Mercury is often thought to be the hottest planet in our solar system, but this can be a little misleading. While it’s true that Mercury has the highest temperatures among the planets, it isn’t constantly hot like Venus, which is the hottest planet overall.
The reason Mercury experiences such high temperatures during the day is largely due to its proximity to the Sun. Being the closest planet, it receives a lot of solar radiation, causing surface temperatures to soar up to about 800 degrees Fahrenheit (427 degrees Celsius) when the Sun is shining directly on it.
However, Mercury has almost no atmosphere to retain heat. This means that when the Sun sets, temperatures can plummet drastically, dropping to around -330 degrees Fahrenheit (-201 degrees Celsius) at night. So, while daytime temperatures are scorching, the lack of an atmosphere leads to extreme fluctuations.
In contrast, Venus has a thick atmosphere filled with carbon dioxide that traps heat through the greenhouse effect, resulting in consistent high temperatures of around 900 degrees Fahrenheit (475 degrees Celsius) on its surface. Thus, while Mercury can reach high temperatures, it also experiences extreme cold at night, making Venus the hottest planet overall.