h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Does the oort cloud realy exist, how big are it's component pieces, how many are there and how big is the cloud???

Taff
Agent of kaos

It probably exists. We've never observed it directly, but long period comets have to come from somewhere.

Its component pieces are probably quite small individually (up to say a couple of km across).

There are likely to be numbers in the trillions, with a total mass several, although not hundreds of, times that of the Earth.

The cloud is BIG.

Earth is 1 AU from the Sun. Pluto is about 50 AU.

The Oort cloud *starts* somewhere outside the orbit of Pluto and goes out in all directions to over 1.5 light years. Imagine a sphere with a diameter of three light years - BIG. The orbit of the earth is a sphere in the centre eight light MINUTES across.

So the Oort cloud, if it's there, is huge. But as Slartibartfast said, the interesting thing about it is how dull it is. There's so much of it, and so little in it.

Warning - Pedant moment - warning.

The Earth's orbit is 16 light minutes across (diameter) and has an 8 light minute radius (1 Astronomical unit).

SoRB

turvy

1.5 light years, thats abouy half way to the next nearest star,

if the gravity of stars is big enough to affect small objects at that distance shouldn't we see clumps of matter at the lagrange point between the two stars, if the oort cloud exists,

or perhaps long period commets are just hunks of junk wizzing through interstella space???

"shouldn't we see clumps of matter at the lagrange point between the two stars"

Well, yes... if there was such a thing. But for a Lagrange point to be anything close to stable, it has to consist of two bodies that are close to each other, relative to any other similar sized bodies. An example would be the earth and moon - the distance between them is *tiny* compared to the distance to the next reasonable sized body, Venus.

But while the Sun is only 4.2 ly from Proxima Centauri, it's also not that far from a whole bunch of other stars. I can think of no better way to envisage it than to go and buy one of these beautiful objects: http://www.bathsheba.com/crystal/starmap/ . You can see how many stars there are within 5 parsecs - quite a few. A stable Lagrange point anywhere in that 3D mess of objects is unlikely.