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Themis (hypothetical moon)
Encyclopedia
On April 28, 1905, William H. Pickering
, who had seven years earlier discovered Phoebe
, announced the discovery of a tenth satellite
of Saturn
, which he promptly named Themis
. The photographic plates on which it supposedly appeared, thirteen in all, spanned a period between April 17 and July 8, 1904. However, no other astronomer has ever confirmed Pickering's claim.
Pickering attempted to compute an orbit, which showed a fairly high inclination
(39.1° to the ecliptic
), fairly large eccentricity (0.23) and a semi-major axis
(1,457,000 km) slightly less than that of Hyperion
. The period was supposedly 20.85 days, with prograde
motion.
Pickering estimated the diameter at 38 miles (61 km), but since he also gave 42 miles (68 km) as the diameter of Phoebe, he was clearly overestimating the albedo
; using the modern figure for Phoebe gives Themis a diameter of 200 km.
Oddly, in April 1861, Hermann Goldschmidt had also believed that he had discovered a new satellite of Saturn between Titan and Hyperion, which he called Chiron
. Chiron also does not exist (however, the name was used much later for the comet
/asteroid
2060 Chiron
).
Pickering was awarded the Lalande Prize
of the French Academy of Sciences
in 1906 for his "discovery of the ninth and tenth satellites of Saturn".
The actual tenth satellite of Saturn (in order of discovery) was Janus
, which was discovered in 1966 and confirmed in 1980. Its orbit is far from the supposed orbit of Themis.
There is also an asteroid named 24 Themis
.
William Henry Pickering
William Henry Pickering was an American astronomer, brother of Edward Charles Pickering. He was elected a Fellow of the American Academy of Arts and Sciences in 1883.-Work:...
, who had seven years earlier discovered Phoebe
Phoebe (moon)
Phoebe is an irregular satellite of Saturn. It was discovered by William Henry Pickering on 17 March 1899 from photographic plates that had been taken starting on 16 August 1898 at the Boyden Observatory near Arequipa, Peru, by DeLisle Stewart...
, announced the discovery of a tenth satellite
Natural satellite
A natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called its primary. The two terms are used synonymously for non-artificial satellites of planets, of dwarf planets, and of minor planets....
of Saturn
Saturn
Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...
, which he promptly named Themis
Themis
Themis is an ancient Greek Titaness. She is described as "of good counsel", and is the embodiment of divine order, law, and custom. Themis means "divine law" rather than human ordinance, literally "that which is put in place", from the verb τίθημι, títhēmi, "to put"...
. The photographic plates on which it supposedly appeared, thirteen in all, spanned a period between April 17 and July 8, 1904. However, no other astronomer has ever confirmed Pickering's claim.
Pickering attempted to compute an orbit, which showed a fairly high inclination
Inclination
Inclination in general is the angle between a reference plane and another plane or axis of direction.-Orbits:The inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit...
(39.1° to the ecliptic
Ecliptic
The ecliptic is the plane of the earth's orbit around the sun. In more accurate terms, it is the intersection of the celestial sphere with the ecliptic plane, which is the geometric plane containing the mean orbit of the Earth around the Sun...
), fairly large eccentricity (0.23) and a semi-major axis
Semi-major axis
The major axis of an ellipse is its longest diameter, a line that runs through the centre and both foci, its ends being at the widest points of the shape...
(1,457,000 km) slightly less than that of Hyperion
Hyperion (moon)
Hyperion , also known as Saturn VII, is a moon of Saturn discovered by William Cranch Bond, George Phillips Bond and William Lassell in 1848. It is distinguished by its irregular shape, its chaotic rotation, and its unexplained sponge-like appearance...
. The period was supposedly 20.85 days, with prograde
Prograde
Prograde can refer to:*Prograde or direct motion, in astronomy, a type of motion of astronomical bodies* Prograde metamorphism, in geology, describes mineral changes in rocks under increasing pressure and/or temperature conditions...
motion.
Pickering estimated the diameter at 38 miles (61 km), but since he also gave 42 miles (68 km) as the diameter of Phoebe, he was clearly overestimating the albedo
Albedo
Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...
