Oort Cloud?
The Oort cloud is a theoretical concept of a huge spherical shell of icy objects that surrounds the Sun and the rest of the solar system. It is named after the Dutch astronomer Jan Oort, who first proposed its existence in 1950. The Oort cloud is thought to be the source of most long-period comets, which have orbits lasting thousands or even millions of years.
The Oort cloud is very far from the Sun, much farther than the planets and the Kuiper belt. The inner edge of the Oort cloud is estimated to be between 2,000 and 5,000 astronomical units (AU) from the Sun, while the outer edge could be as far as 100,000 AU or more. One AU is the average distance between Earth and the Sun, about 150 million kilometers (93 million miles). To put this in perspective, Pluto's orbit ranges from about 30 to 50 AU, and the nearest star to the Sun, Proxima Centauri, is about 268,000 AU away.
The Oort cloud contains billions or trillions of icy objects, ranging in size from mountains to larger than Pluto. These objects are remnants of the early solar system, when planetesimals (small rocky and icy bodies) formed and some were scattered far away by the gravitational influence of the giant planets. The Oort cloud is not a solid structure, but a diffuse and dynamic population of objects that are loosely bound to the Sun. They can be perturbed by the gravity of passing stars, galactic tides, or even dark matter, and some of them can fall into the inner solar system as comets.
Because of its immense distance and faintness, the Oort cloud has never been directly observed by any spacecraft or telescope. Its existence and properties are inferred from the observation and analysis of long-period comets and other indirect evidence. Scientists hope to learn more about the Oort cloud and its origin by studying these comets and by future missions to the outer solar system.
References:
- Oort cloud - Wikipedia
- Overview | Oort Cloud – NASA Solar System Exploration
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