It all begins with a star. When a star is born, it undergoes a gravitational collapse that leaves behind dust, clouds, and other planet-forming debris. This debris orbits around the star and is known as an accretion disk or a planetary nebula. The nebula is referred to as an emissions nebula once its components radiate enough heat to illuminate the gaseous dust cloud. The cloud thought to have formed our own solar system 4.5 billion years ago is referred to as a solar nebula.
Once you have a star and a nebula, the next step in the birth of a solar system involves the nebula’s collapse. Our solar nebula, according to the theory described in our text book, was probably so spread out that it required more than just gravitational forces to initiate its collapse. An example of an outside force large enough instigate this would be a nearby star explosion (specifically, the formation of a supernova.)
As the nebula collapses in on itself, several forces are at work producing various results. First, gravity pulls all of the particles in all directions inwards towards the center. As gravity pulls the nebula inwards, it begins to shrink and heat up. Most of the heat and density is concentrated in the center, which is where our sun formed. The solar nebula also spun and flattened into a disk as it heated up and collapsed in on itself. This disk is referred to as a protoplanetary disk. At some point, the extra gas is blown away, leaving only solid material in the nebula. These tiny particles of material that are leftover orbiting the star are what will eventually make up the planets, moons, and comets of the solar system.
The gravitational forces, forces caused by rotation, temperature, and the characteristic of being a flat plane each contribute to the formation of planets, moons, and comets. As the particles of material continue rotating, they collide with each other and begin to clump together, especially so at lower temperatures. The temperature drops the farther a particle is from the center of the nebula. After innumerable collisions, these clumps slowly gain more and more particles, and eventually they turn into comets, which smash into each other to become dwarf planets, which smash into each other to become larger planets.
The distance of each planet from the sun affects its composition. Mercury, Venus, Earth, and Mars were all close enough to the sun to develop into terrestrial planets, which are warm and have a solid, tangible surface. Jupiter, Saturn, Uranus, and Neptune (and Pluto) are all known as “Jovian” planets, which means that they are cooler, gaseous planets.
There are several pieces of evidence to support this theory of our solar system’s formation. The general motion and behavior of our solar system fits the bill. The planets rotate around the sun in a flat plane, with all planets and most of their moons going in the same direction. And all planets (except Venus) rotate in the same direction as their orbit. Research into other, similar solar systems throughout various stages of their development also supports this theory.
Scientists created the solar nebula theory (and continue to find clues on how our solar system was formed) by studying the various components of it. An article I found on spacedaily.com titled “How comets are born” explains how an in-depth study of Comet 67P/C-G reveals information on how our solar system came to be. The fragile, porous structure of this specific comet has lead the researchers to believe that the collisions of particles forming the comet happened at low speeds, since high speeds would have compromised its structure. Through spectral analysis of this comet, they have determined that the surface of the comet came into contact with very little or no water during its formation, and they discovered the comet is chemically comprised of carbon monoxide, nitrogen, hydrogen, and carbon. The presence of these elements leads the researchers to believe that the comet formed in cold temperatures. Researchers conclude that this comet and others like it must have formed slowly, over the entirety of our solar system’s existence, accumulating mass from leftover particles on the very outskirts of it. (Talk about living on the edge!)
This all relates back to the conceptual objective because the study gives us insight into how our solar system was formed. Dating the material that the comet is made of and determining its age helps us figure out the age of our own solar system. Testing its chemical composition unveiled remnants of ice, indicating that formation tempratures must have been freezing. Testing the chemical composition also tells us that the comet formed on its own, and not of something called TNO’s (trans-Neptunian objects.)
A comet building slowly in cold temperatures very far away from our star backs up the entire nebula-theory of solar system formation. The theory says that particles accumulated over many collisions over time, and that the temperature and speed of these rotating particles decreases as distance from the sun increases.
The article also mentions that the study forced scientists to reconsider how TNO’s formed, since some of these are as far out in the solar system as comets like Comet 67P/C-G, yet show evidence of being heated by short-lived radioactive substances while comets do not show any signs of being heated. After careful consideration, the researchers determined that TNO’s must have formed “rapidly within the first one million years of the solar nebula.” As you can see, the study of this one comet has provided the science community with an abundance of information on the formation of the solar system, which is why I chose to include this article in this blog post.
REFLECTION: I really liked this article because I find it fascinating how scientists are able to piece together the little information that they have in order to draw conclusions (or at least develop plausible theories for further research) on things they are still trying to figure out. I thought the study of this comet was really important because they found out a ton of information on the formation and chemical composition of comets, the approximate age of larger/more distant TNO’s, and the formation of our solar system, all from just from this one study.