; using the modern figure for Phoebe gives Themis a diameter of 200 km.
Chiron (hypothetical moon)
Chiron is the name given to a supposed moon of Saturn sighted by Hermann Goldschmidt in 1861. It has since been determined that no such moon exists....
. Chiron also does not exist (however, the name was used much later for the comet
Comet
A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...
/asteroid
Asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
2060 Chiron
2060 Chiron
2060 Chiron is a minor planet in the outer Solar System. Discovered in 1977 by Charles T. Kowal , it was the first-known member of a new class of objects now known as centaurs, with an orbit between Saturn and Uranus.Although it was initially classified as an asteroid, it was later found to...
).
Pickering was awarded the Lalande Prize
Lalande Prize
The Lalande Prize was an award for scientific advances in astronomy, given from 1802 through 1970 by the French Academy of Sciences.The prize was named for, and endowed by, astronomer Jérôme Lalande in 1801...
of the French Academy of Sciences
French Academy of Sciences
The French Academy of Sciences is a learned society, founded in 1666 by Louis XIV at the suggestion of Jean-Baptiste Colbert, to encourage and protect the spirit of French scientific research...
in 1906 for his "discovery of the ninth and tenth satellites of Saturn".
The actual tenth satellite of Saturn (in order of discovery) was Janus
Janus (moon)
Janus is an inner satellite of Saturn. It is also known as Saturn X . It is named after the mythological Janus.-Discovery and orbit:Janus occupies practically the same orbit as the moon Epimetheus...
, which was discovered in 1966 and confirmed in 1980. Its orbit is far from the supposed orbit of Themis.
There is also an asteroid named 24 Themis
24 Themis
24 Themis is one of the largest main-belt asteroids. It is also the largest member of the Themistian asteroid family. It was discovered by Annibale de Gasparis on April 5, 1853...
.
Themis in fiction
- Philip Latham (pen-name of Robert S. RichardsonRobert S. RichardsonRobert Shirley Richardson was an American astronomer, born in Indiana. He also published science fiction using the pseudonym Philip Latham.-Bibliography:* The Xi Effect, 1950...
), in his novel Missing Men of SaturnMissing Men of SaturnMissing Men of Saturn is a juvenile science fiction novel, published first during 1953, by astronomer and author Robert S. Richardson as with cover illustration by Alex Schomburg. The story concerns Dale Sutton's mission to the dreaded planet Saturn from which no one has ever returned...
, has Themis collide with Titan, "getting rid of the little nuisiance once and for all", according to the introduction. - John VarleyJohn Varley (author)John Herbert Varley is an American science fiction author.-Biography:Varley grew up in Fort Worth, Texas, moved to Port Arthur in 1957, and graduated from Nederland High School. He went to Michigan State University on a National Merit Scholarship because, of the schools that he could afford, it...
's science fictionScience fictionScience fiction is a genre of fiction dealing with imaginary but more or less plausible content such as future settings, futuristic science and technology, space travel, aliens, and paranormal abilities...
novel TitanTitan (John Varley)Titan is a Locus Award winning 1979 science fiction novel by John Varley. It is the first book in his Gaea Trilogy. It was nominated for the Nebula Award for Best Novel in 1979, and the Hugo Award for Best Novel in 1980.-Plot summary:...
is set aboard an expedition to Saturn. As they approach the planet and prepare to enter orbit, the astronomer onboard discovers a new moon. At first she believes she has recovered Pickering's lost moon, so she names it Themis. - Robert Anton Wilson'sRobert Anton WilsonRobert Anton Wilson , known to friends as "Bob", was an American author and polymath who became at various times a novelist, philosopher, psychologist, essayist, editor, playwright, poet, futurist, civil libertarian and self-described agnostic mystic...
novel Schrödinger's Cat trilogySchrödinger's Cat trilogyThe Schrödinger's Cat Trilogy is a trilogy of novels by Robert Anton Wilson consisting of The Universe Next Door, The Trick Top Hat, and The Homing Pigeons, each illustrating a different interpretation of quantum physics...
makes frequent reference to Pickering's Moon as a satellite that revolves the "wrong way" around its primary.