NationMaster - Encyclopedia: Themis family

The Themis Asteroid Family is a Hirayama family of asteroids found in the outer portion of the main asteroid belt, between the orbits of Mars and Jupiter. At a mean distance of 3.13 AU (Astronomical Units) from the Sun, it is one of the more populous asteroid families (other families include the Hungaria group, Flora family, Koronis family, and Eos family to name a few). The Themis Asteroid Family consists of a well-defined core of larger asteroids and a surrounding region of smaller ones. This core group includes (and is named after) the asteroid Themis, discovered on April 5, 1853 by Italian astronomer Annibale de Gasparis. An asteroid is a small, solid object in our Solar System, orbiting the Sun. ... The asteroid belt is a region of the solar system falling roughly between the planets Mars and Jupiter where the greatest concentration of asteroid orbits can be found. ... The astronomical unit (AU or au or a. ... The Sun (occasionally referred to as Sol) is the star at the centre of our solar system. ... Themis and Eris: Order and Discord In Greek mythology, Hesiod mentions Themis among the six sons and six daughters—of whom Cronos was one—of Gaia and Ouranos, that is, of Earth with Sky. ... April 5 is the 95th day of the year in the Gregorian calendar (96th in leap years). ... Events January 19 - Giuseppe Verdis opera Il Trovatore premieres in Rome January 21 - Russell L. Hawes patents the envelope folding machine January 29 - Napoleon III marries the Spanish Countess Eugènie at the Tuileries March 4 – Inauguration of US president Franklin Pierce June 7 - Franklin College of Lancaster, Pennsylvania merges... Annibale de Gasparis (April 9, 1819 – March 21, 1892) was an Italian astronomer. ...

Hirayama Families

A Hirayama family of asteroids is a group of minor planets that share similar orbital elements, such as semimajor axis, eccentricity, and orbital inclination. These families are generally thought to have been created through collisions among larger bodies. The Japanese astronomer Kiyotsugu Hirayama first identified these groupings in 1918. (http://www.daviddarling.info/encyclopedia/T/Themis_family.html). Minor planet is the official term for asteroids and trans-Neptunian objects. ... The elements of an orbit are the parameters needed to specify that orbit uniquely, given a model of two ideal masses obeying the Newtonian laws of motion and the inverse-square law of gravitational attraction. ... In geometry, the semi-major axis (also semimajor axis) a applies to ellipses and hyperbolas. ... (This page refers to eccitricity in astrodynamics. ... Inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit and is the angular distance of the orbital plane from the plane of the reference (usually planets equator or the ecliptic), stated in degrees. ... Kiyotsugu Hirayama (平山清次) (1874–1943) was a Japanese astronomer, best known for his discovery that many asteroid orbits were more similar to one another than chance would allow, leading to the concept of asteroid families, now called Hirayama families in his honour. ... 1918 was a common year starting on Tuesday (see link for calendar). ...

Traits of the Themis Family

Asteroids in the Themis family share the following orbital elements:

semimajor axes between 3.08 AU and 3.24 AU
orbital eccentricities between 0.09 and 0.22
orbital inclinations of less than 3°

The Themis family is one of the largest and longest-recognized dynamical families of asteroids, and is made up of C-class asteroids with a composition believed to be similar to that of carbonaceous chondrites (http://www.lpi.usra.edu/meetings/lpsc2004/pdf/1646.pdf). This class of asteroids numerically dominates the asteroid belt as a whole, and its members spectrally appear to be rich in water- and hydroxyl-bearing minerals and have a low albedo (are dark in color). To date, the Themis family is comprised of approximately 535 known asteroids. The major ones include: Some carbonaceous chondrites. ... Hydroxide is a functional group consisting of oxygen and hydrogen: -O−H It has a charge of 1-. The term hydroxyl group is used when the functional group -OH is counted as a substituent of an organic compound. ... This article discusses the physical or planetological property of albedo. ...

24 Themis (thee-mis) is one of the largest Main belt asteroids. ... 62 Erato is a large and dark, probably carbonaceous main belt asteroid. ... 90 Antiope is an asteroid discovered on October 1, 1866 by Robert Luther. ... 104 Klymene is a large, dark main belt asteroid. ... 171 Ophelia is a main belt asteroid and a member of the Themis family of asteroids. ...