BAA Comet Section : Comets discovered in 2021

Updated 2021 March 22


  • 2021 A1 (Leonard)
  • 2021 A2 (NEOWISE)
  • 2021 A3 (P/STEREO)
  • 2021 A4 (NEOWISE)
  • 2021 A5 (P/PanSTARRS)
  • 2021 A6 (PanSTARRS)
  • 2021 A7 (NEOWISE)
  • 2021 A8 (P/Scotti)
  • 2021 A9 (PanSTARRS)
  • 2021 A10 (NEOWISE)
  • 2021 A11 (P/PanSTARRS)
  • 2021 B1 (P/NEOWISE)
  • 2021 B2 (PanSTARRS)
  • 2021 B3 (NEOWISE)
  • 2021 C1 (Rankin)
  • 2021 C2 (P/PanSTARRS)
  • 2021 C3 (Catalina)
  • 2021 C4 (ATLAS)
  • 2021 C5 (PanSTARRS)
  • 2021 C6 (Lemmon)
  • 2021 CT3 [A/PanSTARRS]
  • 2021 D1 (SWAN)
  • 2021 D2 (ZTF)
  • 2021 E1 (P/Hill)

  • When observing a comet please try to forget how bright you think the comet should be, what it was when you last viewed it, what other observers think it is or what the ephemeris says it should be.

    The equations for the light curves of comets that are currently visible use only the raw observations and should give a reasonable prediction for the current brightness. If the comet has not yet been observed or has gone from view a correction for aperture is included, so that telescopic observers should expect the comet to be fainter than given by the equation. The correction is about 0.033 per centimetre. Values for the r parameter given in square brackets [ ] are assumed. The form of the light curve is either the standard m = H0 + 5 log d + K0 log r or the linear brightening m = H0 + 5 log d + L0 abs(t - T + D0) where T is the date of perihelion, t the present and D0 an offset, if L0 is +ve the comet brightens towards perihelion and if D0 is +ve the comet is brightest prior to perihelion.

    Observations of comets in 2021 are given in ICQ format. 

    Full details of recently discovered objects will not appear until they are available on the CBAT web pages. The actual accuracy of preliminary orbits is often (nearly always) much worse than the published accuracy implies.  In part this is because each orbital solution is treated as a mathematical construct and does not take account of observational error.  JPL does publish the errors, whereas the MPECs do not.


    2021 A1 (Leonard)
    Gregory Leonard discovered a comet of 19th magnitude in images taken with the 1.5m reflector of the Mt Lemmon Survey on 2021 January 3.54. It was placed on the PCCP as C4AGJ62. There were prediscovery observations from Catalina Sky Survey (2020 December, 2021 January), Mt Lemmon Survey (2020 April, November), PanSTARRS (2020 April, May, June, August) and the Szeged Asteroid Program, Hungary (2020 November). [CBET 4907, MPEC 2021-A99, 2021 January 10]. The comet is at perihelion at 0.6 au in 2022 January. The comet will pass 0.23 au from the earth on 2021 December 12 and 0.0286 au from Venus on 2021 December 18.  The comet could come within visual range in 2021 October and reach 4th magnitude in December during its approach to Earth.  It then goes into solar conjunction and becomes poorly placed for northern observers.  Southern hemisphere observers will see it fading from 5th magnitude after conjunction later in December.
    2021 A2 (NEOWISE)
    An approximately 15th magnitude comet was discovered from the NEOWISE satellite on 2021 January 3.02. It was posted on the PCCP as N00ht7m. Ground-based observers confirmed the cometary nature, with Michael Mattiazzo reporting it as bright as 12th magnitude in his 0.2 m reflector. [CBET 4908, MPEC 2021-A100, 2021 January 10] It is at perihelion at 1.4 au in 2021 January. A southern circumpolar object at discovery, it is rapidly moving north and could brighten by a further magnitude.  For some reason the MPC leave it un-named in MPEC 2021-B143 [2021 January 31]
    2021 A3 (414P/STEREO)
    An object was discovered by the Zwicky Transient Factory on January 5.1 and posted on the PCCP as ZTF01on. It was summarily removed on January 8 and noted to be P/2016 J3. The previous evening Maik Meyer had discovered the identity, computed a linked orbit and informed the MPC and CBAT.  Maik's linked orbit shows that the period is 4.67 years, with perihelion at 0.53 au on January 25.  Despite this it has not been designated 2021 A1.  Michael Jaeger has imaged it, finding it to be around 14th magnitude.

