Artwork showing the planets orbiting the sun (from inner to outer): Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
If you've ever stared at a model of the solar system, you'll observe that the sun, planets, moons, and asteroids all appear to be in the same plane. But why is it the case?
To answer this issue, we must go back to the origin of the solar system, roughly 4.5 billion years ago.
According to Nader Haghighipour, an astronomer at the University of Hawaii at Manoa, the solar system was essentially a vast, spinning cloud of dust and gas back then. One astronomical unit (AU) is the average distance between Earth and the sun, or about 93 million miles (150 million kilometers). According to Haghighipour, the cloud grew so large that it began to collapse and shrink under its mass, even though it was only filled with dust and gas molecules.
The revolving cloud of dust and gas flattened as it began to collapse. Consider a pizza chef launching a rotating slab of dough into the air. The dough grows as it spins, but it gets progressively thin and flat. That's what occurred to the solar system in its infancy.
Meanwhile, all those gas molecules in the core of this ever-flattening cloud became so compressed that they heated up, according to Haghighipour. Hydrogen and helium atoms merged under extreme heat and pressure, igniting a billions-of-years-long nuclear reaction that resulted in the birth of a young star: the sun.
Picture Showing Flat solar system.
The sun continued to grow for the next 50 million years, gathering gas and dust from its surroundings and releasing waves of extreme heat and radiation. The rising light gradually cleared a donut of space around it.
The cloud continued to collapse as the sun grew brighter, generating "a disc around the star [that] becomes flattered and flatter and expands and expands with the sun at its core," according to Haghighipour.
The cloud eventually grew into a flat structure termed a protoplanetary disc that orbited the young star. The disc was hundreds of AU broad and a tenth of that thickness, according to Haghighipour.
The dust particles in the protoplanetary disc softly whirled around for tens of millions of years after that, occasionally colliding. Some of them even stayed together. Those particles became millimeter-long grains, and those grains became centimeter-long pebbles, and the rocks continued to smash and stick together over millions of years.
Most of the material in the protoplanetary disc eventually clumped together to form massive objects. Some of these objects got large enough to be developed into spherical planets, dwarf planets, and moons by gravity. Other things, such as asteroids, comets, and some tiny moons, become oddly shaped.
Despite their various sizes, these things remained mainly on the same plane, where their construction materials originated. That's why the solar system's eight planets and other celestial bodies orbit at nearly the same altitude even now.
GLIMPSE from Upcoming Article:
Why are Galaxies of different shapes?
You can see stars from hundreds of billions of galaxies if you look up into the night sky. Some galaxies, like our own Milky Way, are spinning blue discs, while others are reddish spheres, deformed, clumpy messes, or something in between. What is the significance of the various configurations? It turns out that the shape of a galaxy can tell us a lot about what happened in its ultra-long life.
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