The Oort cloud is a theoretical cloud of predominantly icy planetesimals proposed to surround the Sun. It is divided into two regions: a disc-shaped inner OortCloud and a spherical outer Oortcloud. The outer limit of the Oort Cloud defines the cosmographic boundary of the Solar System and the extent of the Sun’s Hill sphere. It may be the source of all long-period and Halley-type comets entering the inner Solar System.
About Oort cloud in brief
The Oort cloud is a theoretical cloud of predominantly icy planetesimals proposed to surround the Sun at distances ranging from 2,000 to 200,000 au. It is divided into two regions: a disc-shaped inner OortCloud and a spherical outer Oortcloud. The outer limit of the Oort Cloud defines the cosmographic boundary of the Solar System and the extent of the Sun’s Hill sphere. It may be the source of all long-period and Halley-type comets entering the inner Solar System, and many of the centaurs and Jupiter-family comets as well. The inner Oorts cloud is also known as the Hills cloud, named after Jack G. Hills, who proposed its existence in 1981. The Hills cloud may have trillions of absolute magnitudes with objects larger than 1 km in diameter with neighboring objects tens of millions of kilometres apart. Earlier it was thought to be more massive, but improved knowledge of the distribution of long- period comets led to lower estimates of its mass. If the outer Oorts have been published, the total mass of the inner cloud would be roughly 3×10 kilograms or five times that of Earth. If they have not, the combined mass is roughly 1,000,000 kilograms or 5 times the mass of Earth, and the outer cloud may be 1,500,000 kg or 11 times the size of the Moon. It has been proposed that the cloud formed closer to the Sun and was scattered far into space by the gravitational effects of the giant planets early in the solar System’s evolution.
The cloud is only loosely bound to the solar system, and thus is easily affected by gravitational pull both of passing stars and of the Milky Way itself. These forces occasionally dislodge comets from their orbits within the cloud and send them toward the inner solar System. There are two main classes of comet: short-period comets and long- Period comets. All long- periods comets have very large orbits, on the order of thousands of au, and appear from every direction in the sky. Those relatively rare comets with orbits of about 10,000 au have probably gone through one or more orbits through the Solar system and have had their orbits drawn inward by the gravity of the planets. Some estimates place the outer boundary at between 100,000 and 50,000 au. The region can be subdivided into a sphere-shaped outer Oorting cloud of 20,000–50,000au, and a torus-shaped inward Oort clouds of 2,00,000 – 20,00 au. The outer cloud supplies the long-series comets to inside the orbit of Neptune. It also provides a source of new comets, as the latter’s numbers are gradually depleted as the cloud continues to continue to grow. It was thought it was more massive than previously thought, but better knowledge of its distribution has led to a lower estimate of its size.
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This page is based on the article Oort cloud published in Wikipedia (as of Dec. 06, 2020) and was automatically summarized using artificial intelligence.
