Comet C/1861 G1 (Thatcher) is a long-period comet with roughly a 422-year orbit that is expected to return around 2283. It was discovered by A. E. Thatcher. It is responsible for the April Lyrid meteor shower. Carl Wilhelm Baeker also independently found this comet. The comet passed about 0.335 AU from the Earth on 5 May 1861 and last came to perihelion on 3 June 1861.
Comet McNaught, also known as the Great Comet of 2007 and given the designation C/2006 P1, is a non-periodic comet discovered on 7 August 2006 by British-Australian astronomer Robert H. McNaught using the Uppsala Southern Schmidt Telescope. It was the brightest comet in over 40 years, and was easily visible to the naked eye for observers in the Southern Hemisphere in January and February 2007.
An interstellar object is an astronomical object in interstellar space that is not gravitationally bound to a star. This term can also be applied to an object that is on an interstellar trajectory but is temporarily passing close to a star, such as certain asteroids and comets. In the latter case, the object may be called an interstellar interloper.
C/2000 W1 (Utsunomiya–Jones) is a long-period comet from the Oort cloud discovered on November 18, 2000, by Syogo Utsunomiya and Albert F. A. L. Jones. The comet reached up to apparent magnitude 5.5, but was only 27 degrees from the Sun in mid-December 2000.
C/1999 F1 (Catalina) is one of the longest known long-period comets. It was discovered on March 23, 1999, by the Catalina Sky Survey. The current perihelion point is outside of the inner Solar System which helps reduce planetary perturbations to this outer Oort cloud object and keep the inbound and outbound orbital periods similar.
(668643) 2012 DR30 is a trans-Neptunian object and centaur from the scattered disk and/or inner Oort cloud, located in the outermost region of the Solar System. The object with a highly eccentric orbit of 0.99 was first observed by astronomers with the Spacewatch program at Steward Observatory on 31 March 2009. It measures approximately 188 kilometers (120 miles) in diameter.
C/2013 US10 (Catalina) is an Oort cloud comet discovered on 31 October 2013 by the Catalina Sky Survey at an apparent magnitude of 19 using a 0.68-meter (27 in) Schmidt–Cassegrain telescope. From September 2015 to February 2016 the comet was around apparent magnitude 6. The comet took around a million years to complete half an orbit from its furthest distance in the Oort cloud and should be ejected from the Solar System over many millions of years.
C/2017 K2 (PanSTARRS) is an Oort cloud comet with an inbound hyperbolic orbit, discovered in May 2017 at a distance beyond the orbit of Saturn when it was 16 AU (2.4 billion km) from the Sun. Precovery images from 2013 were located by July. It had been in the constellation of Draco from July 2007 until August 2020. As of June 2022, the 3-sigma uncertainty in the current distance of the comet from the Sun is ±6000 km.
ʻOumuamua is the first interstellar object detected passing through the Solar System. Formally designated 1I/2017 U1, it was discovered by Robert Weryk using the Pan-STARRS telescope at Haleakalā Observatory, Hawaii, on 19 October 2017, approximately 40 days after it passed its closest point to the Sun on 9 September. When it was first observed, it was about 33 million km from Earth and already heading away from the Sun.
C/2017 U7 (PanSTARRS) is a hyperbolic comet, first observed on 29 October 2017 by astronomers of the Pan-STARRS facility at Haleakala Observatory, Hawaii, United States when the object was 7.8 AU (1.2 billion km) from the Sun. Despite being discovered only 10 days after interstellar asteroid 1I/'Oumuamua, it was not announced until March 2018 as its orbit is not strongly hyperbolic beyond most Oort Cloud comets. Based on the absolute magnitude of 10.6, it may measure tens of kilometers in diameter. As of August 2018, there is only 1 hyperbolic asteroid known, ʻOumuamua, but hundreds of hyperbolic comets are known.
