The first planet in our Solar System is Mercury. It is the closest planet to the Sun and is characterized by its small size, extreme temperature fluctuations, and rocky surface. Mercury has a very thin atmosphere, which cannot retain heat, leading to scorching temperatures during the day and freezing conditions at night. The planet has numerous craters, which are evidence of its rocky history and lack of geological activity. Additionally, Mercury's rapid orbit around the Sun takes only about 88 Earth days. Despite its proximity to the Sun, Mercury remains one of the least explored planets, with only a few missions, including NASA's MESSENGER probe.