28P/Neujmin, also known as Neujmin 1, is a large 21-km periodic comet that orbits the Sun once every 18 years. With a perihelion distance (closest approach to the Sun) of 1.6 AU (240 million km), this comet does not get closer than about 0.571 AU (85.4 million km) from Earth.
Orbital and physical characteristics Initial estimates of the size of its nucleus in 2001 is estimated to be 21.4 km (13.3 mi) in diameter with a low albedo of 0.025. A follow-up study in 2003 revised this figure to 19.4 km (12.1 mi). Since 28P has such a large nucleus, it became brighter than the 20th magnitude in early 2019, roughly 2 years before coming to perihelion. When it came to opposition in May 2020, when it was still 3.5 AU (520 million km) from the Sun, it had an apparent magnitude around 16.9. But during the 2021 perihelion passage the comet was on the opposite side of the Sun as the Earth. The comet is not known for bright outbursts of activity. Archival data from the Subaru Telescope in 2021 revealed that while the measured colors of Neujmin 1's nucleus resembles those of D-type asteroids, its surface microstructure likely differs from them.
References
External links 28P/Neujmin at the JPL Small-Body Database 28P/Neujmin at Gary W. Kronk's Cometography 28P/Neujmin at Seiichi Yoshida's website