The inner planets, also known as the terrestrial planets, are the four planets that are closest to the Sun in our solar system. They are:
1. **Mercury:** The closest planet to the Sun, Mercury is small and rocky, with extreme temperature variations between its scorching hot days and freezing cold nights.
2. **Venus:** Often referred to as Earth's "sister planet" due to its similar size and composition, Venus has a thick atmosphere that traps heat, making it the hottest planet in our solar system.
3. **Earth:** Our home planet, Earth is the only planet known to support life. It has a diverse range of ecosystems and abundant liquid water on its surface.
4. **Mars:** Also known as the "Red Planet," Mars has a thin atmosphere and a cold, desert-like surface. It has attracted interest for its potential to host microbial life and the possibility of future human exploration.
These inner planets are primarily composed of rock and metal and have solid surfaces, distinguishing them from the outer gas giants like Jupiter and Saturn.