While it's true that Mercury is the closest planet to the sun, it's not the hottest planet in our solar system. That title goes to Venus.

Here's why:

* Venus has a thick atmosphere: Venus has a very dense atmosphere composed mainly of carbon dioxide, which traps heat through a process called the greenhouse effect. This trapped heat significantly raises the surface temperature, making Venus much hotter than Mercury.

* Mercury has no atmosphere: Mercury has a very thin atmosphere, meaning there is little to trap the sun's heat. This allows the heat to radiate back into space, resulting in a lower overall temperature compared to Venus.

So, while Mercury is the closest to the sun, it's Venus's thick atmosphere that makes it the hottest planet in our solar system.