Now, it’s time to go out of Earth and look further. We will look at the Solar System which consists of 1 star, 8 planets, millions of comets and billions of asteroids.
Sun’s profile
First, we will look at the only star in Solar System — Sun. It is a yellow dwarf. Its surface temperature is 5,778 K, almost 5,505 degrees celsius. It is a hot ball of plasma instead of a hot fireball. I will talk about stars in a future episode. Sun consists of 99.86% of the Solar System’s mass, which is the most massive object in the system. Sun’s mass is 1,989,000,000,000,000,000,000,000,000,000 kilograms, which is about 333,000 Earth masses. It is a whopping 1,392,684 kilometres across, it can fit 109 Earths! Its luminosity is 1 Solar Luminosity, which is used to determine the luminosity of other stars.
It is currently in the main sequence, which fuses hydrogen into helium. Each second, it fuses 620 tons of hydrogen to 606 tons of helium. That’s a whopping amount! That’s because the pressure in the Sun’s core makes it as hot as 15,000,000 degrees celsius, so hydrogen can fuse.
We will introduce Mercury, Venus, Mars and the Asteroid Belt in this episode, and other objects in a future episode.
Mercury’s profile
Mercury is the first planet from the Sun, and it is also the smallest one, the least massive one and the second-densest one in the Solar System. It has no atmosphere so temperature fluctuations are so extreme there that it can reach 440 degrees celsius at daytime while it reaches -180 degrees celsius at night time. It is about 57,909,050 kilometres from the Sun and it is tidally locked by Sun with an interesting spin-orbit resonance of 3:2, which means 3 days on Mercury is exactly 2 years.
Mercury has no celestial body in orbit. It has an orbital period of about 88 days and a rotational period of about 57 days. Its rotation is the second-slowest one in Solar System and its orbital velocity is the fastest since it is the closest planet to the Sun. Mercury also has the most elliptical orbit in the Solar System, which is clearly seen in a model.
Venus’s profile
Venus is the most similar to Earth in mass and size. Its mass is 80% that of Earth while its diameter is 95% that of Earth. But Venus is a pretty hostile environment. Its temperature reaches 460 degrees celsius due to the extreme greenhouse effect that’s happening on that planet, therefore, it is the hottest planet in the Solar System! Why there are extreme greenhouse effect is because it has a very thick atmosphere, 92 times denser than Earth’s, filled with carbon dioxide. Also, its atmospheric pressure crushed Venus landers as soon as they made it to the surface!
Interestingly, Venus’s day is longer than its year, with 243 days being its day and 225 days being its year! It also spins backwards, maybe since an asteroid hit it severely and changed its rotational direction. Like Mercury, it has no celestial body in its orbit. Its orbit is also the most circular one in the Solar System.
Mars’s profile
Since we’ve already talked about Earth, we will move on to Mars. Mars is the most Earth-like terrestrial planet in the Solar System but still uninhabitable. It is the second-smallest planet in the Solar System, with 53% the diameter of Earth and 10.7% the mass of Earth. Its atmospheric pressure is only 1% that of Earth. Although it is technically in the habitable zone, it has almost no greenhouse effect. So astronauts need special equipment to set foot on Mars.
Still, scientists think Mars was habitable in the past, and they are keeping track of evidence of liquid water appearing in the past by geological traces. It is a red planet because the iron on the surface turning into iron oxide.
Mars’s day is only 37 minutes longer than Earth’s and its year is 687 days or approximately 1.881 Earth years.
Asteroids’ profile
The Asteroid Belt is where most of the asteroids orbit the Sun. What are asteroids? Asteroids are small space debris that haven’t formed a planet or a dwarf planet yet, being in different shapes because the gravitational pull of the asteroids are uneven. Asteroids are mostly made of silicates, carbon or metal. Their size also vary from a meter to hundreds of kilometres!
Although there are millions of them in the main belt, they add up far under Moon’s mass. Their distance from the Sun vary from 2 astronomical units to 5.2 astronomical units. The furthest asteroids from the Sun that are near the main belt are Jupiter trojans. They are in a stable position of Jupiter to keep sharing its orbit. That does not represent Jupiter cannot clear them because their position never cross Jupiter’s position. Trojans work like this way. Earth has trojans too, but only one.