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A bunch of planets orbit a yellow star in a quiet suburb of the Milky Way galaxy. Over the past decade, our vision of our solar system has been completely revamped. Think of the solar system as an old-fashioned mafia crime family. The sun is the don. His quarreling children, the planets. Their story, like any good mob movie, is an epic tale of empire building, sibling rivalry, greed, and ultra-violence. The origin of the solar system was chaotic and violent. Planets colliding, planets even changing places.
Now, a shift in our understanding reveals a tale of tangled alliances between family members. Just think about how much our view of the solar system has changed. The planets used to be so far away from each other, and of course they had nothing to do with each other, and now the history is all about the interaction. So, the idea that everything is just its own world and doesn't interact is completely wrong. We like to think of astronomy as looking up, looking outward, away from ourselves. But the more we do that, the more we realize how connected we are to everything out there.
You probably have some material in your body from pretty much every world that ever existed in the solar system. Like any good mobster movie, our story starts with the humble rise of the godfather. In this tale, that's the birth of the sun. But exactly how that happens is a mystery. When we're trying to figure out how the solar system began, you know, we don't have a time machine. So, what can we use to find out about how it formed? The solar system has the answer. It's own time machines. Meteorites. Meteorites are pieces of the solar system from the distant past and they've remained unchanged since then. So, they're like little time capsules.
They're like fossils from before our solar system even formed. By studying them, we can really study what was happening, what was going on in the very early days of our own solar system. 2020 Scientists study ancient material trapped inside a meteorite found in Murchison, Australia. The Murchison meteorite contains tiny crystals called pre-solar grains that predate our sun. And trapped within them is evidence of the history of the formation of our solar system. The pre-solar grains are made up of elements like silicon that form inside giant stars. When these stars die, they blow out huge clouds of gas and grains of dust.
The term pre-solar grain doesn't sound very romantic, but actually, we might call those stardust because these materials are things that were made in stars that no longer exist. The Murchison meteorite contains grains from at least 46 different stars. What the Murchison meteorite tells us is that the material that came together that formed our solar system had its origination in dozens of different stars. These stars died and blew out all of these materials and then created this huge cloud of gas and dust called a nebula. The sources of the material in that cloud could come from one of a number of places. The material from lots of stars
atmospheres could be mixed in there. In the mix were the ingredients to build the solar system. But we don't know what triggered the gas and dust to form the sun. A 2020 study may have the answer. One of the coolest things we've discovered in the last couple decades about the Milky Way is there's a giant stream of stars that's stretching across virtually the whole sky. [snorts] These stars were not born in the galaxy. They're not from here. If not from our galaxy, then from where? We think these stars actually came from the Sagittarius dwarf galaxy which orbits the Milky Way.
Over 5 billion years ago, the Sagittarius dwarf galaxy wanders too close to the Milky Way. Our galaxy's powerful gravity drags Sagittarius towards it. The galaxies collide. As this is happening, the Milky Way is tearing Sagittarius apart, ripping stars out of it. This is truly intergalactic cosmological drama at play. This collision shakes up the Milky Way. When a body passes through the disc of our galaxy, it's going to set off ripples and that's going to compress the gas clouds and that's going to create star formation.
The Sagittarius dwarf smashing into the Milky Way is like dropping a boulder into a pond. It sets out ripples of density, and it disturbs everything in the galaxy, but it doesn't disturb everything equally. It causes some clumps of dust and gas to start accumulating together. The disruption in one galactic zip code leads to new activity in others across the Milky Way. The ripples trigger gas and dust left over from the dying stars to split into clumps, sparking a frenzy of star formation.
Look, if you were an observer, suddenly out of these little clumps of gas come bright ignition sparks, all at once. If you were to stand there long enough watching this stellar nursery, it might look kind of like a field at night with fireflies blinking on. Perhaps the sun formed in this starburst. The passage of the Sagittarius dwarf through our galaxy correlates in time to the formation and birth of our sun, so maybe our solar system came about as a result of the Sagittarius dwarf passing through our galaxy over 5 billion years ago. Of course, we don't know for sure if this is what triggered the formation of our sun, but the timing does fit.
4.6 billion years ago, part of the cloud seeded with material from dying stars grows denser until it gets so massive it collapses. As the gas cloud collapses, it gets hotter and spins faster and faster forming a dense core at its center. The core is the protostar that will later become our sun. The protostar drags in more and more gas and dust creating a region of material spinning around it called the protoplanetary disk. As the sun builds up more mass, it's getting compressed gravitationally. And so the core is getting hotter and hotter. The densities are increasing.
The new dawn, the head of our solar mobster family, immediately reveals a ferocious nature. Blasting out supercharged jets of radiation. The early sun was not the calm glowing orb that we see in our sky today. It was far more chaotic. It's sort of like in its toddler phase. It was acting up all the time. It has all of this energy that pushes material off of the surface and launches it into what we call the solar wind.
The blizzard of particles races out at over a million miles an hour. It smashes into the protoplanetary disk and blows the gas away. At the same time, the sun's core heats up to 18 million degrees Fahrenheit triggering the fusion of hydrogen into helium. And that releases a tremendous amount of energy that eventually works its way back to the surface of the star and comes out as light. Finally, the sun becomes the recognizable Sun that we see in our sky today. The Sun is now the Godfather, pulling the strings of the solar system.
The young Don's rise to the top triggers a power struggle with its willful children, the planets. It's a brutal fight for survival.
