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Minor planet is the official term for asteroids and trans-Neptunian objects. They are objects in the solar system that orbit the Sun like planets, but which are smaller than planets and not counted among them. If a minor planet produces coma it is called a comet (though conversely not all comets are classified as minor planets). The largest minor planets are also called planetoids.1 Minor planet groups and families
Minor planets are divided into groups and families based on their orbital characteristics.
It is customary to name a group of asteroids after the first member of that group to be discovered (generally the largest).
Groups are relatively loose dynamical associations, whereas families are much "tighter" and result most probably from the catastrophic breakup of a large parent asteroid sometime in the past. They were first recognised by Kiyotsugu Hirayama in 1918 and are often called Hirayama families in his honour. The only prominent families are:
- Eos asteroid s have a semi-major axis between 2.99 AU and 3.03 AU, an eccentricity between 0.01 and 0.13, and an inclination between 8° and 12°. Named after 221 Eos , ~480 members known.
- Themis asteroid s have a semi-major axis between 3.08 AU and 3.24 AU, an eccentricity between 0.09 and 0.22, and an inclination less than 3°. Named after 24 Themis, ~535 members known.
- Koronis asteroid s have a semi-major axis between 2.83 AU and 2.91 AU, an eccentricity less than 0.11, and an inclination less than 3.5°. Named after 158 Koronis, ~310 members known.
- Eunomia asteroids (semi-major axis = 2.5 < a < 2.75 AU, eccentricity = 0.1 < e < 0.2, inclination = 13° < i < 20°), named after 15 Eunomia15 Eunomia ("you KNOW mee uh") is the 12th largest Main belt asteroid. It is also the largest member of the Eunomia family of asteroids. Like other true members of the family, it is composed of silicates and nickel- iron. It is light in colour. It was dis, ~370 members known.
- Flora asteroid s have a semi-major axis between 2.1 AU and 2.3 AU with an inclination of less than 11°. Named after 8 Flora8 Flora ("FLOR uh") is a large, bright Main belt asteroid. It is probably a mixture of silicate rock and nickel- iron metals. It is the largest member of the Flora asteroid family, a remnant of a larger parent body that shattered in a violent collision., ~590 members known. Also called the Ariadne asteroid s after 43 Ariadne43 Ariadne ("AIR ee ADD nee") is a fairly large and bright main belt asteroid. It is also a member of the Flora asteroid family It was discovered by N. Pogson on April 15, 1857 and named after the Greek heroine Ariadne. For reasons unknown, "ASTEROID 43 A.
- Nysa asteroid s have a semi-major axis between 2.41 AU and 2.5 AU, an eccentricity between 0.12 and 0.21, and an inclination between 1.5° and 4.3°. Named after 44 Nysa44 Nysa ("NYE suh") is a quite large and very bright main belt asteroid. It is also the brightest member of the Nysa asteroid family. It is classified as a rare class E asteroid. It was discovered by H. Goldschmidt on May 27, 1857 and named after the myth, ~375 members known. Also called the Hertha asteroid s after 135 Hertha135 Hertha is a metal-rich, quite large main belt asteroid. It orbits among the Nysa asteroid family. Lightcurve data from Hertha indicates a flattened body. Hertha was discovered by C. Peters on February 18, 1874. One occultation of a star by the asteroi.
- Maria asteroid s have a semi-major axis between 2.5 AU and 2.706 AU and an inclination between 12° and 17°. Named after 170 Maria170 Maria is a bright-colored Main belt asteroid. It is probably a mixture silicate rocks and metallic iron- nickel. The Maria asteroid family is named after it. It was discovered by J. Perrotin on January 10, 1877. It orbit was computed by Antonio Abetti, ~80 members known.
Other families have been identified using a variety of techniques, most prominently the Hierarchical Clustering Method (HCM) and the Wavelet Analysis Method (WAM):
- Vesta asteroid s are fragments of 4 Vesta4 Vesta ("VESS tuh") is the third-largest asteroid in the Main belt, between 530 and 468 km in diameter. This and the unusually bright surface make Vesta the brightest asteroid. It is the only asteroid sometimes visible to the naked eye. Vesta was discove's parent body, ~235 members.
- Erigone asteroid s, anmed after 163 Erigone163 Erigone is a dark-colored, fairly big Main belt asteroid and a member of the Erigone family of asteroids. It was discovered by J. Perrotin on April 26, 1876 and named after one of the two Erigones in Greek mythology. Main Belt asteroids., ~45 members.
- Ceres asteroid s, also known as Minerva asteroid s, named after 1 Ceres or 93 Minerva, ~88 members.
- Dora asteroid s, named after 668 Dora , ~78 members.
- Adeona asteroid s, named after 145 Adeona, ~65 members.
- Merxia asteroid s, named after 808 Merxia , ~25-30 members.
- Misa asteroid s, named after 569 Misa , ~26 members.
- Chloris asteroid s, named after 410 Chloris , ~24 members.
- Rafita asteroid s, named after 1644 Rafita , ~22 members.
- Astrid asteroid s, named after 1128 Astrid , ~10 members.
- Meliboea asteroid s, named after 137 Meliboea, ~15 members.
- Naëma asteroid s, named after 845 Naëma , 6 or 7 members.
- Massalia asteroid s, named after 20 Massalia, ~47 members.
- Lydia asteroid s, named after 110 Lydia, ~38 members.
- Nemesis asteroid s or Concordia asteroid s, named after 128 Nemesis or 58 Concordia, ~29 members.
- Bower asteroid s or Endymion asteroid s, named after 1639 Bower or 342 Endymion , ~10-15 members.
- Hygiea asteroid s, named after 10 Hygiea, ~150 members.
- Veritas asteroid s or Undina asteroid s, named after 490 Veritas or 92 Undina, ~29 members.
- Brasilia asteroid s, named after 293 Brasilia , ~14 members.
- Karin asteroid s are a sub-family of the Koronis family; they number 39, the most prominent being 832 Karin . It is a young family which can be traced back to a break-up occurring 5.8ą0.2 million years ago.
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