The brighter comets of 2019

A report of the Comet Section. Director: N. D. James.

This report describes and analyses the observations of the brighter or more interesting comets at perihelion during 2019, concentrating on those with visual observations. Magnitude parameters are given for all comets with observations. Any evolution in the magnitude parameters of those periodic comets with multiple returns is discussed. Additional information on the comets discussed here, and on other comets seen or at perihelion during the year, may be found on the Section visual observations web pages.


87 comets or potential comets were assigned year designations for 2019 and 35 previously numbered periodic comets returned to perihelion. 212 comets detected by the SOHO satellite and 14 by STEREO were credited during 2019. 182 were members of the Kreutz group, 21 of the Meyer group, one of the Marsden group, four of the Kracht group and 18 were not associated with any known group. None of these objects were given a designation, though 322P/SOHO returned to perihelion. There were two possible amateur discoveries (2019 Q4 and V1), for which Gennady Borisov may gain the Edgar Wilson Award, though there has been no formal announcement to date. 18 periodic comets were numbered during the year. Two comets were reported as visible to the naked eye (though one was at perihelion in 2018) and two others reached binocular brightness.

Figure 1. 2018 Y1 imaged near NGC 2903 by the Gruppo Astrofili Palidoro, on 2019 Feb 13. Evostar 80ED and ASI 385MC.


The remainder of this report covers only the comets that were at perihelion during the year. When periodic comets have visual or electronic observations at five or more returns and have not previously been analysed in detail over the past decade, the secular behaviour of the comet is considered, even though it may not qualify as a ‘brighter’ comet during the present return. Any evolution in behaviour is of interest, as is observation of a steady state.

Orbital elements for all the comets discovered and returning during the year can be found on the JPL Small-Body Database Browser,1 which will also generate ephemerides. Discovery details and further information for the other comets found or returning during the year are available on the Section visual observations web pages,2 which also contain links to additional background information. The raw visual observations for the year are on the Section visual observations web pages in ICQ format, and in the Comet Observations database (COBS).3 The full dataset from COBS is used for the multi-return analyses presented here, but otherwise only those submitted to the Section – directly, through The Astronomer magazine, or via COBS – are included. Additional images of the comets are presented in the Section image archive.4


The comets given a discovery designation

2018 N2 (ASASSN)

The All-Sky Automated Survey for Supernovae (ASAS-SN) discovered a 16th-magnitude comet with the ‘Cassius’ 14cm telescope at Cerro Tololo on 2018 Jul 7.39. [CBET 4534, MPEC 2018-O1, 2018 Jul 16.] The comet reached perihelion at 3.1au in 2019 November, when it was 11th magnitude. That this was one of the brighter comets of the year says something about the paucity of brighter objects. It is still under observation by imagers.


2018 R3 (Lemmon)

An apparently asteroidal object of 19th magnitude was found in Mt Lemmon Survey images taken with the 1.5m reflector on 2018 Sep 7.16. It was placed on the Minor Planet Center’s Possible Comet Confirmation Page (PCCP) as ZRBBF83, and follow-up observations by astrometrists showed that it was slightly diffuse and elongated. With a preliminary orbit, Gareth Williams was then able to find pre-discovery Pan-STARRS images from 2018 August. [CBET 4556, MPEC 2018-S04, 2018 Sep 16.] The comet was at perihelion at 1.3au in 2019 June, when it reached 9th magnitude.


2018 W2 (Africano)

Brian Africano discovered a comet of 18th magnitude in Mt Lemmon Survey images taken with the 1.5m reflector on 2018 Nov 27.53. It was discovered at almost the same time by Hannes Gröller in images taken by the Catalina Sky Survey with the 0.68m Schmidt on Nov 27.51, but his report arrived after the one from Mt Lemmon. [CBET 4580, MPEC 2018-X23, 2018 Dec 3.] The comet was at perihelion at 1.5au in 2019 September. It brightened quite rapidly and reached 9th magnitude in late September.

Figure 2. The observations of 2018 Y1 with a standard light curve fitted to them. The dashed lines show the 95% confidence limits.

2018 Y1 (Iwamoto)

Masayuki Iwamoto (Awa, Tokushima, Japan) discovered another comet in images taken on 2018 Dec 18.84 with a 10cm ƒ/4.0 Pentax SDUF II telephoto lens and a Canon EOS 6D camera. The comet was around 13th magnitude with a well condensed coma. [CBET 4588, MPEC 2018-Y52, 2018 Dec 20.] The comet was discovered as it emerged from solar conjunction but would have been discoverable by a southern-hemisphere survey telescope earlier in the year. It was approaching perihelion in early February at 1.3au and passed 0.3au from Earth on Feb 12. It became visible from the UK during mid-January in the early morning sky, but was quickly moving north as it approached Earth and was visible all night by mid-February. Kevin Hills and Nick James contributed astrometry.

The Astronomer contributor Graham Wolf observed the comet from Australia on 2019 Jan 1, estimating its magnitude at 9.4 in his 0.12m reflector. Later that month, Stephen Getliffe was estimating it at 7.7 on Jan 30 in his 0.11m reflector. Jonathan Shanklin, observing from near Chester on Feb 4/5, made it 7.1 in 20×80 binoculars. It was a large and diffuse object, with a 12-arcminute diameter to the coma. The comet was brightest mid-month, with Jose Gonzalez able to see it with the naked eye from his mountain observing site in Spain. By the end of February it was fading rapidly, with Mike Collins reporting it at 9.1 in his 0.25m Schmidt–Cassegrain. Little tail development was seen, with those who did see a tail mostly finding it no more than 20 arcminutes long.

Figure 3. 2018 Y1 imaged by Rolando Ligustri on 2019 Mar 2, when the comet was near the nebula field of AE Aurigae. APO 106/530 and ProLine PL11002 CCD; L = 5×300s.

2I/Borisov = 2019 Q4

Gennady Borisov discovered a comet in images taken with the MARGO 0.65m ƒ/1.5 astrograph at Nauchnij, Crimea on 2019 Aug 30.04. Initial observations suggested a very hyperbolic orbit with an eccentricity of 3.1, implying an interstellar origin. [CBET 4666, MPEC 2019-R106, 2019 Sep 11.] The latest JPL orbit gives an eccentricity of 3.36. The comet reached perihelion at 2.0au in 2019 December.

MPEC 2019-S72 [2019 Sep 24] noted: ‘Continued observation and analysis of this object has confirmed its hyperbolic orbit and interstellar origin. The Minor Planet Center has therefore assigned the permanent interstellar designation 2I to it. The IAU Working Group for Small Body Nomenclature has decided to retain the name Borisov for the permanent designation.’ Nick James provided further information about the comet in the Journal.5

Observations by the Hubble Space Telescope in late March of 2020 led to the suggestion of a possible splitting of the nucleus between Mar 23 & 28. Subsequent observations, however, suggested that the event was only a large outburst. Such outbursts are a normal part of cometary evolution, where most mass loss takes place through outgassing and ejection of small fragments, with infrequent ejection of larger fragments. A similar process takes place at the margin of floating terrestrial ice-shelves, where most loss is via small icebergs, but the occasional large one makes the headlines.

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