Question

Why does Mercury's surface temperature vary so much from day to night

Answer 1

Due to Mercury's closeness to the sun, The temperature will vary. The temperature in Daytime will most certainly be very hot since it's facing the Sun and in nighttime, the temperature will hit far below 0.

Answer 2

The atmosphere is really thin of mercury compared to Earth so it cannot retain solar. This planet is also a lot closer to the sun as well. Because of its elliptical orbit, it passes by the sun at diffrent times.