Most of us think that the Solar system ends at Pluto. In fact most astronomers thought that this was the case. But then somebody asked the question: where from do the comets come from??? We will try to answer this question in this VERITAS and we will learn about worlds beyond Pluto.
In 1950 a Dutch astronomer Jan Oort suggested that comets come from a vast reservoir of icy bodies at the distance of 50,000 AU( AU means Astronomical Unit. 1 AU is the distance from Earth to the Sun). About a year later Gerard Kuiper suggested that 50,000 AU is too far away for comets and that comets are placed just beyond the orbit of Neptune ( Neptune is placed at about 30 AU).
Today we know that both these theories are true. There is a belt of icy bodies just beyond the orbit of Neptune. We call it the Kuiper belt. We know of atleast 70,000 objects in this belt each with a diameter of atleast 100 kilometres. Astronomers are sure that there are more.
And there are zillions of more objects with diametres between 10 and 50 Kms in this belt. The Kuiper belt extends from 30 to 50 AU. Many astronomers are of the opinion that Pluto should not be called a planet but a Kuiper Belt Object(KBO). This is because of its small size and its funny rotation ( it does not rotate on a North-South axis but on a East-west axis i.e it rotates on its side).
Most of the short period comets come from the Kuiper belt.
Helley’s comet is a short period comet( just 76 years) and it comes from the Kuiper belt.
The long period comets come from the OOrt Cloud. There are comets humans have seen just once. These comets might have the priod of thousands of years. When Jan OOrt observed these long period comets he realized that thay come from somewhere very far away. He also noticed another strange things: these comets come from any direction in space. These facts made him hyphothesize that these comets come from a spherical cloud about 50,000 Au from us. Note that all the planets and the Kuiper belt lie on one plane and this is the plane in which the equator of the Sun is at the centre. This is because the Sun’s gravity is strongest here. But at the distance of 50,000 AU the sun is just a small spec of light and thus the oort cloud is not located in a plane. It is spherical.
So we are surrounded by a spherical cloud of small icy worlds.
They are held in that spherical cloud by the gravity of Sun.
See how far Sun’s Gravity can be felt. The diameter of the Oort cloud is about 2 light years!!!! The sun’s gravity has trapped things even to a distance of 1 light year!!!!!!!!
But wait a minute! How far is the nearest star? It is just 4 light years away. This OOrt cloud is affected by that star too. So every once in a while this star(Alpha centauri) perturbs an object of the OOrt cloud. Remember that the OOrt Cloud objects are very loosely bound to Sun’s gravity. So a small push by a passing star is enough to move them. When perturbed this object falls “down”.But where? It falls towards the sun. It is this object that comes hurling towards the sun that we call a comet. What a traveller. What a sight from Earth.
Short period comets are formed when a Kuiper Belt object is perturbed by one of the outer large planets.
OOrt cloud and Kuiper belt are remains of the formation of the solar system. The giant planets Jupiter, Saturn, uranus and Neptune created a lot of left overs when they were being formed. Some of this debry was set into orbit and formed the Kuiper Belt. The rest of the debry way kicked out of the solar system. It however could not escape the gravity of sun altogether and went to form the OOrt Cloud.
See the attached illustration of the Kuiper belt and the OOrt cloud. See how little the Sun is. And what a small portion of this entire thing is the solar system till pluto. Also see the spherical OOrt cloud surrounding the sun and planets.
Friends, The earth is a small place in this grand scheme of things. It is no doubt our home but lets not restrict our thinking to just our little home. Lets explore beyond the farthest reaches of space and time. The human brain constantlyt searches for infinity.
Lets not deny it its pleasure:
THE BRAIN is wider than the sky,
For, put them side by side,
The one the other will include
With ease, and you beside.
The brain is deeper than the sea,
For, hold them, blue to blue,
The one the other will absorb,
As sponges, buckets do.
The brain is just the weight of God,
For, lift them, pound for pound,
And they will differ, if they do,
As syllable from sound.
( – Emily Dickenson)
Go, wondrous creature! mount where Science guides:
Go, measure earth, weigh air, and state the tides:
Instruct the planets in what orbs to run,
Correct old time and regulate the Sun;