In astronomy, a double planet is a binary satellite system where both objects are planets, or planetary-mass objects, and whose joint barycenter is external to both planetary bodies.
A natural satellite is, in the most common usage, an astronomical body that orbits a planet, dwarf planet, or small Solar System body. Natural satellites are colloquially referred to as moons, a derivation from the Moon of Earth.
A minor-planet moon is an astronomical object that orbits a minor planet as its natural satellite. As of January 2022, there are 457 minor planets known or suspected to have moons. Discoveries of minor-planet moons are important because the determination of their orbits provides estimates on the mass and density of the primary, allowing insights into their physical properties that are generally not otherwise accessible.
90 Antiope is a double asteroid in the outer asteroid belt. It was discovered on 1 October 1866, by Robert Luther. In 2000, it was found to consist of two almost-equally-sized bodies orbiting each other. At average diameters of about 88 km and 84 km, both components are among the 500 largest asteroids. Antiope is a member of the Themis family of asteroids that share similar orbital elements.
45 Eugenia is a large asteroid of the asteroid belt. It is famed as one of the first asteroids to be found to have a moon orbiting it. It was also the second triple asteroid to be discovered, after 87 Sylvia.
216 Kleopatra is a large M-type asteroid with a mean diameter of 120 kilometers and is noted for its elongate bone or dumbbell shape. It was discovered on 10 April 1880 by Austrian astronomer Johann Palisa at the Austrian Naval Pola Observatory, in what is now Pula, Croatia, and was named after Cleopatra, the famous Egyptian queen. It has two small minor-planet moons which were discovered in 2008 and later named Alexhelios and Cleoselene.
22 Kalliope is a large M-type asteroid from the asteroid belt discovered by J. R. Hind on 16 November 1852. It is named after Calliope, the Greek Muse of epic poetry. It is orbited by a small moon named Linus.
The Yarkovsky–O'Keefe–Radzievskii–Paddack effect, or YORP effect for short, changes the rotation state of a small astronomical body – that is, the body's spin rate and the obliquity of its pole(s) – due to the scattering of solar radiation off its surface and the emission of its own thermal radiation.
70 Ophiuchi is a binary star system located 16.6 light years away from the Earth. It is in the constellation Ophiuchus. At magnitude 4 it appears as a dim star visible to the unaided eye away from city lights.
Jean-Luc Margot is a Belgian-born astronomer and a UCLA professor with expertise in planetary sciences and SETI.
47171 Lempo, or as a binary (47171) Lempo–Hiisi (provisional designation 1999 TC36), is a trans-Neptunian object and trinary system from the Kuiper belt, located in the outermost regions of the Solar System. It was discovered on 1 October 1999, by American astronomers Eric Rubenstein and Louis-Gregory Strolger during an observing run at Kitt Peak National Observatory in Arizona, United States. Rubenstein was searching images taken by Strolger as part of their Nearby Galaxies Supernova Search project. It is classified as a plutino with a 2:3 mean-motion resonance with Neptune and is among the brighter TNOs. It reached perihelion in July 2015. This minor planet was named after Lempo from Finnish mythology.
3749 Balam is a stony Flora asteroid and rare trinary system orbiting in the inner regions of asteroid belt. It also forms a secured asteroid pair with sub-kilometer sized asteroid (312497) 2009 BR60. Balam was discovered on 24 January 1982, by American astronomer Edward Bowell at Lowell's Anderson Mesa Station near Flagstaff, Arizona, and received the prov. designation 1982 BG1. It was named after Canadian astronomer David Balam. Balam measures approximately 4.1 kilometers (2.5 miles) in diameter. Its two minor-planet moons have an estimated diameter of 1.66 and 1.84 kilometers, respectively.
Linus, formal designation (22) Kalliope I Linus, is an asteroid moon that orbits the large M-type asteroid 22 Kalliope. It was discovered on August 29, 2001, by astronomers Jean-Luc Margot and Michael E. Brown with the Keck telescope, in Hawaii. Another team also detected the moon with the Canada-France-Hawaii Telescope on September 2, 2001. Both telescopes are on Mauna Kea. It received the provisional designation S/2001 (22) 1, until it was named. The naming proposal appeared in the discovery paper and was approved by the International Astronomical Union in July 2003. Although the naming proposal referred to the mythological Linus, son of the muse Calliope and the inventor of melody and rhythm, the name was also meant to honor Linus Torvalds, inventor of the Linux operating system kernel, and Linus van Pelt, a character in the Peanuts comic strip.
A contact binary is a small Solar System body, such as a minor planet or comet, that is composed of two bodies that have gravitated toward each other until they touch, resulting in a bilobated, peanut-like overall shape. Contact binaries are distinct from true binary systems such as binary asteroids where both components are separated. The term is also used for stellar contact binaries.
(185851) 2000 DP107 is a sub-kilometer sized asteroid, classified as potentially hazardous asteroid and near-Earth object of the Apollo group that is notable because it provided evidence for binary asteroids in the near-Earth population. The PROCYON probe developed by JAXA and the University of Tokyo was intended to flyby this asteroid before its ion thruster failed and could not be restarted.
(35107) 1991 VH is a binary near-Earth asteroid and potentially hazardous asteroid of the Apollo group. It was discovered on 9 November 1991, by Australian astronomer Robert McNaught at Siding Spring Observatory. This binary system is composed of a roughly-spheroidal primary body about one kilometre in diameter, and an elongated natural satellite less than half a kilometre in diameter. The 1991 VH system is unusual for its dynamically excited state; the satellite has a tumbling, non-synchronous rotation that chaotically exchanges energy and angular momentum with its precessing, eccentric orbit. This asteroid system was one of the two targets of NASA's upcoming Janus Mayhem mission, until the delay of the rocket launch made both targets inaccessible.
HD 106515 is a binary star in the constellation of Virgo.
68 Cygni is the Flamsteed designation for a star in the constellation Cygnus. Located approximately 690 parsecs (2,300 ly) distant, the star is a hot blue giant of spectral type O7.5IIIn( ), a massive star that is likely currently expanding to become a supergiant. The star is surrounded by a ring-shaped nebula named Sharpless 2-119.
(300163) 2006 VW139 (provisional designation 2006 VW139, periodic comet designation 288P/2006 VW139) is a binary active asteroid and main-belt comet from the outer regions of the asteroid belt. The object was discovered by Spacewatch in 2006. Its binary nature was confirmed by the Hubble Space Telescope in September 2016. Both primary and its minor-planet moon are similar in mass and size, making it a true binary system. The components are estimated to measure 1.8 kilometers in diameter, orbiting each other at a wide separation of 104 kilometers every 135 days.
HD 72945 and HD 72946 form a co-moving star system in the northern constellation of Cancer. HD 72945 is a binary star that is dimly visible to the naked eye as a point of light with an apparent visual magnitude of 5.91. At an angular separation of 10.10″ is the fainter companion star HD 72946 at magnitude 7.25. It is being orbited by a brown dwarf. The system as a whole is located at a distance of approximately 84 light years from the Sun based on parallax measurements.
