Oort Cloud Our Glaxy Surrounds

The Oort cloud is thought to occupy a vast space from somewhere between 2,000 and 5,000 au (0. 03 and 0. 08 ly) to as far as 50,000 au (0. 79 ly) from the Sun. Some estimates place the outer edge at between 100,000 and 200,000 au (1. 58 and 3. 16 ly). The region can be subdivided into a spherical outer Oort cloud of 20,000–50,000 au (0. 32–0. 79 ly), and a torus-shaped inner Oort cloud of 2,000–20,000 au (0. 0–0. 3 ly). The outer cloud is only weakly bound to the Sun and supplies the long-period (and possibly Halley-type) comets to inside the orbit of Neptune. The inner Oort cloud is also known as the Hills cloud, named after Jack G. Hills, who proposed its existence in 1981. Models predict that the inner cloud should have tens or hundreds of times as many cometary nuclei as the outer halo; it is seen as a possible source of new comets to resupply the tenuous outer cloud as the latter’s numbers are gradually depleted. The Hills cloud explains the continued existence of the Oort cloud after billions of years.



The screaming winds could be carrying the dust raised from the dunes across great distances, contributing to the global cycle of organic dust on Titan. These would result in effects similar to those that occur on both Earth and Mars. Water in its life-sustaining liquid phase exists beyond our own planet, both in our Solar System--and elsewhere. With oceans of water sloshing around on 71% of our own planet's surface, Earth still remains the only planet known to have stable bodies of liquid water. Liquid water is essential for all known life forms on Earth. The existence of water on the surface of Earth is the outcome of its atmospheric pressure and a stable orbit in our Sun;s circumstellar habitable zone. The habitable zone is that Goldilocks region, surrounding a star, where the temperature is not too hot, not too cold, but just right for life sustaining water to exist in its liquid phase. However, the origin of Earth's water still remains unknown. A billion years ago, our Moon was closer to Earth than it is now. As a result, it appeared to be a much larger object in the sky. During that ancient era, if human beings had been around to witness such a sight, it would have been possible to see the entire Moon--not merely the one near side face that we see now. A billion years ago, it took our Moon only twenty days to orbit our planet, and Earth's own day was considerably shorter--only eighteen hours long. Stupendous, almost unimaginably enormous tides, that were more than a kilometer in height, would ebb and flow every few hours. However, things changed, as the lunar orbit around our primordial planet grew ever wider and wider. Annually, Earth's Moon moves about 1.6 inches farther out into space. Currently, the lunar rate of rotation, as well as the time it takes to circle our planet, are the same.