    Sam Dean notes:

    It's caught in a Kozai resonance with Jupiter that it's currently on the higher-e, lower-i leg of. I think that'll peak around 2400-2500 before cycling back. Like plenty of Earth-crossing Kozai oscillating objects, its orbit also crosses Earth sometimes, creating a potential for meteor showers. It last crossed Earth's orbit within 0.1 au in the 1300s, coming as close as 0.07 au - and it will next do so in the 2200s/2300s, coming less than 0.01 au around 2300, where it should create a fairly regular and impressive meteor shower considering that it would be even more active than it is now.
    Sam also suggests that the absolute magnitude is very faint, around 23 and that it brightens rapidly, perhaps at 20 log r.

    Rather belatedly the CBAT issued CBET 4911 on January 11, with a revision coming 15 minutes later.  This gives a similar account to that given above and notes that the comet will pass Jupiter at 0.9 au in 2031 December.  It also hints that either the comet shows strong non-gravitational forces or that the 2016 positions are somewhat out. The MPC finally issued MPEC 2021-A157 on January 12. This does not give elements for 2016, although the published elements do use observations from 2016, so it may just be an oversight.  Perhaps because of the delays it also briefly appeared on the PCCP as P11c5Dk.
    2021 A4 (NEOWISE)
    An approximately 20th magnitude comet was discovered from the NEOWISE satellite on 2021 January 3.92. It was posted on the PCCP as N00htdm. The MPEC suggests that it was reported by NEOWISE as being cometary, however the CBET suggests that it was reported because of interesting motion and that ground-based observers confirmed the cometary nature. There were prediscovery observations from PanSTARRS on January 3.6. [CBET 4914, MPEC 2021-A207, 2021 January 15] It is at perihelion at 1.1 au in 2021 March. It appears to be an intrinsically faint object and if so won't come within visual range. Discovery magnitudes of NEOWISE objects are often fainter than seen by visual observers.  Alan Hale reported the comet as being 12.6 on February 6.16.
    2021 A5 (P/PanSTARRS)
    PanSTARRS 1 discovered a 21st magnitude comet in images taken with the 1.8m Ritchey-Chretien on January 6.30. It was placed on the PCCP as P11bxkC. There were prediscovery Mt Lemmon observations from 2020 December 16. [CBET 4915, MPEC 2021-A209, 2021 January 15] The comet was at perihelion at 2.6 au in 2020 November and has a period of 5.3 years.
    2021 A6 (PanSTARRS)
    PanSTARRS 1 discovered a 21st magnitude comet in images taken with the 1.8m Ritchey-Chretien on January 8.60. It was placed on the PCCP as P11bKhA. There were prediscovery Mt Lemmon observations from 2020 November 26 and December 22. [CBET 4916, MPEC 2021-A210, 2021 January 15] The comet was at perihelion at 7.9 au in 2021 April.
    2021 A7 (NEOWISE)
    An approximately 20th magnitude comet was discovered from the NEOWISE satellite on 2021 January 9.11. It was posted on the PCCP as N00hue0. [CBET 4917, MPEC 2021-A211, 2021 January 15/16] It is at perihelion at 2.0 au in 2021 July.  The CBET suggests that there is a possibility that it may be an intermediate period comet.
    2021 A8 (416P/Scotti)
    Erwin Schwab recovered comet 2013 A2 as a nearly stellar object in images taken with the 0.8-m f/3 Schmidt reflector at Calar Alto, Spain, on January 14.01. [CBET 4919, MPEC 2021-B21, 2021 January 17]
    2021 A9 (PanSTARRS)
    PanSTARRS 1 discovered a 21st magnitude comet in images taken with the 1.8m Ritchey-Chretien on January 12.64. It was placed on the PCCP as P11bX5O. There were prediscovery Mt Lemmon observations from 2020 December 12 and 2021 January 9, and PanSTARRS 2 observations from 2020 December 24.  It may be an intermediate period comet.  [CBET 4922, MPEC 2021-B119, 2021 January 23] The comet is at perihelion at 7.7 au in 2023 November.
