From Wikipedia, the free encyclopedia
A
Hirayama family
of
asteroids
is a group of
minor planets
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
Japanese
astronomer
Kiyotsugu Hirayama
(1874?1943) pioneered the estimation of proper elements for asteroids, and first identified several of the most prominent families in 1918.
[1]
[2]
Kiyotsugu Hirayama initially identified the
Koronis
,
Eos
, and
Themis
families,
[1]
and later recognized also the
Flora
and
Maria
families. For a list of known families, see
Asteroid family § All families
.
References
[
edit
]