Mercury, the planet closest to the sun, is the warmest planet in our entire solar system.

This is false! Even though Mercury is the closest planet to the sun, Venus is actually the warmest planet. Venus has a very thick atmosphere, full of gases, that acts like a super-blanket. This blanket traps the sun's heat, making the temperature on Venus much higher, even warmer than on Mercury, which has almost no atmosphere to hold onto heat.