    2021 A10 (NEOWISE)
    An approximately 19th magnitude potential NEO was discovered from the NEOWISE satellite on 2021 January 12.16. It was posted on the PCCP as N00hurv. Subsequently astrometrists, including Peter Birtwhistle noted cometary features; Nick James also reported astrometry. [CBET 4930, MPEC 2021-C25, 2021 February 6] It is at perihelion at 1.3 au in 2021 March and has a long period, retrograde orbit. 
    2021 A11 (P/PanSTARRS)
    Erwin Schwab recovered comet 2015 F1 as an apparently stellar object in images taken with the 0.8-m f/3 Schmidt reflector at Calar Alto, Spain, on January 13.06. Additional observations were made on February 10, 13 and 14. The comet was some 4' from the predicted position, implying a delta T of -0.2 days. The comet passed 0.46 au from Jupiter in 1975 December in an encounter that substantially reduced the perihelion distance. The comet is significantly fainter at this return than it was at the discovery return. [CBET 4933, MPEC 2021-D104, 2021 February 16/25].  It is not clear why there was such a long gap between the issue of the CBET and MPEC.
    2021 B1 (417P/NEOWISE)
    Erwin Schwab recovered comet 2015 J3 as a nearly stellar object in images taken with the 0.8-m f/3 Schmidt reflector at Calar Alto, Spain, on January 17.23. The comet passed 0.48 au from Jupiter in 1952 August and will pass 0.43 au from the planet in 2024 September in an encounter that will increase the perihelion distance from 1.49 to 1.57 au. [CBET 4920, MPEC 2021-B118, 2021 January 22/23]
    2021 B2 (PanSTARRS)
    PanSTARRS 1 discovered a 20th magnitude comet in images taken with the 1.8m Ritchey-Chretien on January 17.23. It was placed on the PCCP as P11cite. There were prediscovery Catalina Sky Survey observations from 2020 December 12 and PanSTARRS 1 observations from 2020 December 24. [CBET 4921, MPEC 2021-B120, 2021 January 23] The comet is at perihelion at 2.5 au in 2021 May.
    2021 B3 (NEOWISE)
    An approximately 19th magnitude comet was discovered from the NEOWISE satellite on 2021 January 22.25. It was posted on the PCCP as N00hwa7. [CBET 4929, MPEC 2021-C16, 2021 February 4] It is at perihelion at 2.2 au in 2021 March and has a period of around 150 years
    2021 C1 (Rankin)
    David Rankin discovered a comet of 20th magnitude in images taken with the 1.5m reflector on February 11.44 during the Mt Lemmon Survey. It was placed on the PCCP as C4WH682. [CBET 4934, MPEC 2021-D102, 2021 February 24/25]. The comet was at perihelion at 3.5 au in 2020 December.
    2021 C2 (P/PanSTARRS)
    PanSTARRS 1 discovered a 22nd magnitude comet in images taken with the 1.8m Ritchey-Chretien on February 12.53. It was placed on the PCCP as P11dgUs. There were prediscovery Mt Lemmon observations from 2021 January 17. [CBET 4935, MPEC 2021-D103, 2021 February 24/25] The comet was near perihelion at 4.9 au and has a period of around 30 years.
    2021 C3 (Catalina)
    An object of 19th magnitude was discovered in Catalina Sky Survey images taken with the 0.68m Schmidt on February 7.46. PanSTARRS 1 reported cometary features and it was placed on the PCCP as C1VUXJ1. There were pre-discovery Catalina images from January 16. [MPEC 2021-D112, CBET 4936, 2021 February 26]. The comet was near perihelion at 2.3 au and has a period of around 500 years in a retrograde orbit.
    2021 C4 (ATLAS)
    A 19th magnitude object was discovered in images taken with the 0.5m Schmidt at Haleakala on February 12.61 by the ATLAS (Asteroid Terrestrial-impact Last Alert System) team. It was posted on the PCCP as A10vcA4 following reports of signs of cometary activity. [CBET 4937, MPEC 2021-D113, 2021 February 26]. The comet was at perihelion at 4.5 au in 2021 January.
