73P/Schwassmann–Wachmann

73P/Schwassmann–Wachmann, also known as Schwassmann–Wachmann 3 or SW3 for short, is a periodic comet that has a 5.4 year orbital period and that has been actively disintegrating since 1995. When it came to perihelion (closest approach to the Sun) in March 2017, fragment 73P-BT was separating from the main fragment 73P-C. Fragments 73P-BU and 73P-BV were detected in July 2022. The main comet came to perihelion on 25 August 2022, when the comet was 0.97 AU from the Sun and 1 AU from Earth. It will be less than 80 degrees from the Sun from 25 May 2022 until August 2023. On 3 April 2025 it will make a modest approach of 0.3 AU to Jupiter. 73P will next come to perihelion on 23 December 2027 when it will be 0.92 AU from the Sun and on the far side of the Sun 1.9 AU from Earth.

Comet Schwassmann–Wachmann 3 was one of the comets discovered by astronomers Arnold Schwassmann and Arno Arthur Wachmann, working at the Hamburg Observatory in Bergedorf, Germany. It began disintegrating on its re-entry to the inner Solar System in 1995, in a reaction triggered by the Sun's heating of the comet as it emerged from the colder regions of the outer Solar System.

Comet 73P/Schwassmann–Wachmann is a parent body of meteor shower Tau Herculids and the 1995 break-up of the comet generated a modest meteor shower around 31 May 2022 4:00-5:00 UT that lasted a few hours.

The comet was discovered as astronomers were exposing photographic plates in search of minor planets for a minor planet survey, on May 2, 1930. On 31 May 1930 the comet passed about 0.062 AU (9.3 million km; 5.8 million mi) from Earth. The comet was lost after its 1930 apparition as the 1935 apparition had poor viewing geometry, but was recovered in 1979. During perihelion in 1985, the comet was unobserved as it was on the far side of the Sun 1.9 AU from Earth. In 1990 the comet reached apparent magnitude 9 and was the best appearance since 1930. On 12 May 2006 the comet passed 0.0783 AU (11.71 million km; 7.28 million mi) from Earth. During the 2011 perihelion passage the primary component 73P-C was recovered on 28 November 2010 near apparent magnitude 21.3; it came to perihelion on 16 October 2011.

Schwassmann–Wachmann has an orbital period of 5.4 years and has an Earth-MOID of 0.014 AU (2.1 million km; 1.3 million mi). At aphelion (farthest distance from the Sun) the comet often makes approaches to Jupiter as it did in 1965 and will in 2167. Schwassmann–Wachmann was originally estimated to have a pre-breakup nucleus diameter of approximately 2.2 km. In 2005 fragment C was estimated to be about 1 km in diameter.