Asteroid family
An asteroid family is a group of asteroids with similar orbital elements and a predominantly similar mineralogical composition . Asteroid families are likely formed by an impact of one asteroid on another asteroid, moon, or planet . They are therefore also referred to as collision families. In crater families, only one or more craters remain on a collision partner, while in normal families both partners are destroyed and new asteroids form.
discovery
Asteroid families are found by a greater frequency in diagrams of the orbital elements of asteroids. Orbital elements include the length of the semi-major axis , eccentricity , inclination , length of the ascending node, and the argument of the periapsis . With computer-aided methods, derived orbit elements are often used in clustering to avoid the curse of dimensionality . An assignment of an asteroid to a family is not certain despite almost identical orbit elements, since the parameter space is also randomly filled by background objects. If an asteroid of one family belongs to a different class spectroscopically , it is referred to as an interlooper because belonging to the family is doubtful.
The first description of families came from the Japanese astronomer Kiyotsugu Hirayama in 1918. In his honor, the families he discovered are referred to as Hirayama families . More than a hundred asteroid families are known today through automatic surveys , and more are suspected.
Origin and development
Asteroid families are created when an asteroid collides with another planetary body. Both partners can be destroyed or one or more impact craters occur . The families of the Vestian ( (4) Vesta ) and the families around the asteroids around (2) Pallas , (10) Hygiea and (20) Massalia are examples of the latter . In most families, on the other hand, no surviving larger asteroid can be found and in these the original bodies have probably been completely destroyed. After the impact accrete the remains to rubble pile (dt. Debris pile) of different mineralogical composition.
Young families are several thousand years old. The age is determined by recalculating the path elements that lead to a collision point. The maximum detectable age of asteroid families is around two billion years. After that, small changes in the path elements lead to a distribution that can no longer be distinguished from the background. The changes in the orbital elements are caused by close encounters with planetary bodies and the YORP effect .
Ghost families
Asteroid families are referred to as ghost families if they have only a few members, stand out only slightly from the background and have a high dynamic age. An example is a group around the asteroid (918) Itha . The ghost families often show only a limited distribution in the diameter of the members in contrast to normal families. This is attributed to the size-dependent effect of the YORP effect.
literature
- Alexey Rosaev, Eva Plavalova: Chaos in some young asteroid families . In: Astrophysics. Solar and Stellar Astrophysics . 2016, arxiv : 1612.04951v1 (English).
- V. Carruba, D. Nesvorný, S. Aljbaae, RC Domingos, M. Huaman: On the oldest asteroid families in the main belt . In: Astrophysics. Solar and Stellar Astrophysics . 2016, arxiv : 1603.00818v1 (English).
- Federica Spoto, Andrea Milani, Zoran Knezevic: Asteroid family ages . In: Astrophysics. Solar and Stellar Astrophysics . 2015, arxiv : 1504.05461v1 (English).
- D. Nesvorny, M. Broz, V. Carruba: Identification and Dynamical Properties of Asteroid Families . In: Astrophysics. Solar and Stellar Astrophysics . 2015, arxiv : 1502.01628v1 (English).