line 1909.07286.
• A. Hibberd, N. Perakis, and A. M. Hein, (13 Sept. 2019), Sending a spacecraft to interstellar comet C/2019 Q4 (Borisov), arXiv, on line 1909.06348.
• P. Guzik, M. Drahus, K. Rusek, W. Waniak, G. Cannizzaro, and I. Pastor-Marazuela, Oct. 2019 (14 Oct. 2019), Initial characterization of interstellar comet 2I/Borisov, Nature Astronomy; arXiv, on line 1909.05851.

--other items on 2I/Borisov (from newest to oldest)

• W. W. Gibbs, Nov. 2019, "Alien comets may be common, analysis of 2I/Borisov suggests," Science, 366(6465):558.
• Nature, Oct. 2019, "The comet that came in from interstellar space," Nature, 574(7779):456.
• P. Gilster, 12 Sept. 2019, "C/2019 Q4 (Borisov): A likely interstellar comet," Centauri Dreams, on line [https://www.centauri-dreams.org/2019/09/12/c-2019-q4-borisov-a-likely-interstellar-comet/].
• B. King, 11 Sept. 2019, "Another interstellar visitor is headed our way," Sky and Telescope, on elin [https://www.skyandtelescope.com/astronomy-news/possible-interstellar-comet-headed-our-way/].

--Minor Planet Center releases on 2I/Borisov

• MPC, 11 Sept. 2019, Comet C/2019 Q4 (Borisov), MPEC 2019-R106.
• MPC, 13 Sept. 2019, Comet C/2019 Q4 (Borisov), MPEC 2019-R113.
• MPC, 23 Sept. 2019, Comet C/2019 Q4 (Borisov), MPEC 2019-S62.
• MPC, 24 Sept. 2019, 2I/Borisov = C/2019 Q4 (Borisov), MPEC 2019-S72.
• MPC, 2 Oct. 2019, Comet 2I/Borisov, MPEC 2019-T44.
• MPC, 7 Oct. 2019, Comet 2I/Borisov, MPEC 2019-T116.
• MPC, 22 Oct. 2019, Comet 2I/Borisov, MPEC 2019-U80.
• MPC, 3 Nov. 2019, Comet 2I/Borisov, MPEC 2019-V34.
• MPC, 7 Nov. 2019, Observations and orbits of comets, MPEC 2019-V116.
• MPC, 8 Nov. 2019, Comet 2I/Borisov, MPEC 2019-V130.
• MPC, 18 Nov. 2019, 2I/Borisov, MPEC 2019-W50.
• MPC, 8 Dec. 2019, Observations and orbits of comets and A/ objects, MPEC 2019-X94.

--International Astronomical Union releases on 2I/Borisov (requires subscription)

• MPC, 12 Sept. 2019, Comet 2I/2019 Q4 (Borisov), CBET 4666.
• MPC, 18 Sept. 2019, Comet 2I/2019 Q4 (Borisov), CBET 4668.
• MPC, 21 Sept. 2019, Comet 2I/2019 Q4 (Borisov), CBET 4669.
• MPC, 21 Sept. 2019, Comet 2I/2019 Q4 (Borisov), CBET 4670.
• MPC, 29 Sept. 2019, Comet 2I/2019 Q4 (Borisov), CBET 4672.
• MPC, 18 Oct. 2019, Comet 2I/2019 Q4 (Borisov), CBET 4679.
• MPC, 3 Nov. 2019, Comet 2I/2019 Q4 (Borisov), CBET 4691.
• MPC, 9 Jan. 2020, Comet 2I/2019 Q4 (Borisov), CBET 4710.
• MPC, 30 Jan. 2020, Comet 2I/2019 Q4 (Borisov), CBET 4719.

--background articles and data sets

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Last modified 1 February 2020.
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