    2021 C5 (PanSTARRS)
    PanSTARRS 1 discovered a 21st magnitude comet in images taken with the 1.8m Ritchey-Chretien on February 12.35. It was placed on the PCCP as P11dcTx. There were prediscovery PanSTARRS observations from 2020 December 22 2021 January 23 and February 6 and Mt Lemmon observations from 2021 January 18. [CBET 4941, MPEC 2021-E64, 2021 March 8] The comet is at perihelion at 3.2 au in 2023 February.
    2021 C6 (Lemmon)
    The Mt Lemmon Survey discovered a potential NEO of 21st magnitude in images taken with the 1.5m reflector on February 7.43. It was placed on the PCCP as C4V28F2. Confirmation astrometry showed cometary features and pre-discovery images from PanSTARRS were found from January 23. [CBET 4946, MPEC 2021-F63, 2021 March 21]. The comet is at perihelion at 3.3 au in 2021 November. It is in a hyperbolic retrograde orbit.
    2021 CT3 [A/PanSTARRS]
    PanSTARRS 1 discovered an asteroid in images taken with the 1.8m Ritchey-Chretien on 2021 February 7.37. The object, classified by JPL as a Centaur, is at perihelion at 4.3 au in 2021 December and is in a retrograde orbit with a period of around 20 years. It briefly appeared on the PCCP as P11czUb.
    2021 D1 (SWAN)
    Michael Mattiazzo discovered a comet on February 25 in SWAN images taken since February 19 and this was confirmed in ground based images taken by Michael Jaeger on February 28.  The comet is currently poorly placed for visual observation, but is imageable.  The comet was near perihelion at 0.9 au and will fade.  Nick James, Denis Buczynski, Werner Hasubick and Richard Miles all made confirmatory images and astrometery of the comet. The MPC published an orbit and designated the comet in MPEC 2021-E19 [2021 March 4]. This gave an orbit with a period of around 75 years. CBET 4939 appeared five hours later on March 5 and gave a parabolic orbit based on a shorter arc with fewer observations, though with much more detail about the confirming observations.
    2021 D2 (ZTF)
    The Zwicky Transient Facility reported observations of a 19th magnitude possible NEO made on February 19.55 with the 1.2m Oschin Schmidt. This was placed on the PCCP as ZTF0KcP and subsequently found to show cometary features by astrometrists.  The CBET note that it is the same object as ZTF0Kii reported on March 13.7  [CBET 4947, MPEC 2021-F67, 2021 March 22]. The comet is at perihelion at 2.9 au in 2022 February.
    2021 E1 (P/Hill)
    Erwin Schwab recovered comet 2009 Q1 as a stellar object in images taken with the 0.8-m f/3 Schmidt reflector at Calar Alto, Spain, on March 11.13. The recovery was confirmed by Diana Abreu using the 1.0m reflector at the ESA Optical Ground Station, Tenerife on March 14. The comet was some 9' from the expected position and does not reach perihelion until 2022 May. When Syuichi Nakano computed a linked orbit the observations showed that non-gravitiational parameters were required. When these were included it was found that the 1996 observations reported by Rob Matson were of the comet, though his 1998 measurements did not fit so well. [CBET 4943, MPEC 2021-F07, 2021 March 16/17]
    Ephemerides of current comets are available on the CBAT ephemeris page and positions of newly discovered comets are on the Possible Comet Confirmation Page.
    More information on LINEAR. A list of comets discovered by selected search programs.
    The Northumberland refractor is the telescope that was used in the search for Neptune. It now has a 0.30-m f20 doublet lens which gives a stellar limiting magnitude of around 15 at the zenith on good nights. The Thorrowgood refractor was built in 1864 and has a 0.20-m f14 doublet lens; it is currently out of action as the dome has stuck.
    Published by Jonathan Shanklin. Jon Shanklin - jds@ast.cam.ac.uk