17 Thetis
17 Thetis is a large main-belt
Asteroid belt
The asteroid belt is the region of the Solar System located roughly between the orbits of the planets Mars and Jupiter. It is occupied by numerous irregularly shaped bodies called asteroids or minor planets...

Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...

. It is an S-type asteroid
S-type asteroid
S-type asteroids are of a stony composition, hence the name. Approximately 17% of asteroids are of this type, making it the second most common after the C-type.-Characteristics:...

, therefore giving it a relatively bright silicate
A silicate is a compound containing a silicon bearing anion. The great majority of silicates are oxides, but hexafluorosilicate and other anions are also included. This article focuses mainly on the Si-O anions. Silicates comprise the majority of the earth's crust, as well as the other...


It was discovered by R. Luther
Karl Theodor Robert Luther
Karl Theodor Robert Luther , normally published as Robert Luther, was a German astronomer who searched for asteroids while working in Düsseldorf....

 on April 17, 1852. It was his first asteroid discovery. Its name comes from Thetis
Silver-footed Thetis , disposer or "placer" , is encountered in Greek mythology mostly as a sea nymph or known as the goddess of water, one of the fifty Nereids, daughters of the ancient one of the seas with shape-shifting abilities who survives in the historical vestiges of most later Greek myths...

, the mother of Achilles
In Greek mythology, Achilles was a Greek hero of the Trojan War, the central character and the greatest warrior of Homer's Iliad.Plato named Achilles the handsomest of the heroes assembled against Troy....

 in Greek mythology
Greek mythology
Greek mythology is the body of myths and legends belonging to the ancient Greeks, concerning their gods and heroes, the nature of the world, and the origins and significance of their own cult and ritual practices. They were a part of religion in ancient Greece...


One Thetidian stellar
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...

An occultation is an event that occurs when one object is hidden by another object that passes between it and the observer. The word is used in astronomy . It can also refer to any situation wherein an object in the foreground blocks from view an object in the background...

 was observed from Oregon
Oregon is a state in the Pacific Northwest region of the United States. It is located on the Pacific coast, with Washington to the north, California to the south, Nevada on the southeast and Idaho to the east. The Columbia and Snake rivers delineate much of Oregon's northern and eastern...

 in 1999. However, the event was not timed.


The mass of Thetis has been calculated from perturbations
Perturbation (astronomy)
Perturbation is a term used in astronomy in connection with descriptions of the complex motion of a massive body which is subject to appreciable gravitational effects from more than one other massive body....

 by 4 Vesta
4 Vesta
Vesta, formally designated 4 Vesta, is one of the largest asteroids, with a mean diameter of about . It was discovered by Heinrich Wilhelm Olbers on March 29, 1807, and is named after the Roman virgin goddess of home and hearth, Vesta....

 and 11 Parthenope
11 Parthenope
11 Parthenope is a large, bright main-belt asteroid.Parthenope was discovered by Annibale de Gasparis on May 11, 1850, the second of his nine asteroid discoveries. It was named after one of the Sirens in Greek mythology, said to have founded the city of Naples...

. In 2007, Baer and Chesley calculated Thetis to have a mass of 1.2 kg with a density of 3.21 g/cm³.

External links

  • Orbital simulation from JPL (Java) / JPL Horizons Ephemeris (displays Elong from Sun and V mag
    Apparent magnitude
    The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...

    for 2011)
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.