Our Solar System is quite “young”, at least as far as solar systems go. Using radiometric dating, scientists were able to determine that most of its ingredients, including the sun and the planets, are just over 4.6 billion years old (while one of the oldest stars detected is a ripe 13.6 billion years old.) By comparison, humans have been around for a “mere” 200 thousand years, a barely noticeable spec in the vastness of Solar System’s lifespan.
The mass of the Sun is 1.989 × 1030 kg when all the planets combined are only 2.66 x 1027 kg.
Although Mercury is the planet nearest to the Sun, it’s actually only the second hottest planet, following Venus. Why? Mercury is tiny and doesn’t have any atmosphere, which under normal circumstances traps and holds heat. Any heat that Mercury receives from the sun quickly dissipates back into space. Venus on the other hand is very close in size to Earth and viewing it has been difficult due to a very thick atmosphere of carbon dioxide. This thick atmosphere, coupled with its close proximity to the sun, makes the surface of Venus hotter because the heat has a harder time escaping back into space.
You haven't left planet Earth as long as you're still within the bounds of Earth's atmosphere (or gone beyond the Kármán line.) Similarly, Sun has it's own version of the "atmosphere", called Heliosphere, which extends far beyond our solar system. It engulfs all the planets and is responsible for some amazing experiences both in space as well as here on Earth such as the wondrous Aurora lights.
- The inner planets (also known as terrestrial planets) are smaller and made primarily of rock and metal.
The outer planets can be further categorized into two sub-classes – gas giants and ice giants. These are much larger and further away from the sun:
- The gas giants primarily consist of lighter gasses, higher up on the periodic table (e.g. H and He.)
- The ice giants contain gases heavier than those that make up gas giants, e.g. O, C, N, S and located at the outer rim of our solar system.