Earth is in a structure a few light years across. This is the Solar System and it has a lot of mysteries and wonders to explore.
The Quantities of Celestial Bodies
The Solar System is a huge family because it has literally trillions of objects so we’ve just scratched its centre. We know a star, 8 planets, 3,661 comets and 991,905 asteroids according to NASA as of August 18, 2020. But well, we only know a tiny fraction of those. Although large bodies are mostly found in the distant past, we might find one today.
We haven’t explored more than 1% of the space in the Solar System yet. There might be a planet in the outskirts in the Solar System, and the unobserved Oort Cloud has a lot of comets, it might add up to more than the entire Earth. If they somehow collided, a super-Earth would form and the system will lose one of its features. The comets’ orbits take so long that they might’ve never visited the inner Solar System since the existence of humanity.
Image Source: solarsystem.nasa.gov
Sun
Sun is the central star of the Solar System, and dominates the gravity of the system. It accounts for more than 99% of the Solar System’s mass, and that’s a solar mass, which is used for calculating a star’s mass. It is a G2 yellow dwarf star, which is quite common in the cosmos. Its temperature is 5,778 K, 20 times hotter than Earth. There are sunspots on Sun, which are cooler places on the surface because of Sun’s magnetic field. By the way, Sun’s magnetic field is so powerful that it acts like a shield of cosmic rays, hundreds of astronomical units wide.
The Planets and Moons
There are 8 planets in the Solar System. The inner 4 are small rocky ones and the outer 4 are Neptunian and Jovian gas giants. Mercury is the smallest and the closest planet to Sun. Venus is the hottest planet and along with Mercury, they have no moons. Then, Earth is the only planet that harbours life and it has a large moon. Mars is the red planet because of iron oxide on its surface.
For the outer planets, Jupiter is the largest planet with 79 moons. It has a gigantic storm called the Great Red Spot. Saturn is a ringed planet with 82 moons. Next, Uranus and Neptune are similar Neptunian planets with a blue colour due to methane in their atmospheres.
Let’s talk about moons. Io is the most volcanic object in the Solar System and Europa has a deep ocean underneath its surface. Enceladus has plumes that spray out organic molecules and Titan has lakes, the second in the system after Earth. It also has an atmosphere, thicker than Earth’s.
Formation
The Solar System formed about 4.5 billion years ago when it was born in a star cluster. It started as a flat disk of materials of mostly hydrogen and helium. Then, most of the mass clumped into the centre to form Sun. It is massive enough for hydrogen to fuse.
Next, the rest of the matter, accounting for less than a percent, formed the planets. There are probably 5 gas clumps that formed Jupiter, Saturn, Uranus, Neptune and the unconfirmed Planet 9. The cosmos is rich in hydrogen and helium so they are huge. Planet 9 has a mass of about 10 Earths and Jupiter has about 318! They are also spinning fast because the gravity of the sub-nebula was very powerful that it orbits the centre quickly.
After that, the rocky materials made of heavier elements such as iron, nickel and sulphur collided with each other. As they crash, they create larger objects. Then, they become very frequent because of the gravity of the large planet and that helps it to grow. Finally, the planets ran out of materials to grow and start being the size it is now. The rocky material that is left in pieces, unable to form a planet, are called asteroids.
The Grand Tack Hypothesis
The Solar System is unlike any other system we’ve found. There are 4 main features: It is a place full of life, nothing is completely inside Mercury’s orbit, there are no super-Earths and hot Jupiters there, and Mars is very small after the 2 large rocks. Why it’s so special? Well, a theory can explain all of that. It is the Grand Tack Hypothesis.
First, Jupiter formed and migrated closer to Sun due to the interaction with the disk material. When it got close to where Mars is now, it stole the materials to form Mars, either eating it or throwing it into a farther region. The movement also relatively enriched the position of Earth and Venus. Also, its massive gravity kicked them to Sun and thrown it into an eccentric orbit. Long-period comets might originate there.
After a number of effects take place, Saturn formed and trapped Jupiter into a resonance. Then, it migrated outward and stopped where it is now. As said before, it limited the material available for the terrestrials. That prevented Earth and Venus to be super-Earths and is a reason that life exists on Earth. So Jupiter shaped the Solar System into this weird, habitable state.
The Effects
Then, when the comets spread throughout the Solar System, many bodies including Earth use their gravity to catch them. That’s why Earth, Europa, Enceladus and many other celestial bodies have water. Also, if Jupiter didn’t shape the system, Earth, the perfect planet for life might not be in the habitable position!