The Story of the Universe and Me: Where Did I Come From?
Part 2: The Solar System
Around five billion years ago, an average-sized white star swelled from the dust of a barred spiral galaxy. From the disc of remains that surrounded it, smaller bodies pulled together and fell into line around it, until it was orbited by a swarm of planets, from gas giants to tiny, rocky worlds. Because the temperature closer to the star was quite high, only rocky planets formed there, while further out it was cold enough for ices to remain solid and grow. Each of these planets struggled for dominance, disrupting and colliding with each other, smashing each other to pieces and pushing opponents away into lonely deep space. A particularly titanic specimen, which humans would much later name Jupiter, swept through the inner orbits with uncaring inertia, absorbing or tossing aside dozens of young planets before being pulled out to a safer distance.
Of the few that remained, one particular molten ball had grown to be the largest of the rocky inner worlds. Its surface was still far from hospitable, but it was not done yet. One of the planet’s smaller rivals careened into it, smashing itself to smithereens and knocking a considerable chunk from its larger brother. Some of the rubble from this collision remained in orbit around the large planet, and, still hot from its undignified ejection, pulled itself into a remarkable spherical companion, swinging around in the planet’s wake. You might be able to see it now if you look out the window, gazing down from the night sky .The planet also rounded itself back into a rough sphere, and became an object familiar to everyone reading this.
After some time, the planetary chaos settled into order, with each survivor having carved for itself a hard-won neighbourhood to call its own. There were eight of these largest bodies, and a litany of smaller ones. Orbiting closest to the star was the tiniest planet, named Mercury. Next was Venus, a planet clad in dense cloud. Next was the planet we mentioned before, which, among its many names, we now call Earth. Further out was Mars, not yet as dry as it would later become. Outside Mars’ orbit was a collection of fragments left over from the formative stages, along with a body not quite large enough to be called a planet: Ceres. Further still was Jupiter, a gassy colossus with a harem of satellites large enough to be planets of their own standing, but which had the misfortune to be pulled into the allure of the king of planets. Next was Saturn, a gas giant with a family of its own and a brilliant disc of water ice particles wrapped around its equator. Beyond him was Uranus, and further still Neptune, cold worlds of ice and gas. On the distant edges of the system were tiny members, embedded in a belt of ice and rock. These were Pluto and its twin Charon, Makemake, Haumea, Eris, and Sedna.
The solar system had become the collection of objects that we see today when we look into the night sky. But Earth, our future home, remained a hot, violently volcanic, inhospitable world.
To be continued!