Thecomet nucleus was estimated to be about a kilometer in size,[10] rotating every 8.5[6] to 8.7 hours.[7] Itstails of dust and gas extended for millions of kilometers and, during January 2023, ananti-tail was also visible.[11]
The comet reached itsperihelion on 12 January 2023, at a distance of 1.11 AU (166 million km; 103 million mi), and the closest approach toEarth was on 1 February 2023, at a distance of 0.28 AU (42 million km; 26 million mi). The comet reachedmagnitude 5 and was visible with thenaked eye under moonlessdark skies.[12][13][14][15]
The object was initially identified as anasteroid, but subsequent observations revealed it had a very condensedcoma, indicating it is a comet.[18] H. Sato reported its coma was 8arcseconds across in stacked photos he obtained from theremote observatory in Mayhill, New Mexico, while K. Yoshimoto reported its coma was 15 arcseconds across and the comet had a small tail 25 arcseconds long.[1][16] The comet in stacked ZTF images appeared extended when compared to nearby stars and was flagged as a comet by the Tails neural network.[17]
The dust tail and the coma were gradually getting bigger as the comet was approaching the Sun between July and October 2022, and dust production rose from 241 ± 3 kg/s in July to 476 ± 9 kg/s.[20] By early November 2022, the comet had brightened to magnitude 10 and was appearing to move slowly inCorona Borealis andSerpens as it moved parallel to Earth.[21] The comet exhibited a green coma and a yellowish dust tail and a faint ion tail. The comet was visible in the early evening and started being visible in the morning sky by the end of November.[22] By 19 December, the comet had developed a greenish coma, a short, broad dust tail, and a long faint ion tail stretching across a 2.5-degree wide field of view.[23] After that, the comet started moving northward, passing throughBoötes,Draco, andUrsa Minor, passing within about 10 degrees ofPolaris by the end of January.[22][24]
The comet on 24 January 2023, with the antitail towards the left
The comet reached its perihelion on 12 January 2023, at a distance of 1.11 AU (166 million km; 103 million mi).[25][26] The first naked-eye observations of the comet occurred on 16 and 17 January, with the comet having an estimated magnitude of 5.4 and 6.0 respectively.[27] Strongsolar wind from acoronal mass ejection caused a disconnection event of the ion tail of the comet on 17 January, making it appear broken.[28] On 22 January ananti-tail became visible. This tail appears pointing toward the Sun and opposite the dust and ion tails. It is caused by particles lying on a disk on the orbital plane of the comet, and when Earth aligns with that plane, they look like a reverse tail.[29][30]XMM-Newton X-ray space telescope observed the comet on 23 January, but it was only faintly detected.[31][32]
The comet's closest approach to Earth was on 1 February 2023, at a distance of 0.28 AU (42 million km; 26 million mi). As of 31 January 2023, the comet had anapparent magnitude of about 5; its coma was reported to be about 20' across.[12] The central region of the coma measured bout 4 arcminutes across, which corresponds to diameter of 50,000 km, and featured two jets about 20 arcseconds long.[17] During its closest approach to Earth, it was near the northcelestial pole[33] and located within theCamelopardalis constellation.[34] The moon was awaxing gibbous and the brightening moon hampered viewing the comet without optical aid.[35] On 5 February, at the full moon, the comet passed 1.5 degrees from the bright starCapella.[35] On 6 February, C/2022 E3 (ZTF) visually passed near comet C/2022 U2 (ATLAS).[36] On 10 to 11 February, the comet passed 1.5 degrees fromMars and, on 13 to 15 February, passed in front of theHyades star cluster.[22]
Positions of the comet C/2022 E3 (ZTF) in the starry sky between 14 January and 16 February 2023
C/2022 E3 closest Earth approach on 1 February 2023 17:55 UT[4]
The nucleus of the comet was found to rotate every 8.5[6] to 8.7 hours.[7] In the spectrum of the comet in the wavelength range between 5000 and 7000 Å many emission lines of NH2, C2, and [OI] are detected.[37][38] Thespectrum of the comet was obtained on 10 March 2023 and lines associated withCN, diatomic andtriatomic carbon and possibly OI. The ratio of C2 to CN is about 0.6, which is lower when compared to most of the Solar System comets, although not too low to be considered depleted.[17] Other species detected in the comet includehydrocyan,hydrogen isocyanide,CH3CN,isocyanic acid,formamide,methanol,formaldehyde,formic acid,acetaldehyde,H2S,carbon monosulfide,carbonyl sulfide,ethanol and(CH2OH)2. The comet was depleted in hypervolatiles (lowCO and H2S abundances relative to water) and had a relatively low methanol abundance relative to water (1.8%) compared to the mean of other comets.[39]
The green color is likely due to the presence ofdiatomic carbon, chiefly around the comet's head.[40][41] The C2 molecule, when excited by the solar ultraviolet radiation, emits mostly in infrared, but itstriplet state radiates at 518 nm (nanometers). It is produced byphotolysis oforganic materials evaporated from the nucleus. It then undergoes further photolysis, with a lifetime of about two days, at which time the green glow appears in the comet's head but not the tail.[42][43] The comet researcher Matthew Knight opined that the green color of this comet is not unusual for comets with a higher gas content, but they only rarely approach the Earth as close so it provides for very good observation of the greenish hue.[44] Similar colors were seen with observations of cometC/2021 A1 (Leonard).[45]
Before perihelion passageJPL Horizons showed thebarycentric outbound orbit to be bound to the Sun+Jupiter system at anepoch in the year 2050, but with an unrealistic maximum distance of 270,000 AU (4.3 ly) which is beyond theOort cloud.[2] Post perihelion, the outbound orbit solution is only weakly bound to the Sun.[3] Using a heliocentric orbit at epoch 2495 with just the Sun's mass shows the comet unbound to the Solar System.[46] TheSun's escape velocity at 200 AU is 2.98 km/s[47] and the comet will be going 2.97 km/s at 200 AU from the Sun.[48] The comet will either leave the Solar System altogether or return in many millions of years depending on perturbations from outgassing (non-gravitational forces) or perturbations while in the Oort cloud by thegalactic tide andpassing stars.[49]
^Biver, N.; Bockelée-Morvan, D.; Handzlik, B.; Sandqvist, Aa.; Boissier, J.; Drozdovskaya, M. N.; Moreno, R.; Crovisier, J.; Lis, D. C.; Cordiner, M.; Milam, S.; Roth, N. X.; Bonev, B. P.; Dello Russo, N.; Vervack, R.; Opitom, C.; Kawakita, H. (October 2024). "Chemical composition of comets C/2021 A1 (Leonard) and C/2022 E3 (ZTF) from radio spectroscopy and the abundance of HCOOH and HNCO in comets".Astronomy & Astrophysics.690: A271.arXiv:2408.10759.Bibcode:2024A&A...690A.271B.doi:10.1051/0004-6361/202450921.
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