View Full Version : How are gas giants formed?

Algenon the mouse
2004-Nov-25, 08:10 PM
I recently read an article in "National Geographic" about gas giants. In the article it stated that there are two current theories about the formation of gas giants. Since there is a lot of people online who know more about gas giants than I do, I thought I would ask who believes which theory and why.

Theory one(core Accretion) states that the formation of most gas giants is a slow process in which tiny dust grains stick together forming larger gains until the growth process eventually yeilds solid cores roughly ten times the size of earth. Then the powerful gravity sucks in gas to create a gas giant. This could take several millions of years. Those oppose to this theory say that the process is too slow and the gas would not linger for that long.

Theory two states gravity causes the disk of gas and dust to collaspe into dense clouds. the cloud shrinks and solid material falls to the center creating a core. When the rest of the gas contracts, it forms a gas giant. Those oppose to this theory state that gas giants are far too common for this theory to work.

2004-Nov-25, 08:38 PM
We don't "know" how gas giants form, but it is a good bet that there is some variation from gas giant to gas giant. The scenario I imagine to be the case is this: Some begin as your type two, but the process stops at some point when gas gets blown out of the proto-solar system from a nearby supernova, or onset of fusion in the most massive core in the system. Then a dusty disk forms around the new star and accretion of the dust commences.

If this is how it works, I would guess that most of Jupiter's mass is from your type 2, and some from type 1. Saturn is closer to an even proportion, and the other planets are mostly type 1 accretion.

2004-Nov-25, 09:18 PM
Anton's right.

However, from what I've read on websites previously, gas giants were formed in just a few hundred years, not several million as was previously thought - an astrophysicist called Thomas Quinn, from the University of Washington, claimed that the disk of matter which spins round a young star begins to break up and congeal into planets more quickly than earlier thought - he's one of the scientists who researched into a mathematical model which proves to show exactly how and how long it took the planets to form.

It's assumed that the gravity of the resulting clusters of matter when gas giants are formed basically pulls in the surrounding gas that makes up the vapour "shrouds" around giant gas planets.

Of course this is meerly one piece of research and back to what I firstly said, that Anton's right - we don't actually know!

Hope this helps

2004-Nov-27, 01:35 AM
But a gas giant will start out as a huge spread of particles orbiting the star in a similar pattern. The primary component would be gas as the lightest particles not in the sun would have been flung further away. How a gas giant goes from this stage to the finished product Anton and Rigel have answered.

2004-Nov-27, 06:13 PM
I think a general opinion is emerging in astronomy that gas giants can form by either core accretion or cloud collapse; it may be the case that neither is mutually exclusive. Given that some exoplanetologists think that there may be two types of planetary systems--eccentric ones and regular ones, like our own--I wouldn't be surprised if the process of planetary formation is much less easily categorizable than we want to think.