.jpg) Comet Tsuchinshan-ATLAS photographed fromOhio, USA on 17 October 2024 | |
| Discovery[1] | |
|---|---|
| Discovery site | Purple Mountain Obs. ATLAS–SAAO (M22) |
| Discovery date | 9 January 2023 |
| Designations | |
| C/2023 A3 | |
| A10SVYR[1] | |
| Orbital characteristics[2][3][4] | |
| Epoch | 10 February 2024 (JD 2460350.5) |
| Observation arc | 3.5 years (1,280 days) |
| Earliestprecovery date | 9 April 2022 |
| Number of observations | 7240 |
| Aphelion | ≈380,000 AU (inbound) |
| Perihelion | 0.39143 AU |
| Semi-major axis | ≈190,000 AU (inbound) |
| Eccentricity | 0.9999797 (inbound) 1.0000353 (outbound) |
| Orbital period | ≈83 million years (inbound) Ejection trajectory (outbound) |
| Max.orbital speed | 67.33 km/s |
| Inclination | 139.112° |
| 21.559° | |
| Argument of periapsis | 308.491° |
| Last perihelion | 27 September 2024 |
| TJupiter | –0.583 |
| EarthMOID | 0.27503 AU |
| JupiterMOID | 1.09559 AU |
| Physical characteristics | |
Mean radius | <5.9 ± 0.2 km (3.67 ± 0.12 mi)[5] |
| Mass | 4.3±0.8×1014 kg[5] |
| 0.04 (assumed)[5] | |
| Comet total magnitude (M1) | 6.5[6] |
| Comet nuclear magnitude (M2) | 9.2 ± 0.3 |
| –4.9 (2024 perihelion) | |
Comet Tsuchinshan–ATLAS, also known as theGreat Comet of 2024 and formally designated asC/2023 A3, is anon-periodic comet from theOort cloud discovered by thePurple Mountain Observatory inChina on 9 January 2023 and independently found byATLAS South Africa on 22 February 2023. The comet passedperihelion at a distance of 0.39 AU (58 million km; 36 million mi) on 27 September 2024,[1][4] when it became visible to thenaked eye.[7][8][9] Tsuchinshan–ATLAS peaked its brightest magnitude on 9 October, shortly after passing the Sun, with a magnitude of −4.9 per reported observations at the Comet Observation Database (COBS).[7]
The systematic search performed by theAsteroid Terrestrial-impact Last Alert System detected an asteroidal object with an estimatedmagnitude of 18.1 in images taken on 22 February 2023 using the 0.5 m f/2Schmidt reflector at theSutherland Observatory inSouth Africa, when the comet was about 7.3 AU (1.09 billion km; 680 million mi) from the Sun.[10] After the first orbit calculations, it was noticed that it was the same as an 18.7 magnitude object reported to theMinor Planet Center by thePurple Mountain Observatory (Zijinshan inPinyin,Tsuchinshan inpostal romanization, the latter form being traditional for discoveries from this observatory)[10] which was detected in images taken on 9 January 2023. It had been entered in the objects awaiting confirmation list, but had been removed on 30 January 2023 after no follow up observations were reported and the uncertainty on its predicted position grew to the point that it was consideredlost.[10] Based on the naming conventions for comets, it received the name of both observatories.[10]
The object was subsequentlydetected in older images taken by theZwicky Transient Facility (ZTF) inPalomar Observatory on 22 December 2022, when it had a magnitude of 19.2–19.6. These deeper and better resolved images also revealed it had a very condensedcoma and a small straight tail 10arcseconds in length, indicating it was a comet already active at a distance of 7.9 AU (1.18 billion km) from the Sun.[1][11] More evidence of cometary activity was later reported by Hidetaka Sato, M. Mattiazzo and Cristóvão Jacques.[10]
By January 2024, the comet had brightened to an apparent magnitude of 13.6 and according to Bob King, author inSky & Telescope magazine, was visible through 15-inch telescopes at ×142 magnification.[12] The comet was then moving through the constellations ofLibra andVirgo.[12] By the end of April it had brightened to about magnitude 10 and could be observed through small telescopes, showing a short tail.[13] Thespectrum of the comet on 31 May 2024, when the comet was 2.33 AU (349 million km) from the Sun, indicated strongcyanide emission and that the comet is carbon depleted.[14] The comet had a large dust-to-gas ratio.[15]
In May and June the brightening rate of the comet slowed, with the comet staying between magnitudes 10 and 11, while a dusty tail measuring 5 to 15 arcminutes long was observed visually to extend eastwards.[16] AstronomerZdenek Sekanina suggested that this indicates that the comet nucleus has been fragmenting, with the fragmentation starting in late March, as indicated by an increase in the brightening rate and the subsequent decrease in dust production, the narrow teardrop-shaped dust tail, and non-gravitional changes in the orbit. He predicted that the comet would disintegrate before perihelion.[17] Observations of the comet withTRAPPIST robotic telescope indicate that dust production reached a minimum in May, when the comet was near aphase angle of zero, and started to increase again one month later, while gas production rates increased slowly throughout that period.[15] In mid June the comet entered the constellation ofLeo, in the evening sky. In early July, a faint ion tail measuring about one and half degree in length was observed photographically.[18] After mid July the comet was lost in the Sun's glare until September.[12] In August the comet was observed bySTEREO spacecraft to brighten steadily to an apparent magnitude of 7.[19][20]
The comet was recovered byTerry Lovejoy in the morning twilight on 11 September 2024, when it was located in the constellation of Sextans, at a magnitude of 5.5.[21] The comet was spotted with the naked eye and photographed by astronautMatthew Dominick on board theISS on 20 September, followed by fellow astronautDonald Pettit two days later.[22] The first naked eye observation of the comet from Earth was reported on 23 September, with the comet having an estimated magnitude of 3.3, while its tail was reported to be 2.5 degrees long when it was observed with binoculars.[7]
