The planet known for its extreme surface temperature variations is Mercury. Being the closest planet to the Sun, Mercury experiences temperatures that vary drastically between day and night. During the day, surface temperatures can reach up to 800 degrees Fahrenheit (427 degrees Celsius), while at night, they can plunge to about -330 degrees Fahrenheit (-201 degrees Celsius). This extreme temperature variation occurs because Mercury has a very thin atmosphere that cannot retain heat. These conditions make Mercury an inhospitable world, yet its unique characteristics are of great interest to scientists studying planetary formation and dynamics.