How hot is Mercury? Well, during sunlit hours, it’s hotter than a Florida beach in July, that’s for sure, with temperatures rising to over 800 degrees Fahrenheit. However, after the sun sets, temperatures can drop to nearly 280 degrees below zero, and scientists believe that water ice might even form in craters. The MESSENGER spacecraft’s image below shows Mercury’s north polar region, indicating maximum biannual temperatures by coloring hotter temperatures in red and colder ones in purple.