How Did Our Solar System Form?

by Carson
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Credit: NASA's Eyes

Do you know how our solar system, the planetary system that we’re in, formed and evolved to its present configuration? What are the mechanics involved in it? Let’s find out in this article.

The Formation of Our Solar System

The Solar System, like other planetary systems, form from a free-floating cloud of gas and dust. Due to external forces like those in a supernova, the matter is crammed so close that their mutual gravitational pull becomes enough to keep the material close together. Their gravity attracts even more material that their combined gravitational pull becomes stronger. This forms a positive feedback loop where a clump of interstellar particles becomes increasingly massive.

At some point in this loop, a central gaseous object forms at the center of the planetary system. If it is of less than 13 Jupiter masses, it becomes a rogue planet wandering in the galaxy. If its mass is between 13 to 80 Jupiter masses, it becomes a brown dwarf that cannot fuse hydrogen but can fuse deuterium. Finally, if the planetary system accumulates more than 80 Jupiter masses, the central object becomes a star that can undergo nuclear fusion. The Solar System falls into the last category of this paragraph since the celestial object at the center of it, the Sun, is a star.

What about the residual matter around the central object? Some of them don’t fall into the star. Instead, they orbit the star in an accretion disk. There are some regions of higher pressure in the disk, coalescing into planets, asteroids, and other objects.

The Grand Tack Hypothesis

In the Grand Tack Hypothesis, Jupiter first formed at around 3.5 astronomical units (AU) from the Sun. It was surrounded by a cloud of gas and dust, which alters Jupiter’s orbit in the same way as gravity assists until it eventually reaches 1.5 AU from our star, approximately where Mars is today.

The clouds of gas and dust surrounding Jupiter settled down, bringing the inward migration to a halt. Eventually, for some reason Jupiter migrated outward, putting Jupiter similar to the position we know today.

An illustration of Jupiter’s trajectory in the Grand Tack hypothesis

This model explains some properties of the asteroid belt. Before the model came into existence, it was believed that Jupiter’s gravity kept the asteroid belt from becoming a small dwarf planet. However, according to this model, the small objects in the asteroid belt were perturbed by Jupiter when it passed through the asteroid belt to the inner Solar System and back, scattering the asteroids around in a way that prevented them from colliding to form a larger object.

It also provides the reason why Mars is much smaller than previous models of the evolution of the Solar System suggest. During Jupiter’s visit to the inner Solar System, it scatters the small rocks around where Mars is today, taking away resources that would have led to the formation of a larger planet.

The Nice Model

However, with the Grand Tack hypothesis alone, it was still unclear why Uranus and Neptune are so far away from the inner Solar System. These mysteries are explained by the Nice Model, which is very compatible with the Grand Tack hypothesis we discussed in the last section.

According to the Nice Model, in the first few hundred million years of our Solar System, Uranus and Neptune were much closer to our star than it is now. At that time, Jupiter and Saturn are nearly in a 2:1 orbital resonance, with Jupiter circling the Sun twice while Saturn completes one orbit. When Saturn crosses the 1:2 orbital resonance point, the gravitational interactions cause instability in the outer Solar System, moving Uranus and Neptune outwards while scattering matter around to close to its current configuration.

This model explains the abundance of Trojan asteroids of the gas giants. As the outer Solar System was unstable, there were more chances for asteroids to enter the Trojan region of the planets, thus orbiting our star with the planet. The chaotic situation of the Solar System at that time also explains the sudden increase in asteroid impacts when the Solar System should have been settling down, and most importantly, the orbits of Uranus and Neptune.

Conclusion

In this article, we’ve explained how the Solar System came into existence and how the Solar System has evolved. Remember that it is a complex process that scientists worldwide are still investigating. For more information on these aspects, please visit the websites in the references below.

References and Credits

  1. (2014, February 24). What’s the difference between a brown dwarf and a planet? Retrieved June 19, 2022, from https://astronomy.com/magazine/ask-astro/2014/02/brown-dwarf
  2. (2021, August 4). Neither Star nor Planet: A Strange Brown Dwarf Puzzles Astronomers. Retrieved June 19, 2022, from https://www.quantamagazine.org/neither-star-nor-planet-a-strange-brown-dwarf-puzzles-astronomers-20210804/
  3. (2011, August 19). Jupiter’s “Grand Tack” Reshaped the Solar System. Retrieved June 19, 2022, from https://astrobiology.nasa.gov/news/jupiters-grand-tack-reshaped-the-solar-system/
  4. (n.d.). The Grand Tack. Retrieved June 19, 2022, from https://www.boulder.swri.edu/~kwalsh/GrandTack.html
  5. (2018, April 24). The Nice Model. Retrieved June 19, 2022, from http://lucy.swri.edu/2018/04/24/Nice-Model.html
  6. (n.d.). The Nice Model. Retrieved June 19, 2022, from http://www2.ess.ucla.edu/~jewitt/kb/nice.html

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