Small body of the solar system – Wikipedia

Place of small bodies of the solar system in the classification of objects of the solar system.

In astronomy, a Small body of the solar system is a celestial object of the solar system orbiting around the sun and which is neither a planet, nor a dwarf planet, nor a satellite.

The term was adopted in 2006 by the International Astronomical Union (UAI) in order to clarify the classification of objects revolving around the sun. Small bodies mainly include asteroids that circulate inside Neptune orbit, transneptunian objects of which all or part of the orbit is beyond this orbit, and the comets which are characterized by a emission of gas and dust on part of the orbit.

The International Astronomical Union (UAI), an organization responsible for astronomical nomenclature, defines a small body as a celestial body of the solar system which satisfies the following conditions ^{[ first ]} :

• it is in orbit around the sun;
• There is neither a planet, nor a dwarf planet, that is to say that he does not have sufficient mass for his own gravity to prevail over the cohesion forces of the solid body and the maintenance in balance hydrostatic (in an almost spherical form). First , although the definition by exclusion does not impose this constraint, such an object does not have, like the dwarf planets, clearly gives way in its orbital vicinity.

This term was adopted the August 24, 2006 by the international astronomical union ^{[ first ]} . He participates in a classification of solar system objects in three categories according to their size and environment.

Orbit [ modifier | Modifier and code ]

The definition of the UAI only concerns objects directly in orbit around the sun. It therefore does not apply to natural satellites of planets, dwarf planets or even other small bodies.

On the other hand, this definition does not explain the status of binary objects of which each member is of comparable size and orbit around the other, the whole system orbiting around the sun. Several objects of this type are known, for example the asteroid (90) antiope.

Dimensions [ modifier | Modifier and code ]

The definition of the UAI does not specify any size of size, both lower and upper.

The upper and lower limits in size and in mass of dwarf planets are not specified in the Resolution 5A of the international astronomical union.

The upper limit is determined by the concept of “hydrostatic balance”, but the dimensions to which an object reaches such a state are not determined; Empirical observations suggest that they vary according to the composition and history of the object. The initial version of the Resolution 5 defined the hydrostatic balance as applying “to objects whose mass exceeds 5 × 10 ²⁰ kg (or 500 million billion tonnes) and the diameter 800 km » ^{[ 2 ]} , but this was not retained in the final resolution.

As a comparison, among the natural satellites of the giant planets, a body as large as Prote, Neptune satellite measuring more than 400 km In medium diameter, does not have a spherical shape. On the other hand, Mimas, Saturn satellite of a comparable size, is clearly spherical.

No lower limit is specified. The smallest macroscopic objects in orbit around the sun are named meteoroids. Below this size, there are interplanetary dust, molecules and simple atoms. It is not specified if the small bodies bring together all of these objects.

Neighborhood [ modifier | Modifier and code ]

The definition of a small body calls on that of a planet and a dwarf planet and assumes that it does not “make room clear in its vicinity”, but does not explain this concept more.

Alan Stern and Harold F. Levison defined a criterion to distinguish between a planet and a dwarf planet ^{[ 3 ]} , expressing the probability of a meeting between an object and a smaller body following a deviation from the latter’s orbit. According to its authors, this criterion makes it possible to estimate the ability of a body to clean its neighborhood. Stern and Levison found a gap of five orders of magnitude between its value for Mars and that of the greatest asteroids and transneptunians. Using this work, Steven Soter proposed a parameter called planetary discriminating, making it possible to distinguish between dwarf planets and the eight planets of the solar system, on the basis of their ability to clean the smaller bodies by collision, capture or disturbance gravitational ^{[ 4 ]} . These criteria could A stronger apply to small bodies.

There is no official definition of the different categories of small bodies. The use is to call asteroids the small bodies whose orbit is entirely inside that of Neptune, transneptunian objects (or objects of kuiper) those which circulate in all or part beyond this orbit and comets Small bodies that emit gases or dust on part of their orbit.

The orbits of the vast majority of small bodies in the solar system are located in two distinct regions, the asteroid belt located between the orbits of the planets Mars and Jupiter and the Kuiper belt located beyond the orbit of Neptune between 50 and 100 astronomical sun units. Other regions contain lower concentrations of small bodies, such as geocroisters asteroids whose trajectory cuts the orbit of the earth, the centaurs which circulate between Jupiter and Neptune, comets or scattered objects. To explain the origin of the comets at a long period, astronomers hypothesized that there was a large reservoir of small bodies, the Oort cloud, which would extend beyond the Kuiper belt and until 100,000 astronomical sun units ^{[ 5 ]} .

Bibliography [ modifier | Modifier and code ]

Related articles [ modifier | Modifier and code ]

• Other types of body defined by the UAI:

External link [ modifier | Modifier and code ]