C/2018 C2 (Lemmon) is a hyperbolic comet. It was first observed on 5 February 2018 by the Mount Lemmon Survey conducted at the Mount Lemmon Observatory near Tucson, Arizona, in the United States. The discovery was announced on 4 March 2018 along with another hyperbolic object, A/2017 U7. Based on the absolute magnitude of 15.1, it may measure several kilometers in diameter. On 22 March 2018 it was determined to be a hyperbolic comet.
C/2018 F4 (PanSTARRS) is a hyperbolic comet. It was discovered on 17 March 2018 when it was beyond the orbit of Jupiter, 6.4 AU (960 million km) from the Sun. It was quite far from the Sun and turned out to simply be an asteroidal object that was discovered before cometary activity was noticeable. As perihelion is inside the orbit of Jupiter, this object should become more active. In April 2018 it was determined to be a hyperbolic comet. Given that the incoming velocity was similar to that of an Oort cloud object, we can very confidently say that it is not of interstellar origin. C/2018 F4 fragmented around August 2020.
Comet C/2018 V1 (Machholz–Fujikawa–Iwamoto) is a minor body that follows a slightly hyperbolic orbit. It was visually discovered on 7 November 2018 by Donald Machholz using an 18.5-inch reflecting telescope and it reached perihelion on 3 December 2018.
2I/Borisov, originally designated C/2019 Q4 (Borisov), is the first observed rogue comet and the second observed interstellar interloper after ʻOumuamua. It was discovered by the Crimean amateur astronomer and telescope maker Gennadiy Borisov on 29 August 2019 UTC.
C/2010 U3 (Boattini) is the hyperbolic comet with the longest observation arc and took around a million years to complete half an orbit from its furthest distance in the Oort cloud. It was discovered on 31 October 2010 by Andrea Boattini in images taken with the Mount Lemmon Survey's 1.5-m reflector. The perihelion point is outside of the inner Solar System.
C/2021 O3 (PanSTARRS) is perhaps an Oort cloud comet, discovered on 26 July 2021 by the Pan-STARRS sky survey. It came to perihelion on 21 April 2022 at 0.287 AU (42.9 million km). from the Sun.
2022 NX1 is a near-Earth object roughly 10 meters (33 ft) in diameter discovered by Grzegorz Duszanowicz and Jordi Camarasa. The object orbits the Sun but makes slow close approaches to the Earth–Moon system. Between 11 June 2022 and 3 July 2022 (a period of 22 days) it passed within Earth's Hill sphere (roughly 0.01 AU (1.5 million km; 0.93 million mi)) at a low relative velocity and became temporarily captured by Earth's gravity, with a geocentric orbital eccentricity of less than 1 and negative geocentric orbital energy. Due to its Earth-like orbit, the object might be of artificial origin or lunar ejecta. However, visible spectroscopy obtained with the Gran Telescopio Canarias shows that it is an asteroid. The closest approach to Earth in 2022 was 26 June 2022 at roughly 812,200 km (504,700 mi) when it had a relative velocity of 0.96 km/s (2,100 mph). It was last near Earth around 16 January 1981 when it passed about 600,000 km (370,000 mi) from Earth. It will return as a temporary satellite in December 2051.
C/2023 V5 (Leonard) was discovered on 6 November 2023 by the Catalina Sky Survey. It came to perihelion on 13 December 2023 at 0.849 AU (127.0 million km), from the Sun. It is probably a Liller family comet, together with C/1988 A1 (Liller), C/1996 Q1 (Tabur), C/2015 F3 (SWAN), and C/2019 Y1 (ATLAS).
C/2024 L5 (ATLAS) was discovered on 14 June 2024 as A117uUD by the Asteroid Terrestrial-impact Last Alert System (ATLAS), South Africa, Sutherland. It will reach perihelion on 10 March 2025 at 3.432 AU (513.4 million km), from the Sun. It is the second known Solar System comet that became interstellar after experiencing a planetary encounter. C/1980 E1 (Bowell) reached a hyperbolic trajectory after an encounter with Jupiter on 9 December 1980. C/2024 L5 (ATLAS) experienced a very close encounter at 0.0048 AU with Saturn on 24 January 2022.
