C/2024 G3 (ATLAS)

For other comets discovered by the Asteroid Terrestrial-impact Last Alert System, see Comet ATLAS.

C/2024 G3 (ATLAS)

Discovery
Discovered by	T. Linder
Discovery site	ATLAS-W68
Discovery date	5 April 2024
Orbital characteristics
Epoch	6 June 2024 (JD 2460467.5)
Observation arc	206 days
Number of observations	271
Perihelion	0.09 AU
Semi-major axis	2,631 AU (inbound) 6,135 AU (outbound)
Eccentricity	0.9999970(Epoch 1 Jan 2022) 1.0000141(Epoch 6 Jun 2024) 0.9999973(Epoch 1 Jan 2028)
Orbital period	135,000 years (inbound) 450,500 years (outbound)
Inclination	116.852°
Longitude of ascending node	220.331°
Argument of periapsis	108.127°
Next perihelion	13 January 2025
Earth MOID	0.4826 AU
Jupiter MOID	3.8373 AU
Comet total magnitude (M1)	8.8
Comet nuclear magnitude (M2)	12.4

C/2024 G3 (ATLAS) is a long-period, sungrazing comet, which will reach perihelion on January 13, 2025, at a distance of 0.09 AU from the Sun. It could become the brightest comet of 2025, possibly exceeding apparent magnitude of –2.0. The comet is visible in the southern hemisphere before and after perihelion. It can only be observed in the daytime sky around perihelion in the northern hemisphere.

Observational history

The comet was discovered by the Asteroid Terrestrial-impact Last Alert System (ATLAS) survey on April 5, 2024. The comet at the time was a magnitude 19 object about 4.38 AU (655 million km) from Earth. Futher observations indicated it had a diffuse coma about 4.5 arcseconds across and a straight tail. At the time of discovery, it was assumed that this was a new comet from the Oort cloud, and with its very weak absolute magnitude (H=9), there was very little to no chance that it would survive perihelion. But as the orbit was refined it was reclassified as a periodic comet. This was also indicated by the brightness dynamics exhibited by the comet.

By 30 October 2024, the comet had an apparent magnitude of 11.9 per reported observations at the Comet Observation Database (COBS), visible with large telescopes. Typically, new long-period comets from the Oort cloud increase their brightness much slower compared to other comets, typically when they are closer to the sun than 3-4 AU, assuming 2.5n=~8. Nearing perihelion, the comet magnitude could be enhanced by forward scattering and become as bright as -2.1 magnitude, possibly making it the 3rd brightest comet in 20 years, although comets such as Comet McNaught and C/2023 A3 (Tsuchinshan-ATLAS) have had higher peak magnitudes.