Hirayama families
Encyclopedia
A Hirayama family of asteroid
s is a group of minor planet
s that share similar orbital elements
, such as semimajor axis, eccentricity, and orbital inclination
. The members of the families are thought to be fragments of past asteroid collisions.
Strictly speaking, families and their membership are identified by analysing the so-called proper orbital elements
rather than the current osculating
orbital elements
, which regularly fluctuate on timescales of tens of thousands of years. The proper elements are related constants of motion that are thought to remain almost constant for times of at least tens of millions of years.
The Japan
ese astronomer
Kiyotsugu Hirayama
(1874-1943) pioneered the estimation of proper elements for asteroids, and first identified several of the most prominent families in 1918 http://www.daviddarling.info/encyclopedia/H/Hirayama_family.html.
Kiyotsugu Hirayama initially identified the Koronis
, Eos
, and Themis
families, and later recognized also the Flora
and Maria families.
A list of the recognized families can be found here
.
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...
s is a group of minor planet
Minor planet
An asteroid group or minor-planet group is a population of minor planets that have a share broadly similar orbits. Members are generally unrelated to each other, unlike in an asteroid family, which often results from the break-up of a single asteroid...
s that share similar orbital elements
Orbital elements
Orbital elements are the parameters required to uniquely identify a specific orbit. In celestial mechanics these elements are generally considered in classical two-body systems, where a Kepler orbit is used...
, such as semimajor axis, eccentricity, and orbital 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...
. The members of the families are thought to be fragments of past asteroid collisions.
Strictly speaking, families and their membership are identified by analysing the so-called proper orbital elements
Proper orbital elements
The proper orbital elements of an orbit are constants of motion of an object in space that remain practically unchanged over an astronomically long timescale...
rather than the current osculating
Osculating orbit
In astronomy, and in particular in astrodynamics, the osculating orbit of an object in space is the gravitational Kepler orbit In astronomy, and in particular in astrodynamics, the osculating orbit of an object in space (at a given moment of time) is the gravitational Kepler orbit In astronomy,...
orbital elements
Orbital elements
Orbital elements are the parameters required to uniquely identify a specific orbit. In celestial mechanics these elements are generally considered in classical two-body systems, where a Kepler orbit is used...
, which regularly fluctuate on timescales of tens of thousands of years. The proper elements are related constants of motion that are thought to remain almost constant for times of at least tens of millions of years.
The Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
ese astronomer
Astronomer
An astronomer is a scientist who studies celestial bodies such as planets, stars and galaxies.Historically, astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences between them using...
Kiyotsugu Hirayama
Kiyotsugu Hirayama
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....
(1874-1943) pioneered the estimation of proper elements for asteroids, and first identified several of the most prominent families in 1918 http://www.daviddarling.info/encyclopedia/H/Hirayama_family.html.
Kiyotsugu Hirayama initially identified the Koronis
Koronis family
]The Koronis family is a family of asteroids in the main belt between Mars and Jupiter. They are thought to have been formed at least two billion years ago in a catastrophic collision between two larger bodies. The largest known is about in diameter. The Koronis family travels in a cluster along...
, Eos
Eos family
The Eos or Eoan family is a prominent family of main belt asteroids that is believed to have formed as a result of an ancient catastrophic collision. Members of the family share similar orbits. The family is named after 221 Eos....
, and Themis
Themis family
The Themis or Themistian 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 from the Sun, it is one of the more populous asteroid families...
families, and later recognized also the Flora
Flora family
The Flora family of asteroids is a large grouping of S-type asteroids in the inner main belt, whose origin and properties are relatively poorly understood at present...
and Maria families.
A list of the recognized families can be found here
Asteroid family
An asteroid family is a population of asteroids that share similar proper orbital elements, such as semimajor axis, eccentricity, and orbital inclination. The members of the families are thought to be fragments of past asteroid collisions...
.