The solar system is actually much more complex than it seems, considering all its objects.
A considerable number of small icy objects, similar in size to that of asteroids are in the Kuiper belt and even beyond into the Oort cloud.
The Kuiper Belt invented in 1951 by Gerard Kuiper, extends from the orbit of Neptune to about 30 AU to about 100 AU. They are also called trans-Neptunian objects or "ice dwarf," is the source of short-period comets.
Since the discovery of the first object in 1992, the number of objects discovered in the Kuiper belt has surpassed the thousand and is thought to contain more than 70,000 bodies from more than 100 km in diameter.
By studying the orbits of comets, Ernst Opik, Estonian astronomer, theorized in 1932 that comets come from a "cloud" located in the outer solar system. The idea of Opik was retaken by the Dutch Jan Oort in 1950. Oort said the finding that comets are destroyed gradually by spraying it as and when they move around the Sun.
Oort cloud could be about 50 000 AU, well beyond the Kuiper Belt, and contain many billions of nuclei of comets of more than 1.3 km.
Image: On the picture cons, the Kuiper Belt and Oort Cloud are shown to scale, the small blue spot at center, is the space occupied by the solar system as we used to seen, consisting of its 8 planets.
The Kuiper belt to a diameter very much greater, about 5 to 10 times that of the solar system "classic". The Oort cloud has a diameter 1000 times that of conventional solar system.
This remote region of the solar system and invisible hosts billions of light bodies frozen to limit the attraction of the Sun. That orbit very fragile, almost stationary, comets most distant from the Sun can be affected by any gravitational force, the stars closest to the solar system. The solar system is subjected during its journey through the galaxy, gravitational influences that can disrupt this balance and cause falls of comets in the heart of the system and therefore to the planets. Astronomers estimate that the stellar gravitational perturbations can be very high because some stars pass "near" the Sun. On average, a star passes within 10 000 astronomical units from the Sun every 36 million years and less than 3000 astronomical units, every 400 million years. Edgar Everhart, American astronomer, found that if a comet enters the solar system with an orbital inclination greater than 20 °, it has an even chance of being ejected out of the solar attraction.
The Oort cloud is a remnant of the primitive nebula which collapsed in on itself, there are 5 billion years. After their formation by accretion, all small trans-Neptunian objects, have been influenced by the gas giant planets, pushing them to the periphery of the system. These objects Oort cloud are in a primitive state since their inception, are the materials that formed the solar system at its origin. It is possible that life came from comets is in the era of incessant meteorite bombardment, as they are made of oxygen, carbon, nitrogen, magnesium, silicon, iron...
what up with a little water, organic soup leading to the first living organisms.
Comets were unable to form in the Oort cloud, where they reside today, because at these distances, the material is too sparse to condense.
The only possible place of creation is the planetary system. According to Jan Oort, comets were formed in the asteroid belt (between the orbits of Mars and Jupiter) and ejected by the giant planets during formation of the solar system.
However, the Comets are icy bodies, like a big ball of dirty snow, and the asteroid belt was too hot for ice can condense.
In 1951, a year after the publication of the article Oort, Gerard Kuiper suggested that comets condense farther from the sun, among the giant planets in the belt that bears his name, the Kuiper Belt, it located in the plane the ecliptic beyond the giant planets.
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Image: Halley's comet in 1986, the European spacecraft Giotto was one of the first spacecraft to cross the path of a comet and photograph its nucleus. This comet was Halley's case while it approached the Sun. The data obtained from cameras to Giotto have been restated to obtain the enhanced image of the potato-shaped nucleus of the comet, which measures 15 km in its longest dimension. Some details of dark core surface are visible on the right of the image, while the tail extends to the left.