Planetary formation 101: how is it that?

[yusufcam (Colin)]

okay my simple understanding .....

our solar system.....

sun is formed

to the greater extent the rest of the debri of the cloud from which it was born organizes itself through gravitational attraction slowly into the planets of our solar system. (yes/no?)

why then are the planets so different from each other if this is how they are formed?

curious?

[yusufcam (Colin)]

wiki has an interesting section on this topic....

http://en.wikipedia.org/wiki/Nebular_hypothesis

didn't realize it was so speculative till i read that, when i've seen variants of the idea before it was always presented like fact.

hmmm....

how the nebular hypothesis coalesced into a fact?

[CraigS]

Hi Colin;

Great question !!

I too, am in awe of the thing which sits right in our faces when we start looking even in our own back-yards !

Its sitting so close to our own faces, that we mostly forget about it ..

and that thing is … Diversity !!

The variances within our own Solar System, even within our own so-called 'Habitable Zone', are absolutely mind-boggling !

Diversity from similar beginnings is another hallmark of Chaotic systems. Prediction of the outcomes within such systems is not possible.

Check out this classical physics oriented article.
Our unlikely solar system

Recent modeling of solar mass stars with planetary systems, found that a system with four rocky planets and four gas giants in stable orbits – and only a sparsely populated outer belt of planetesimals – has only a 15 to 25% likelihood of developing. While you might be skeptical about the validity of a model that puts our best known planetary system in the unlikely basket, there may be some truth in this finding.

And I'll say that this is just the tip of the iceberg, in terms of us recognising what's been ignored for so long. Trying to crudely model how a system forms, using classical physics at macros scales, ignores the most obvious observational evidence at hand - Diversity of environments.

Whilst the Laws of Physics are real, and for the most part, all known matter follows these 'rules', chaotic results can still ensue. And all of this still fits within the realms of mainstream science !

Cheers

[yusufcam (Colin)]

Originally Posted by CraigS

Hi Colin;

Great question !!

Check out this classical physics oriented article.
Our unlikely solar system

Cheers

yes, good article....

makes our solar system seem quite unusual (lucky for us)...

i'll have a look at the chaos thread....

thanks

[renormalised (Carl)]

Planetary system formation is a very complex beast and whilst we may know the basics to a certain degree, the nitty gritty is still a long way from resolution. There is still a lot to learn, even when including all the planetary systems we've found over the last 15-20 years. Quite frankly, we still don't know enough to really say what's your average planetary system and how they form, simply because we just don't have enough examples to confidently say anything about them. It's most a matter of "best guesstimates" so far as the theory goes. However, we can rule out some processes simply because of their physical improbability. In other words, given what we do know, the Nebula (Accretion Disk) Theory is the best we have to explain how the process happens...plus it fits the data we do have.

[mswhin63 (Malcolm)]

just out of curiosity with regards to Jupiter does anybody think it is possible that this was the first planet to form because of its cause intense hydrogen. Is quite possible that when our solar system was part of a gas cloud that Jupiter sucked up most of the hydrogen gas leaving the other planets to collect the remainder. Possibly Saturn, Neptune and Uranus may have taken up all the other gaseous elements leaving only the heavier elements to form the rocky planets.

It is quite common to find Exoplanets that gas planets are located very close to the located star. So recent science suggests that larger gas planets can pretty will form anywhere. Or maybe they are attracted by though stars gravitational attraction. It is a difficult to observe especially seeing the science is so recent.

I must admit this is an area that we have not been dealing with much in my uni studies so I am also interested to to understand how this works for future reference.

[CraigS]

Hmm interesting.

What if:

What we're chasing, in the form of more knowledge derived from detailed present-day observed conditions, results in models from which no predictability emerges?

Cheers

[DJDD]

I cannot remember the details but there is an article in this months AS&T (or last month's) about this very topic.

not helpful but...

[renormalised (Carl)]

Originally Posted by CraigS

Hmm interesting.

What if:

What we're chasing, in the form of more knowledge derived from detailed present-day observed conditions, results in models from which no predictability emerges?

Cheers

Too bad, but we have to be very careful about what we might believe about the nature of indeterminate systems such as these. They may not be as unpredictable as they seem. What we may see as being unpredictable might in fact be ordered. Our scope of inquiry is by its nature limited, so we cannot know for certain whether a system has any true unpredictability or order to it. If it appears that 15-20% of systems eventually end up with terrestrial planets, for argument's sake, then there must be some underlying order present despite the seeming unpredictability to the processes involved.

[CraigS]

Originally Posted by renormalised

Too bad, but we have to be very careful about what we might believe about the nature of indeterminate systems such as these. They may not be as unpredictable as they seem. What we may see as being unpredictable might in fact be ordered. Our scope of inquiry is by its nature limited, so we cannot know for certain whether a system has any true unpredictability or order to it. If it appears that 15-20% of systems eventually end up with terrestrial planets, for argument's sake, then there must be some underlying order present despite the seeming unpredictability to the processes involved.

Ah .. the ol' 15-20% of systems eventually ending up with terrestrial planets prediction, eh ?
(I'm still stuck in 'Get Smart' mode, from yesterday .. just kidding …)

Even a probable outcome is not a dead certainty.

There's still plenty of space for unpredictability in there.

And yep .. sure …. there's plenty of order, (and deterministic sub-systems), in amongst all of the elements in the mix (gee .. we see it here on Earth, everyday).

Both order and chaos are assured outcomes. But how does this impact the statistic quoted ?

(Happy to read up more on the model .. I have no idea about whether or not they included any non-deterministic logic ..I'll bet they haven't .. but will have a read when I get the chance. )

Cheers

[Astro78]

Great topic. We're also seeing what's called an "Infrared excess" around young stars in Orion which puts the core accretion model into the forefront. The dust is cooler than the star and emits more light at longer wavelengths than the star would alone. At about 5 million years old the stars no exhibit this "infrared excess".

Disk instability is my favourite model (although don't believe it). It goes something along the lines of massive gravitational collapse of a gas cloud and forms planets in <1000 years.

[mswhin63 (Malcolm)]

I thought of something that may also be a factor and and why there are so many Binary or Trinary stars out there.

Most of the Exoplanets that have been discovered a very large Jupiter sized or larger and are also orbiting very close to their companion star.
A Brown dwarf is the star that didn't ignite and they are also around about the size of Jupiter or maybe a bit more. It may be possible that these gas giants found around the stars are the start of a possible binary star that just didn't have enough gravitational forces to ignite the centre of the planet's into nuclear fusion. As you can imagine Jupiter is an extremely hot planet with its own power source. So it is quite possible that when a a star explodes and leaves loads of hydrogen gas behind that the first thing that is accumulated is hydrogen gas to form a large gas giants. some of these gas giants may be big enough to start nuclear fusion and thus creates a binary star, others to simply failed to start.

Just an idea but would need a lot of data to be collected to at least start confirmation.