Asteroid belt

As the asteroid belt, asteroid main belt or the accumulation of asteroids and dwarf planets in the Solar System is called, which is located between the orbits of the planets Mars and Jupiter. The majority of known asteroids and dwarf planets of the solar system is located in this area. There, more than 600,000 such properties are currently recognized.

The total area of the individual orbits is now given as about 2.0 to 3.4 AE; 100 years ago calculated by Johann Palisa with 2.2 to 3.6 AE. The total mass of all the asteroids of the main belt is about 5 percent of the mass of Earth's moon and is the largest of Uranus moon Titania or one-third of Pluto.

Discovery

Due to the Titius - Bode designated as Series empirical formula that has complied with the order of the then known planets, began towards the end of the 18th century with the systematic search for a formula according to the "missing" planet in this area. With his discovery of the later named as (1) Ceres dwarf planet on 1 January 1801, Giuseppe Piazzi believed to have found the planet. But were added gradually more similar discoveries in the following years.

1802 Heinrich Wilhelm Olbers discovered with (2) Pallas, a second object that orbits the sun between Mars and Jupiter. This was followed by the discoveries of ( 3) Juno (1804 ), (4 ) Vesta ( 1807) and 38 years later, the (5) Astraea (1845 ). Although it was recognized that all objects between Mars and Jupiter were smaller than the classical planets by orders of magnitude, they were at that time considered as full-fledged planets. So it was that the planet Neptune was counted as three tenth planet in its discovery in 1846.

With the discovery of ( 6) lifting in 1847 set up a flood of new discoveries of asteroids. Therefore, the number of ( major ) planet was on the recommendation of Alexander von Humboldt in 1851, limited to eight and the new object class of asteroids (also called asteroids or minor planets ) created.

By 1890, already 300 asteroids in this " planet gap" were known - until today there are over 400,000 objects; including those such as ( 243) Ida and her companion Dactyl, which have their own small moon.

As part of the redefinition of the term planet by the IAU on August 24, 2006, the largest, nearly spherical asteroid ( 1) Ceres, which has a planet-like structure has been upgraded to the new object classified as a dwarf planet. Pluto was discovered in 1930 it was downgraded in its orbit from the ninth planet because of the presence of comparable properties to dwarf planet.

Formation

It is now generally assumed that the asteroid belt has emerged simultaneously with the rest of the solar system from a pre-solar nebula, and due to the action of Jupiter could not coalesce into a planet. A popular theory in the past, after it in the appropriate place once a small planet - called Phaeton - gave, but was torn by a collision with a large asteroid into pieces, now hardly represented.

Objects

It is in the asteroid around objects in the size of small, irregularly shaped chunks up to the dwarf planet in the main belt, Ceres, with a diameter of about 945 km corresponds to more than a quarter of the diameter of the moon, but only 1.6 percent of its mass has what the relationship between moon and earth comes close. Except for the brightest member belt, Vesta, they are impossible to tell from the Earth with the naked eye.

The composition of the asteroid is not the entire main belt the same. In the inner region ( between 2.0 and 2.5 AU) are dominated by bright objects of spectral types E ( albedo ~ 0.4 ) and S (albedo ~ 0.2 ), the V-Class is located there. It involves silicate- rich objects that have been partially or completely melted in the course of its history. From a distance of about 2.5 AU the dark carbonaceous asteroids of spectral type C dominate (albedo ~ 0.05). Their composition differs significantly from the asteroids in the inner region of the main belt: You are likely to be born of a mixture of ice and rock, which was only moderately heated. In the outer region of the asteroid belt then occurs frequently objects of spectral classes D and P. These are similar to the C- type, but were apparently in their history hardly heated appreciably, so still on its surface ice could be present. With increasing distance from the sun that is a development of objects with complex geological past to primitive ( little modified ) asteroids can be established, nor correspond to the hypothetical planetesimals from the early days of the solar system.

Distribution

The asteroids between Mars and Jupiter are not evenly distributed, because the gravity of the planet Jupiter - caused perturbations - it unites around 70 percent of the total mass of the planets of the solar system in itself. For integer ratios of the orbital periods of the asteroids and Jupiter occur resonances that amplify the gravitational effect. In some of these areas do not form stable asteroid orbits are possible, so here gaps in the main belt occur. After the astronomer Daniel Kirkwood, who had these gaps detected in 1866, they were called Kirkwood gaps.

