The big question I'm going to address in this segment is how did the solar system
form, and how did we work that out.
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The idea of how we actually form
planetary systems has a long legacy.
It goes back to the concepts of Immanuel Kant and
Pierre-Simon Laplace back in the 1700s.
So in Laplace's model for the formation of the solar system,
essentially we start from a molecular cloud of gas and dust.
It slowly condenses in under it's own self gravity.
Forms a central bulge which eventually becomes the protostar.
But as the cloud actually condenses in the small rotation
the cloud has becomes accelerated.
Becomes faster and faster and forms a central disc around that star region, and
that disc is the material which eventually condenses out to form the planetary system
we see today.
So this is a picture of typical stellar nursery, this is probably a similar
environment to where the sun and our planetary system first formed.
And in the visible,
the things the arrows are pointing to you barely see anything at all.
These things are very, very faint invisible light, yet
in the infrared, they're glowing like a Christmas tree.
They're extraordinarily bright.
These aren't typical stars.
These aren't emitting a lot of light in the visible.
They're emitting most of their energy down in the infrared as heat.
This is typical of a dust disc around a newly forming star.
It's obscuring a lot of the visible light, but it's quite hot so
it's emitting a lot of energy down in the infrared.
So what this Spitzer space telescope enabled us to see is the dust discs
around newly forming planetary systems in a stellar nursery.
We actually see these dust rings around other planetary bodies today.
This particular dust ring is the Formalhaut dust ring.
So, you can see the central glowing star and, also,
a much more diffuse ring of dust around that glowing star.
And, we think that's caused by the collisions of comets in the outer parts of
the stellar system.
This is another example of a dust ring.
This is HR 8799 in Pegasus, and
this is an infrared dust cloud all the way out to the stellar system's Kuiper belt,
so for us that would be out past the orbit of Pluto.
And this system has up to about three planets
inside that dust cloud which are disturbing local comets and
causing them to collide and generating this dust that we see in the infrared.
When Laplace first developed his theory for solar system formation,
he used the tools available at the time, which, being one of the greatest
mathematicians of his age, was a mathematical analysis of the problem.
These days, we can move beyond the simple pen and
paper mathematics approach to actually simulating these processes in a computer.
So we're building the physics, as we understand it,
of these clouds into the models, and then we simulate them.
We let them run forward in time and see what happens.
And the structures we form from these models look remarkably like the structures
we see.
But there's still a few big unknowns.
What actually caused the condensation of this molecular cloud to start with?
Well probably somewhere in a stellar nursery was the reason
that the sun formed when it did 4.5 billion years ago.
The other big unknowns, how do you get from a diffused cloud of gas and dust,
how do you bring that material together to start forming
solid grains which then build up to form the planets?
Or do you even need to?
Do the planets form from initially solid grains accreting together into
small rocks and
asteroid-like bodies called planetesimals which then go on to form larger planets?
Could you actually just take the gas from a disc and form a planet from it directly?
These are still the big unknowns in modern Laplacian theory for
the formation of the solar system.