The Themis Asteroid 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.

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).

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:

• 24 Themis
• 62 Erato
• 90 Antiope
• 104 Klymene
• 171 Ophelia
• 468 Lina
• 526 Jena
• 846 Lipperta

See also

• Asteroid 4279 De Gasparis , named in the honor of Annibale de Gasparis.