Oort Cloud - Agreed Terms.


The devil is in the detail
THREAD Re-STARTED HERE and consolidated.

Oxford Dictionary of Astronomy
Ian Ridpath Oxford University Press 2011

"A roughly spherical halo of comet nuclei surrounding the Sun, out to perhaps 100,000 AU (over one third of the distance to the nearest star). Its existence was proposed in 1950 by J H Oort to account for the fact that new comets approach the Sun on highly elliptical orbits at all inclinations."
"The Oort Cloud remains a theoretical concept, since we cannot currently detect comets at such great distances. The cloud is estimated to contain 10^12 comets remaining from the formation of the Solar System. The most distant members are fairly loosely bound by the Sun's gravity. There may be a greater concentration of comets relatively close to the ecliptic, at 10,000 to 20,000 AU from the Sun, extending inwards to join the Kuiper Belt. Oort Cloud comets are affected by the gravitational influence of passing stars, occasionally being perturbed into orbits which take them through the inner Solar System."

The Oort cloud is sometimes called the Öpik–Oort Cloud

View: https://imgur.com/a/1DJboMw

Don't forget comets do not develop a tail until near the Sun, so are otherwise not easily visible, especially at great distances. Comet Tempel 1 NASA.

Asteroids, Meteorites and Comets Linda T Elkins-Tanton Chelsea House 2006

"Long period comets have traditionally been thought to come from a gigantic, diffuse cloud, about 30,000 to 100,000 AU from the Earth. This region is called the Oort Cloud, after the astronomer Jan Oort, who first demonstrated its existence. It is thought that most of these comets originated near Uranus and Neptune. Oort suggested that there are about 100 billion comets in the Oort Cloud. Comets are thought to be perturbed out of the Oort Cloud by a number of processes, including passing stars. It is thought that the heavy, early cratering on Jupiter's and Saturn's satellites was caused by Oort Cloud bodies. Some scientists also think that the Earth's water budget came from these bodies."

Complete History of the Universe All About Space 2016

"Oort Cloud
An enormous region of space encapsulating the planets and stretching 50,000 AU from the Sun to around 100,000 AU in diameter at its outer boundaries: from one side to the other its about 2 light years long."
"It's made of water, ammonia and methane ice, in the form of icy particles and trillions of larger bodies. It's suspected that many of the Solar System's comets were born here, and some trans-Neptunian objects are Oort Cloud members too. It's divided into two distinct regions, the inner and outer Oort Cloud containing several trillion comets larger than 1 km (0.62 mile) in diameter. [These must be estimates, since they cannot be seen at this distance] Considering the size of the Oort Cloud, it would take our fastest spacecraft launch, New Horizons, around 20,000 years to reach its outer edge at 58,536 km/hour (36.373 miles/hour. The Oort Cloud isn't very massive, just a fraction pf the 100 or so Earth masses of material ejected from the centre of the Solar System."

Collins Discovery Guide - Universe Pam Spence William Collins 2018

"The most spectacular objects in the Solar System are the comets, which can produce awe inspiring tails millions of km long. Cometary orbits are not confined to the plane of the Solar System, where the planets and asteroids are found, but can approach the Sun from any angle. This fact, together with the numbers of new comets observed each year, suggests that there is a reservoir of cometary material surrounding the Solar System. This reservoir is called the Oort Cloud which is believed to extend from around 30,000 to 100,000 AU."
"The Oort Cloud has never actually been observed - its existence was suggested by the Dutch astronomer J H Oort to explain the trajectories and number of long period comets (comets that take 200 years or more to orbit the Sun) that are seen. However, comets have been seen coming directly from that far out and it is the logical explanation for their origin.

What is the Oort Cloud?
For thousands of years, astronomers have watched comets travel close to Earth and light up the night sky. In time, these observations led to a number of paradoxes. For instance, where were these comets all coming from? And if their surface material vaporizes as they approach the sun (thus...

View: https://imgur.com/a/neeV7vm

"The Oort Cloud is a theoretical spherical cloud of predominantly icy planetesimals that is believed to surround the sun at a distance of up to around 100,000 AU (2 ly). This places it in interstellar space, beyond the sun's Heliosphere where it defines the cosmological boundary between the solar system and the region of the sun's gravitational dominance."

So one suggestion is that the Oort Cloud is a hypothetical subdivision of interstellar space; nonetheless, inhabited by large numbers of comets - which can be diverted towards the inner Solar System - and possibly other objects.
The dust and (frozen) water are natural inhabitants of such an environment.

WORK IN PROGRESS last edit 18th August 17.20 BST.
  • Like
Reactions: sam85geo
Dec 9, 2020
I still vividly recall inadvertently watching a comet many years ago. I looked up and there it was; It seemed a cold, riveting, sobering sight in the chill night sky. It was an event that fostered my interest in Astronomy and Cosmology. I think it was comet Shoemaker-Levy before its spectacular demise.
  • Like
Reactions: Catastrophe
Feb 14, 2020
Can a comet's orbit around the Sun not identify its farthest point in elliptical orbit?
If it is in Kuiper belt at so many AUs then it belongs to Kuiper Belt, if it is farther than it is most likely from Oort Clouds.
The latter are likely to be rare as these are captured by perturbations to gravity field from other cosmological events such as other stars or movement of milky way stars affecting Sun's gravity field, most likely from near Sun Stars!

Can other astronomical observations, visible or other spectral lines shed more light and has examination of that space been captured in Hubble, Chandra or other observatories in Space?


The devil is in the detail
Reasonable question, but with the Oort Cloud being so loosely defined, would anything be lost by just saying > 30 AU? Where would you make a division? 100 AU? 200 AU? Is it any more meaningful than perihelion? I am no expert. Are there comets with high aphelion and low perihelion, compared with medium aphelion and medium perihelion? (Whatever they might mean).

Cat :)
  • Like
Reactions: sam85geo



Latest posts