OORT

Jan Hendrik Oort 1900-1992

Jan Hendrik Oort, Dutch astronomer, was born April 28, 1900 in Franeker, The Netherlands. He led his long career at the Observatory of Leiden where he was director from 1945 to 1970.
He was educated at the University of Groningen. It is the student Cornelius Jacobus Kapteyn (1851-1922).
He has conducted extensive research on our Galaxy and has shown that the Sun was about 19 200 light years from the center of our galaxy, the Milky Way, in the direction of the constellation Sagittarius.
In 1924, Oort discovered the galactic halo, a group of stars orbiting the Milky Way, but outside the main disk. In 1927, it highlights the differential rotation of our Galaxy. In 1932, it determines its mass (100 billion times the Sun), by studying the motions of stars and their distribution in space. It shows the spiral structure and estimates the period of rotation of the Milky Way at 200 million years. In 1950, he suggested that comets come from a common region of the solar system, between 40 000 and 100 000 astronomical units. Some of these comets sometimes leave the "cloud" to make an orbit whose plane may be different from that of the ecliptic. The cloud bears his name. In 1959, he was a foreign member of the Royal Society.
From 1958 to 1961 he was president of the International Astronomical Union.
Asteroid 1691 Oort (1956 RB), discovered September 9, 1956 by Ingrid van Houten-Groeneveld and Karl Wilhelm Reinmuth was named in his honor.
Jan Hendrik Oort died November 5, 1992 in Leiden.

Image: Studying the orbits of comets, Ernst Opik, astronomer Estonian hypothesized in 1932 that the long-period comets, come from a region, "cloud" located in the outer solar system.
The idea of Opik was taken over by Dutch Jan Oort in 1950. He made the observation that the orbits of comets are unstable.
They kill slowly by spraying it as and when they pass around the sun, or if they existed since the creation of the solar system, they would be destroyed long ago. We would not know today what a comet.

Oort Cloud

The solar system is actually much more complex than it seems, considering all of its objects. A considerable number of small icy objects of similar size to that of asteroids are in the Kuiper belt and even beyond into the Oort cloud. This remote region of the solar system and invisible hosts hundreds of billions of light bodies frozen to limit the attraction of the Sun.
That orbit very fragile, almost stationary, the most distant comets from the sun can be disrupted by any gravitational force, the stars closest to the solar system. The solar system is subjected during its journey through the galaxy, with gravitational influences that can disrupt this balance and cause falls of comets in the heart of the system and then to the planets.
Astronomers estimate that the stellar perturbations can be very high because some stars near the Sun pass through the Oort cloud. 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, has shown that if a comet enters the solar system with an orbital inclination of 20 °, it has an even chance of being ejected and 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 that would have pushed to the periphery.

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 has come from comets in the era of incessant meteorite bombardment, as they are made of oxygen, carbon, nitrogen, magnesium, silicon, iron... what up with a little water, the leading organic soup in the first living organisms.
Comets could not form in the Oort cloud, where they reside today, because at these distances, the material is too sparse to condense.
The only place possible is the creation of 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 large dirty snowballs and the asteroid belt was too hot for ice can condense.
In 1951, a year after the publication of the article by Oort, Gerard Kuiper suggested that comets condense further from the Sun, among the giant planets in the belt that bears his name, the Kuiper belt, is located in the plane of the ecliptic beyond the giant planets.

Image: The Kuiper Belt and Oort Cloud are shown to scale. The small blue spot in the center is the space occupied by the solar system as we used to see, consists of its eight planets. The Kuiper belt to a diameter very much greater (5-10 times) than the solar system "classic". The Oort cloud has a diameter 1000 times that of conventional solar system.