During the last week of September it was located in the dawn sky, better visible from the Southern Hemisphere, and it was predicted to have brightened to second magnitude. Perihelion took place on 27 September.[12] By 1 October the comet had brightened to magnitude 2[7] and its tail was estimated to be 10–12 degrees long.[23] In early October the comet'sspectrum featured prominentsodium lines but it was depleted in carbon bearing species.[24] After that it moved again inconjunction with the Sun.[12] On 4 October the apparent magnitude was estimated to be 1.3.[25] It is estimated that the comet reached its peak dust production rate of 105 kg/sec-1 during perihelion.[11]
On 7 October the comet entered the field of view of theSOHOCoronagraph,[26] and continued to be visible until 11 October.[27] On 9 October 2024, the comet was 3.5 degrees from the Sun.[28] The comet was seen to brighten to a magnitude of −4.9 on that day,[7] becoming one of the brightest comets of the past century. The total magnitude within 5 arcminutes of the nucleus peaked at −2.9.[25] It was the second brightest comet viewed by SOHO since its launch in 1995, aftercomet McNaught in 2007.[27] No observations of the comet with naked eye in daylight were reported, indicating a peak visual magnitude of −2 to −3, while observations of the comet on 9 October with binoculars indicated an apparent magnitude of −3.[25]
The comet was recovered in the evening sky on 10 October[18] and the next days became visible with the naked eye.[12][29][30] It made itsclosest approach to Earth on 12 October at a distance of 71 million km (44 million mi).[31] On that day the comet was estimated to have an apparent magnitude of 0 and its tail was estimated to be 4 degrees long.[25] The comet after that became dimmer, as it moves away from both the Earth and the Sun, however as the elongation became higher, it was easier to spot, despite the brightening Moon.[18] Earth crossed the orbital plane of the comet on 14 October and as a result ananti-tail was observed.[32][33] On 16 October the tail was estimated to be over 20 degrees long photographically.[25] The comet faded quickly and by 20 October it had dimmed to 4th magnitude,[34] however the tail was reported to be 10 degrees long withaverted vision under dark skies and 17.5 degrees long photographically.[35] By 2 November the comet had faded to below magnitude +6 and was no longer visible with naked eye.[36]
Between 22 and 26 October 2024, the comet was observed with the Échelle spectrograph FLECHAS, which is operated at the 90 cm (35 in) telescope of the observatory of the Friedrich Schiller University Jena. In the recorded spectra of the comet, strong emission lines ofC
2,NH
2, atomic oxygen and sodium were detected in the wavelength range between 500–700 nm. A significant decrease in the strength of the sodium emission lines was observed during the observation period.[37] In further spectra of the comet, which were taken with FLECHAS on 3 November 2024, sodium could no longer be detected in emission.[38]
On 21 October and again on 11 November, the comet was formally dubbed theGreat Comet of 2024 by NASA.[39][40][41][42]
When first discovered, the comet was predicted to reach a total magnitude of +3 during perihelion, assuming anabsolute magnitude (H) of 7 and 2.5n = 8, when it would have a smallsolar elongation.[10] Better visibility was predicted about three weeks after perihelion, in mid-October, when it would be around fourth magnitude.[10] Gideon van Buitenen estimated that the comet would reach a magnitude of 0.9 during perihelion and −0.2 at the time of closest approach to Earth, assumingH = 5.2 and 2.5n = 10, and would benefit from the effects offorward scattering.[43][44]
Revised data from June 2024 suggested that the comet would brighten to an apparent magnitude of 2.2, assumingH = 6 and 2.5n = 7.5, which is the average brightening rate of long-period comets in the inner Solar System. However, the comet was expected to be at least one magnitude brighter due to the effects of forward scattering, which could boost the brightness by several magnitudes around the peak of the effect on 9.8 October 2024.[16] More calculations from early September indicated that accounting for forward scattering, the comet would be brighter than magnitude 0 between 5 and 13 October and peak at over −4 on 9 October, brightening by almost 6 magnitudes due toforward scattering.[45]
The comet has aretrograde orbit, lying at an inclination of 139°. Τhe comet had itsperihelion on 27 September 2024, at a distance of 0.391 AU. Τhe closest approach to Earth was on 12 October 2024, at a distance of 0.47 AU. The comet does not approach close to thegiant planets of theSolar System.[10] The orbit is weakly bound to the Sun before entering the planetary region of the Solar System.[2] Due to planetaryperturbations, the outbound orbit will becomehyperbolic.[2] This weakly hyperbolic trajectory may or may not result in the comet being ejected from the Solar System. It is expected to be 200 AU from the Sun in the year 2237.[46]
| Date and time of closest approach | Earth distance(AU) | Sun distance(AU) | Velocity relative to Earth(km/s) | Velocity relative to Sun(km/s) | Uncertainty region(3-sigma) | Constellation | Moon illumination | Reference |
|---|---|---|---|---|---|---|---|---|
| 2024 October 12, 15:18 ± 15 min | 0.47241 AU (70.672 million km; 43.913 million mi; 183.85 LD) | 0.55619 AU (83.205 million km; 51.701 million mi; 216.45 LD) | 80.5 | 56.5 | ±7,000 km | Virgo | 70% | [47] |
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