Mercury has a daytime temperature of about 430 Celsius and a nighttime temperature below -170 Celsius what is the best explanation?

Answer 1

It has no atmosphere, so the side of the planet facing the sun is baked and the side of the planet away from the sun is frigid.  All planetary bodies that lack an atmosphere experience this wide temperature discrepancy.  An atmosphere (which provides wind currents and thermal insulation) more evenly distributes heat around the planet or moon or whatever.

Answer 2

Mercury's extreme temperature difference between day and night is due to its thin atmosphere that cannot retain heat. During the day, the lack of atmosphere means the surface absorbs a lot of heat from the sun, leading to high temperatures. At night, the absence of insulation causes the surface to rapidly lose that heat, resulting in very cold temperatures.