Themisto , also known as , is a small prograde

irregular satellite In astronomy, an irregular moon, irregular satellite or irregular natural satellite is a natural satellite following a distant, inclined, and often eccentric and retrograde orbit. They have been captured by their parent planet, unlike regular s ...

Jupiter Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but slightly less than one-thousandth t ...

. It was discovered in 1975, subsequently lost, and rediscovered in 2000.

Discovery and naming

Themisto was first discovered by Charles T. Kowal and

Elizabeth Roemer Elizabeth "Pat" Roemer (September 4, 1929April 8, 2016) was an American astronomer and educator who specialized in astronomy with a particular focus on comets and minor planets. She was well-known for the recovery of lost comets, as well as for h ...

on 30 September 1975, reported on 3 October 1975, and designated '. However, not enough observations were made to establish an orbit and it was subsequently lost. Themisto appeared as a footnote in astronomy textbooks into the 1980s. Then, in 2000, a seemingly new satellite was discovered by

Scott S. Sheppard Scott Sander Sheppard (born 1977) is an American astronomer and a discoverer of numerous moons, comets and minor planets in the outer Solar System. He is an astronomer in the Department of Terrestrial Magnetism at the Carnegie Institution for Scie ...

David C. Jewitt David Clifford Jewitt (born 1958) is a British-American astronomer who studies the Solar System, especially its minor bodies. He is based at the University of California, Los Angeles, where he is a Member of the Institute for Geophysics and Pl ...

, Yanga R. Fernández and Eugene A. Magnier, and was designated '. It was soon confirmed that this was the same as the one observed in 1975. This observation was immediately correlated with an observation on 6 August 2000, by the team of

Brett J. Gladman Brett James Gladman (born April 19, 1966) is a Canadian astronomer and a full professor at the University of British Columbia's Department of Physics and Astronomy in Vancouver, British Columbia. He holds the Canada Research Chair in planetary as ...

, John J. Kavelaars,

Jean-Marc Petit This is a list of minor-planet discoverers credited by the Minor Planet Center with the discovery of one or several minor planets (such as near-Earth and main-belt asteroids, Jupiter trojans and distant objects). , the discovery of 612,011 nu ...

Hans Scholl Hans Fritz Scholl (; 22 September 1918 – 22 February 1943) was, along with Alexander Schmorell, one of the two founding members of the White Rose resistance movement in Nazi Germany. The principal author of the resistance movement's ...

Matthew J. Holman Matthew J. Holman (born 1967) is a Smithsonian Astrophysical Observatory, Smithsonian astrophysicist and lecturer at Harvard University. Holman studied at MIT, where he received his bachelor's degree in mathematics in 1989 and his PhD in planetar ...

Brian G. Marsden Brian Geoffrey Marsden (5 August 1937 – 18 November 2010) was a British astronomer and the longtime director of the Minor Planet Center (MPC) at the Center for Astrophysics Harvard & Smithsonian (director emeritus from 2006 to 2010). ...

, Philip D. Nicholson and Joseph A. Burns, which was reported to the Minor Planet Center but not published as an IAU Circular (IAUC). In October 2002 it was officially named after

Themisto In Greek mythology, Themisto (; Ancient Greek: Θεμιστώ) was a Ancient Thessaly, Thessalin princess as the daughter of King Hypseus of LapithsBibliotheca (Pseudo-Apollodorus), Apollodorus, 1.9.2 and the naiad Chlidanope. Her name is derived ...

, daughter of the river god

Inachus In Greek mythology, Inachus, Inachos or Inakhos ( Ancient Greek: Ἴναχος) was the first king of Argos after whom a river was called Inachus River,Apollodorus2.1.1/ref> that drains the western margin of the Argive plain. Biography Fo ...

and lover of

Zeus Zeus or , , ; grc, Δῐός, ''Diós'', label= genitive Boeotian Aeolic and Laconian grc-dor, Δεύς, Deús ; grc, Δέος, ''Déos'', label= genitive el, Δίας, ''Días'' () is the sky and thunder god in ancient Greek reli ...

(Jupiter) in

Greek mythology A major branch of classical mythology, Greek mythology is the body of myths originally told by the ancient Greeks, and a genre of Ancient Greek folklore. These stories concern the origin and nature of the world, the lives and activities ...

Characteristics

Themisto's orbit is unusual: unlike most of

Jupiter's moons There are 82 known moons of Jupiter, not counting a number of moonlets likely shed from the inner moons. All together, they form a satellite system which is called the Jovian system. The most massive of the moons are the four Galilean moons: ...

, which orbit in distinct groups, Themisto orbits alone. The moon is located midway between the Galilean moons and the first group of prograde irregular moons, called the Himalia group. Themisto is about 8 kilometers (5 miles) in diameter (assuming an

albedo Albedo (; ) is the measure of the diffuse reflection of solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body that refl ...

of 0.04). That figure can be used to find a surface area of between 200 and 380 square kilometers.

References

* *

External links

David Jewitt's pages

(by

) {{DEFAULTSORT:Themisto (Moon) Moons of Jupiter Irregular satellites Discoveries by Charles T. Kowal Discoveries by Elizabeth P. Roemer Discoveries by Scott S. Sheppard Discoveries by David C. Jewitt Discoveries by Yanga R. Fernandez Discoveries by Eugene A. Magnier 19750930 20001121 Moons with a prograde orbit