Our Solar System. Our own little corner of the Cosmos. Our own little oasis of light, and heat, and matter, in the limitless dark, and cold, and emptiness of space. Beyond our Solar System there is virtually nothing, for a very long way. The nearest star, Proxima Centauri, is over four light years away, and it may as well be four million. The fastest spacecraft we have would take 68,493 years to get there. Someday, we may develop the technology to traverse the great distances between stars, but certainly for any foreseeable future, our Solar System is all we have. We are trapped here by time and the laws of physics. But not to despair. Our solar neighbourhood is a very big, very busy place, with a lot of potential, including the very real possibility of finding extraterrestrial life on the moons Europa and Titan, or even still on the planet Mars. Exploring the planets and moons of our solar system is going to keep us busy for a very long time.
It all started more than five billion years ago. In one of the arms of a great spiral galaxy that came to be known as the Milky Way, about two thirds of the way out from the center, a few scattered atoms and molecules began to congregate. Gases formed. Microscopic bits of interstellar dust wandered into the mix. Forces of mutual attraction - the beginnings of gravity - began to work, drawing more and more material together.
It took a very long time, but eventually a huge cloud of gas and dust formed. When it got to be many billions of miles across, it began to take on a life of its own, heating up, and rotating. An intense gravity well formed at the center that pulled everything inwards. The more material pulled into the center of the cloud, the denser it became, and the more gravity and heat was produced, until finally the density and the heat became extreme enough to finally ignite, and a star - our Sun - was born.
99.8% of the cloud was consumed in the birth of the Sun. The 0.2% that was left over formed a protoplanetary disk, which ultimately consolidated into the planets and moons of our solar system, and all the thousands of asteroids and comets.
The image below is an actual photograph of a protoplanetary disk in the Great Orion Nebula, captured by the Hubble Space Telescope.
The photo composite below shows all eight planets in their proper order from the Sun, and accurately shows their sizes, relative to each other and to the Sun. You can easily see how the huge mass of the Sun contains almost all of the matter in our solar system, and how small the planets are in comparison, especially our tiny little blue/white home, Earth.
Obviously, the distances in the above image are not to scale. The planets in our solar system are actually separated by vast distances.
If the Sun was only one inch (2.54cm) in diameter, Earth would be the size of a small grain of sand almost 10 feet (3 meters) away. Giant Jupiter would be a large grain of sand almost 50 feet (16 meters) away. Uranus would be a medium sized grain of sand 170 feet (57 meters) away. And believe it or not, poor little I-was-once-a-planet Pluto would be little more than a speck of dust, 350 feet (118 meters) away from our little one inch Sun.
The diagram below shows the relative distances of all the planets from the Sun, and from each other. If their sizes were to scale as well, they would all be too small to see. Our solar system is a very big, lonely place, and like the Universe itself (as far as we can detect), mostly cold, empty space.
You can see how the four small solid planets of the inner solar system are all clustered relatively tightly around the Sun, while beyond the asteroid belt, the four giant gas planets of the outer solar system are spread very far apart, and are a very long way from the warmth and light of the Sun.
Below is an orrery, a real time representation of the relative positions of the planets in our Solar System. Green orbital segments are slightly below the orbital plane (ecliptic), and blue segments slightly above. An orrery can be a good tool for improving our perception of the solar system and our place within it. It helps our mind's eye add the crucial third dimension, and we can understand how, when viewed from Earth, the other planets sometimes appear close together, when they're not close together at all. And the next time we look up at the wandering planets in our sky, all lined up along the ecliptic, the solar system we live in becomes much more real.
Beyond the planets of our Solar System lies the Kuiper Belt, a region full of chunks of icy debris, some of which are large enough to be classified as dwarf planets, including the former planet Pluto.
Beyond the Kuiper Belt, the gravity of the Sun is not strong enough to keep the chunks of ice and rock that reside there in the same plane as the planets, so that they spread out into a sparsely populated sphere, or bubble of debris, referred to as the Oort Cloud. When a piece of this debris is disturbed by changing gravitational forces inside or outside our Solar System, and it begins to fall toward the Sun, a comet is born.
Getting to know our solar family starts with the grand patriarch himself, the living, breathing maestro at the centre of it all, the one who keeps us all together, and provides us with the sustenance of life - a star called Sol...