The planet closest to the sun is Mercury. However, it's not the hottest planet in our solar system. That title belongs to Venus.

Here's why:

* Mercury's proximity: Being the closest planet to the sun, Mercury receives the most direct sunlight and solar radiation.

* Lack of atmosphere: Mercury has a very thin atmosphere, which means it doesn't have much to trap the heat it receives. Most of the heat is radiated back into space.

* Venus's thick atmosphere: Venus has an incredibly dense atmosphere composed mostly of carbon dioxide. This atmosphere acts like a massive blanket, trapping the sun's heat and creating a runaway greenhouse effect.

* Surface temperatures: As a result, Venus's surface temperature can reach a scorching 867°F (464°C), making it the hottest planet in our solar system.

So, while Mercury is closest to the sun, Venus's thick atmosphere makes it the hottest.