The Oort Cloud is an immense spherical cloud surrounding the planetary system and extending approximately 3 light years, about 30 trillion kilometers from the Sun. This vast distance is considered the edge of the Sun's orbit of physical, gravitational, or dynamical influence.
In 1950, a Dutch astronomer Jan Oort proposed that certain comets come from a vast, extremely distant, spherical shell of icy bodies surrounding the solar system. The giant swarm of objects is named the Oort Cloud, occupying space at a distance between 5,000 and 100,000 astronomical units. (One astronomical unit, or AU, is the mean distance of earth from the Sun : about 149.6 million kms.) The outer extent of the Oort Cloud is considered to be the "edge" of our Solar system, where the Sun's physical and gravitaional influence ends.
WHAT DOES IT CONTAIN?
The Oort Cloud probably contains 0.1 to 2 trillion icy bodies in solar orbit. The objects in the Oort Cloud and in the Kuiper Belt(a region of the solar system beyond the orbit of Neptune) are presumed to be remnants from the formation of the solar system about 4.6 billion years ago. The Kuiper Belt extends from about 30 to 55 AU and is probably populated with hundreds of thousands of icy bodies larger than 100 kilometres across and an estimated trillion or more comets.
Based on the analysis of past comets, the vast majority of Oort Cloud objects are composed of icy volatiles – such as water, methane, ethane, carbon monoxide, hydrogen cyanide, and ammonia.
COMETS
Recognition of the Oort Cloud gave explanation to the age old questions : "What are Comets, and where do they come from?" The existence of the Oort Cloud is the physical evidence of long-period comets entering the planetary system. When Jan Oort determined the rotation of the Milky Way galaxy in the 1920's, he interpreted comet orbital distribution with only 19 well-measured orbits to study and successfully recognized where these comets came from.
Short-period comets have orbits that last up to two hundred years while the orbits of long-period comets can last for thousands of years. Whereas short-period comets are believed to have emerged from either the Kuiper Belt or the scattered disc, the accepted hypothesis is that long-period comets originate in the Oort.
Two recent Oort cloud comets were Hyakutake and Hale-Bopp. Hyakutake was average in size, but came to 0.10 AU (15,000,000 km) from Earth, which made it appear spectacular in the night sky. Hale-Bopp, on the other hand, was an unusually large and dynamic comet, ten times that of Halley at comparable distances from the sun, making it appear quite bright, even though it did not approach closer than 1.32 AU (197,000,000 km) to the Earth.
EXPLORATION
Due to its vastness, the region has remained unexplored and largely undocumented. Voyager 1, the fastest and Carthest of the interplanetary space probes currently exiting the Solar System will reach the Oort Cloud in about 300 years, and will will take about 30,000 years to pass through it.
DRAWBACKS
- Due to insufficient power to operate the probe’s radioisotope thermoelectric generators, it will be non functional by around 2025, when it will reach the Oort Cloud.
- The Oort Cloud is incredibly distant from Earth. By the time a robotic probe could actually reach it and begin exploring the area in earnest, centuries will have passed here on Earth.
