Beginning of the Solar System

Wayne Lee
Mission Designer
Jet Propulsion Laboratory, NASA/Caltech

The most noticeable force that shapes our solar system, of course, is gravity, uh... Gravity is what keeps all the planets in orbit around the Sun. It's what keeps us, uh, glued down to the surface of the Earth. It keeps us from floating away as we're trying to walk to school every day. It keeps your peas on your dinner plate so you can eat them. It turns out that if the Sun did not pull on the planets with its gravitational force, they would just fly off into the Universe never to be seen from again.

I'd say the second fundamental force that shapes the solar system is probably what we call the "nuclear force." And the nuclear force is what allows fusion to occur inside, deep inside the Sun. And, of course, nuclear fusion is the process that produces ...the heat and light that comes out of the sun and warms all the planets.

As far as we know, our universe originated from "nothing."

Then in an instant... and time began.

We call this..."the big bang"... and date it at about 15 billion years ago.

From a point smaller than an atom, everything leapt into being, first as pure energy...

Then, after several hundred thousand years, matter condensed and structure began to develop.

Galaxies and stars emerged from primordial chaos.

Stars are born when gravity draws in gas and dust.

In their cores, hydrogen-the simplest element in the universe-fuses together in thermo-nuclear reactions to form helium, releasing energy.

Some stars are so large that after a lifetime of building up heavier elements like iron, they die in colossal supernova explosions.

Supernovas enrich the clouds of interstellar gas and, perhaps, trigger the next generation of star formation.

This is how we think our solar system began.

First, our star, the Sun, turns on, some 4 to 5 billion years ago.

Instabilities farther out in the disk cause regions of matter to condense and grow.

Too small to become stars, these will be planets.

Close to the Sun, they're made of rock, iron and other solid matter.

The young Sun blows away much of the original gas, leaving at most a thin atmosphere.

Farther out, what will become the giant planets retain much of the gas that gave them birth.

This young solar system was a place of tremendous violence.

Objects too small to be planets smash into larger ones, leaving the vast numbers of craters still to be seen on the Moon and Mercury.

Planets like Earth and Mars were large enough not split apart...

And big enough to generate heat in their rock and metal cores.

Volcanoes spewed out gases into new atmospheres...

Hydrogen and oxygen become liquid water...

Comets deliver ices and organic molecules from farther out in the solar system.

Just a few hundred million years after Earth formed, life began-as we can see in fossil stromatolites.

4 centuries ago, Galileo turned a telescope to the heavens, and discovered craters on the moon and sunspots on our local star.

One century ago, the American, Robert Goddard, began experiments in rocketry...

50 years ago, the space age began... and German, Russian and American engineers built the machines that would take humans into orbit.

Now we have tools like "Pathfinder" to explore our solar system, and can share in the exhilaration of seeing new worlds.

So, here's our cosmic address...

We orbit an average, yellow-dwarf star, which we expect to keep burning for another 5 billion years.

Our star is one of about 100 billion stars-that's one followed by 11 zeroes-in a vast spiral we call the Milky Way Galaxy.

The Milky Way, in turn, is one of 30 galaxies held relatively close together by gravity, known as "the local group."

But the Milky Way is but one of perhaps 100 billion galaxies in the known universe...

And in that vastness of space and time, we're beginning to discover that our solar system is not alone.

Chris Chyba
Carl Sagan Chair for the Study of Life in the Universe
SETI Institute & Stanford University

When we look at our solar system, we see a tremendous diversity of worlds. They all look so different from one another, and why, why should that be? A lot of it seems to have to do with how big the world is.

How big a world is when it forms depends on how many planetesimals it accretes, how many things that look like asteroids and comets collect together. And once a world starts accreting, it tends to run away and gather up everything in its vicinity.

So worlds that really ran away, like Jupiter, not only gathered up the planetesimals like asteroids and comets, but they got big enough fast enough to haul in a whole lot of hydrogen gas before that material was lost from the solar system.

Worlds like the Earth didn't get that big that fast and they're formed almost entirely of rock.