 The comet on 13 November 2023 | |
| Discovery[1] | |
|---|---|
| Discovered by | Mount Lemmon Survey |
| Discovery date | 23 April 2023 |
| Designations | |
| CK23H020[1] | |
| Orbital characteristics[2] | |
| Epoch | 7 October 2023 (JD 2460224.5) |
| Observation arc | 292 days |
| Earliestprecovery date | 26 March 2023 |
| Number of observations | 724 |
| Aphelion | 480.2 AU |
| Perihelion | 0.894 AU |
| Semi-major axis | 240.6 AU |
| Eccentricity | 0.9963 |
| Orbital period | 3,731 years |
| Inclination | 113.75° |
| 217.04° | |
| Argument of periapsis | 150.65° |
| Last perihelion | 29 October 2023 |
| TJupiter | –0.450 |
| EarthMOID | 0.036 AU |
| JupiterMOID | 1.411 AU |
| Physical characteristics | |
| Comet total magnitude (M1) | 16.1 |
| 6.0 (2023 apparition) | |
C/2023 H2 (Lemmon) is a non-periodiccomet discovered by theMount Lemmon Survey in images obtained on 23 April 2023.[1] It passed perihelion on 29 October 2023 and on 10 November 2023 approached Earth to a distance of 0.19 AU (28 million km) brightening to an apparent magnitude of 6.
The comet was discovered as an asteroidal object with an apparent magnitude of about 21 by theMount Lemmon Survey in images obtained on 23 April 2023. Consequently,precovery images byPanSTARRS dating from 26 March 2023. Cometary activity was observed on 14 May, when the comet had a coma about 12 arcseconds across.[1][3] The comet reached perihelion on 29 October 2023 and on 10 November 2023 approached Earth to a distance of 0.19 AU (28 million km). On that day the comet moved nine degrees across the sky.[4] The comet brightened far above the expectations up to anapparent magnitude of 6, showing also a weak ion tail.[5]
The close encounter with Earth provided the rare opportunity to measure the composition of an otherwise faint comet. The water production rate was estimated to be(59±7)×1026 mol/s, which is unusually low compared to that measured in otherOort Cloud comets at similar heliocentric distances. The comet had also low production rate forhydroxyl radical and low dust signal.[5] However, C/2023 H2 displays very high mixing ratio with respect to water ofcarbon monoxide (16.3±0.6%), as well as high abundances ofethane,methane,hydrogen cyanide, andmethanol. The hyper-volatile species CO,C2H6, andCH4 probably play an important role in the activity of this comet.[5]
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