How do comets form??

[Maximus Semprus Veridius]

Hi all!

I have a little bit of homework I need to do, however i'm trying to make a good impression early on in the year to my teacher, (i've alrerady asked him bout angular momentum!). I wondered how comets form, can I have a semi-technical explanation please? I have searched on the web but most places just say " Oooo they come from the Kuiper belt or the Oort cloud" which isn't particularly helpful. Also if you have the time how do asteroids form?? I think this one is a bit more simple though. THANKS!!

[Airbrush]

Comets, and everything else, are debris from massive stars that exploded in supernovae.

[Mr Skeptic]

Comets are thought to have formed outside the solar system (compare with asteroids). What class is this for?

[Ophiolite]

Comets are thought to have formed outside the solar system (compare with asteroids). What class is this for?

Really!!! Care to provide some citations to support that erroneous statement.

 

Comets, traditionally have been seen, like the asteroids, as the rubble left over from the formation of the solar system. The majority were formed within the solar system, beyond the ice line,in the realm of the giant planets. They were ejected from there, into their present orbits by gravitational interaction with the giant planets. There is some recent research suggesting that comets may not be as promordial as previously believed, but they are very much a part of, and formed in, the solar system.

 

This is comet astronomy 101, but if you require references I shall be happy to provide them.

[Airbrush]

Comets, traditionally have been seen, like the asteroids, as the rubble left over from the formation of the solar system. The majority were formed within the solar system, beyond the ice line,in the realm of the giant planets. They were ejected from there, into their present orbits by gravitational interaction with the giant planets.

 

The question is HOW do comets form? You are only telling us WHERE they form.

 

They are the result of supernovas. Now I would like to know how do these things form as solid objects after a supernova? My best guess is when a star explodes it throws out chunks of matter in many sizes, more small pieces than big pieces.

Edited September 21, 2010 by Airbrush

[Ophiolite]

The question is HOW do comets form? You are only telling us WHERE they form.

 

They are the result of supernovas. Now I would like to know how do these things form as solid objects after a supernova? My best guess is when a star explodes it throws out chunks of matter in many sizes, more small pieces than big pieces.

The supernova creates, or contributes to a GMC, a giant molecular cloud. At some point gravitational instability causes a portion of this cloud to collapse.

The central portion becomes the proto-sun, while the remainder of the collapsing part forms a disc around the star.

Particles begin to condense out of the cloud and over time these particles coalesce through collisions and gravitational attraction into sizeable bodies called planetesimals.

Some of these planetesimals are rocky, some are icy. Some become large enough that they partially melt and differentiate.

Many collide to form large bodies that go on to become planets and the major moons.

Other are ejected from the system entirely by the gravitational influence of the giant planets, which form rapidly and early in the system.

In the region of the giant planets, where temperatures are lower, many of the bodies are icy. These are the proto-comets.

Under the influence of the giant planets these are ejected to form the Oort cloud and the Kuiper belt.

 

The above is greatly simplified, but captures the main features of the process.

[Mr Skeptic]

Really!!! Care to provide some citations to support that erroneous statement.

 

Comets, traditionally have been seen, like the asteroids, as the rubble left over from the formation of the solar system. The majority were formed within the solar system, beyond the ice line,in the realm of the giant planets. They were ejected from there, into their present orbits by gravitational interaction with the giant planets. There is some recent research suggesting that comets may not be as promordial as previously believed, but they are very much a part of, and formed in, the solar system.

 

This is comet astronomy 101, but if you require references I shall be happy to provide them.

 

I mean farther away than any of the planets. Eg the Kupier belt for the short-period comets or the Oort cloud for the long-period ones.

http://www.nasa.gov/worldbook/comet_worldbook.html

 

Whereas asteroids are mostly in the asteroid belt (between Mars and Jupiter). But yes, there is some overlap between the two; after all they are rather arbitrary classifications.

http://www.nasa.gov/worldbook/asteroid_worldbook.html

[Ophiolite]

I mean farther away than any of the planets. Eg the Kupier belt for the short-period comets or the Oort cloud for the long-period ones.

This is where they currently reside, but it is not where current theory envisages they were formed, as I noted in my preceding post. Your statement remains incorrect and potentially confusing for Maximus.

[Maximus Semprus Veridius]

Thanks everyone who gave information towards my question! I think my Geology teacher will be most impressed, (btw that was the answer to your question the lesson is Geology at AS level, however our group seems to grasp things quick so he goes on to some better and more interesting stuff!).

 

CHEERS!

[Airbrush]

The supernova creates, or contributes to a GMC, a giant molecular cloud. At some point gravitational instability causes a portion of this cloud to collapse.

The central portion becomes the proto-sun, while the remainder of the collapsing part forms a disc around the star.

Particles begin to condense out of the cloud and over time these particles coalesce through collisions and gravitational attraction into sizeable bodies called planetesimals.

Some of these planetesimals are rocky, some are icy. Some become large enough that they partially melt and differentiate.

Many collide to form large bodies that go on to become planets and the major moons.

Other are ejected from the system entirely by the gravitational influence of the giant planets, which form rapidly and early in the system.

In the region of the giant planets, where temperatures are lower, many of the bodies are icy. These are the proto-comets.

Under the influence of the giant planets these are ejected to form the Oort cloud and the Kuiper belt.

 

The above is greatly simplified, but captures the main features of the process.

 

Nice explanation Ophiolite. How about this GMC (giant molecular cloud)? Are you saying that a supernova totally pulverizes the star into molecular-sized particles only? No big pieces?

 

I had visualized it the following way. When the star supernovas it scatters plasma in all directions. These plasma "droplets" range in size from molecular to rather large clumps of plasma miles across. As this plasma cools it becomes liquid globs and later solid clumps of matter in a wide range of sizes, from tiny up to the size of comets and asteroids many miles in diameter. These comets and asteroids later clump together to form planets and most crash into the new central star. So this would make comets and asteroids the largest and most ancient original building blocks in solar system formation. Comets and asteroids are solidified supernova "droplets".

Edited September 23, 2010 by Airbrush

[DanielC]

Nice explanation Ophiolite. How about this GMC (giant molecular cloud)? Are you saying that a supernova totally pulverizes the star into molecular-sized particles only? No big pieces?

 

I had visualized it the following way. When the star supernovas it scatters plasma in all directions. These plasma "droplets" range in size from molecular to rather large clumps of plasma miles across. As this plasma cools it becomes liquid globs and later solid clumps of matter in a wide range of sizes, from tiny up to the size of comets and asteroids many miles in diameter. These comets and asteroids later clump together to form planets and most crash into the new central star. So this would make comets and asteroids the largest and most ancient original building blocks in solar system formation. Comets and asteroids are solidified supernova "droplets".

 

Just think about it for a minute. Why would you get big pieces? Before the supernova you have a star that is basically made of gas with a core of degenerate matter surrounded by a shell of plasma. Nothing here is solid in the sense that you and I understand the term "solid". When fusion stops at the core, you have a collapse. This collapse is driven by gravitational potential energy and it is so energetic that it actually runs fusion backward (photons have enough energy to break atomic nuclei into lighter elements). This energy tears apart the outer ~85% of the star leaving behind only a small ~15% which is the core of degenerate matter that we call a neutron star. Looking at this process, why should you expect there to be any kind of big solid pieces of any kind? At these energies you shouldn't even expect molecules. The energy that the particles have is many orders of magnitude greater than inter molecular forces. There should be no molecules at all, much less "big pieces".