Mercury is often thought of as a hot planet because it is the closest planet to the Sun. However, the truth is a bit more complex. During the day, temperatures on Mercury can reach blistering highs of about 800 degrees Fahrenheit (427 degrees Celsius). However, each night, the temperature can plummet to around -330 degrees Fahrenheit (-201 degrees Celsius).
This extreme temperature variation occurs because Mercury has a very thin atmosphere, which is unable to retain heat. As a result, the planet experiences intense heat during the day when it is exposed to sunlight, but loses that heat rapidly when the Sun sets. Therefore, while Mercury can be hot during the day, it is also extremely cold at night, making it both a hot and cold planet depending on the time of day.