There are many questions we’ve had about the universe since humans looked at the sky. Where did it all come from, and why are we here? Well, while we can’t dive into something quite so existential, we can explore one of the mysterious of our own stellar neighborhood. That is to say, answering the question “How did the solar system form?”
As you can imagine there are a lot of layers to this answer. Scientists and astronomers have been digging at the mystery for centuries, using observations from what we see in the night sky to discoveries on Earth. Since the conception of the question, there were multiple theories on how our solar system (and planet) came to be. Some believed the sun’s formation ejected all the necessary rocky material from its core, others theorized the planets were simply caught by the sun’s gravity.
Today, when astronomers dive into how the planets in the solar system form, they rely on the most commonly accepted theory: the Nebular Hypothesis. We talked briefly about this when discussing the age of the solar system, but here, we’ll get into it a bit more.
The Nebular Hypothesis
When discussing formation ideas and theories, this is where scientists begin. Astronomy is always leading to new discoveries, so this theory can change. It was originally proposed by Pierre Simon de Laplace in 1796, explaining how our system was formed and others in the universe.
It’s referred to as the Nebular Hypothesis, because the creation of a system starts in nebular clouds. Cloudy molecular material forms clumps in space, but unstable gravity eventually pulls these clumps together. The larger the clump, the more heat and gravity are produced, and throughout a sequence of millions of years, a proto-star is born.
When answering “how did the solar system form,” one answer is always certain: the need for a star. As the gaseous material rotates and clumps, the growing star eventually seeds it with heavier elements. Once the star erupts into life, it creates a domain of gravity to capture and rotate the surrounding nebular material. This material swirls together and, based on the elements present, can form either a terrestrial planet or gas giant.
All this material started to rotate, creating the stellar objects we’re familiar with today. From distant Neptune to the many moons of Jupiter, these were likely – at some point – molecular, nebulous matter.
Fascinating! So, in a nutshell, nebular matter condensed together to form a star. Why it starting clumping remains up to speculation. Some astronomers think a nearby astronomical event, like a supernova, caused a disturbance to “stir” the material together. The fact remains, once our star was born, everything else fell into place.
The process is far more complex than that, but it’s a general summary. Of course, this also begs the question: how did the planets in our solar system form?
That too is a fairly complicated answer, as it would require analyzing the evolution of each planet. We don’t have time to go over each in intricate detail, but, we can quickly discuss their general formation and origin.
To start, scientists estimate the solar system’s age (and also the planets/sun) is about 4.5 billion years old. They measure this in a variety of ways, such as observing the formation of other distant solar systems and taking measurements of decaying isotopes from meteorites. Those clue us in to a lot of things, like the material present when the system was forming itself.
As for the planet’s creation, remember all the dust from the nebula? Once they started to rotate, said dust accreted into clumps of material. The four rocky planets were hot enough that elements boiled together, leading to the creation of metal/rock elements. Those silicates were the only elements able to withstand the heat of the sun, and thus, the four terrestrial worlds Mercury, Venus, Earth, and Mars were born.
However, the gas giants were distant enough their icy formations and elements didn’t melt away, something astronomers refer to as the “Frost Line.” This lead to the planets we know as Saturn, Jupiter, Uranus, and Neptune, all of which contain elements like hydrogen, helium, and ammonia.
But what about Pluto? Astronomers now refer to objects like Pluto as a Dwarf Planet, planetoids which do not have their own unique orbit. That’s because dwarf planets like Pluto and Eris are near the Kuiper Belt and Oort Cloud. When discussing the solar system’s creation, you can’t leave out these important objects either!
The objects found in the Oort Cloud and Kuiper Belt are likely remains from our solar system’s violent origin, so far out they’re essential particles of icy-rock. Some astronomers speculate this is where water came from, that perhaps this material collided into Earth’s earliest days. Regardless, the farther out you go, the colder things get. Astronomers will likely discover more dwarf planets and other mysteries as they hunt for answers.
Wow! That’s a lot to take in, isn’t it? The processes we mentioned occurred over tens of millions of years, but astronomers – based on current information – believed this is how are solar system began.
- The Nebular Hypothesis is the most commonly accepted explanation about our solar system.
- Gas and nebular dust was clumped together due to an astronomical occurrence.
- A proto-star formed over millions of years and created the necessary temperature and gravity for planetary formation.
- Over more tens of millions of years, terrestrial worlds and gas giants formed, orbiting the new sun.
- Astronomers measure this through observations and taking data from decaying isotopes found in ancient meteorites.
Now you have a general idea of how it all started! When asking “how did the solar system form,” you can answer – with some confidence – from the perspective of the Nebular Hypothesis. There, of course, is a lot more to it than what we’ve described, but it’s the general map of how everything came to be.