Note the 4:1 resonance at 2.06 AE, which limits the main belt inward Hestia gap (3:1), 5:2, the resonance region and the Hecuba gap (2:1) which forms the outer boundary of the main belt at 3.3 AU. Located and 2:1 resonance, the vast majority of objects between Mars and Jupiter's orbit, they also have relatively low orbital inclinations - Between the 4:1. Outside this main belt asteroids are occasionally smaller groups that accumulate at resonance fields that exert a stabilizing effect on their orbits.

Vicinity of the main belt ( Distances in AE )

The regions of the main belt asteroids are shown in red, the blue of the smaller asteroids groups.

Asteroid groups in the main belt

Groups of asteroids, the common path elements, such as the length of the semimajor axis, orbital inclination or eccentricity, share and have a similar composition, are called asteroid families. The families formed by the collision and larger objects are made of the resulting fragments. Many asteroids of the main belt can be so in nine major groups divided, each named after the first discovered representative.

Inner Main Belt:

The Flora family is a relatively large group of asteroids of the S-Class in the inner belt ( 2.15 to 2.35 AE). Your tracks have a slope of 1.5 ° to 8 °. Approximately 4-5 % of all main belt asteroids belong to this group.

To Vesta Group includes asteroids with orbital inclinations between 5 ° and 8 ° at a distance from 2.25 to 2.5 AE ( outside the 7:2 resonance ). They mostly belong to the V class. Approximately 6% of all main belt asteroids belong to this family, whose best-known and largest member of the namesake Vesta is.

The Nysa - group is of a similar distance as the Vesta asteroid, but they have their Members orbital inclinations of only 1 ° to 5 °. In the vicinity there are also objects of Massalia group whose orbits only around 0 - 2.5 ° are inclined.

Middle Main Belt:

Another large group was named after the asteroid Eunomia and extends behind the Hestia gap with semi-major axes from 2.5 to 2.8 AU. The objects usually belong to the S-Class and have orbital inclinations between 11 ° and 16 °. With over 4600 members include about 5 % of all main belt asteroids of this family.

The gefion - Family located at distances from 2.7 to 2.8 AU. The orbital inclination of the members who belong mostly to the S- Class is 7.5 ° to 10.5 °. Within the group is the orbit of the dwarf planet Ceres, which, however, does not belong to this family, since its composition differs significantly from that of the other objects.

Outer Main Belt:

The objects of the Koronis group have low orbital inclinations (0 ° - 3.5 ° ) and represent the majority of asteroids that are located at a distance from 2.8 to 2.95 AE, and on which one of the zones, 5:2 - or 7:3 resonance with Jupiter rules, limited. The most famous member of the family is the asteroid (243 ) Ida.

The Eos - group is at a distance from 2.99 to 3.03 AE and has orbital inclinations between 8 ° and 12 °.

The Themis family contains asteroids with semi-major axes in the range of 3.08 and 3.24 AU and orbital inclinations of less than 3 °.

To Hygeia Group has about one percent of the main-belt asteroids. You are at a similar distance as asteroid Themis Group, however, have a higher orbital inclination ( 4 ° - 6 °). The members are mostly objects of the B- and C-Class.

Other occurrences

About ten percent of known asteroids do not run on orbits between Mars and Jupiter.

Within the orbit of Mars to move the Amor -type, Apollo -type and Aten - type asteroids.
On the orbits of the planets Mars, Jupiter and Neptune run asteroids around the sun, called Trojans.
Between Jupiter and Neptune only a few asteroids orbit the Sun, which are called Centaurs.
Beyond Neptune move Trans Neptune and Kuiper belt objects ( KBO - Kuiper Belt Objects). In this area, more objects are assumed to be in the main belt, due to the distance but they are difficult to prove. In addition, can be found at the Trans Neptunes some objects whose diameter is 1000 km, and thus exceed the largest asteroids in the main belt.

Another asteroid belt, the Vulcanoiden is expected to occur within the orbit of Mercury, but so far could not be detected because of the vicinity of the Sun.

Fictions

Asteroid belt provide a dramaturgical element in science fiction films, are in the representation of the object density in all but usually exaggerated. Scenes like the chase in the Star Wars films The Empire Strikes Back or Attack of the Clones show extremely dense fields of fast moving objects, which can only be mastered through pilot art. The date the only realistic representation according to the example of the asteroid belt in our solar system provided the science-fiction film 2001: A Space Odyssey, which contains a scene in which the ship encountered a lonely asteroid.

A space by the main belt usually means low risk, such as the numerous space probes that have crossed him have proved. In fact, consuming course calculations are needed to meet an asteroid, as the large number of more than 600,000 spread over an immense space.

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