re: #185 b_sharp

I’m not sure if anyone answered the question about the heat on Mercury.

The side facing the sun is hot enough to melt lead but the back side is as cold as the dark side of the moon because there is no atmosphere or ocean to transport the heat and Mercury always keeps the same side facing the sun.

It’s tidally locked.

Mercury is gravitationally locked to the sun, but not such that the same side always faces the sun. Per wikipedia:

Mercury is gravitationally locked and rotates in a way that is unique in the Solar System. As seen relative to the fixed stars, it rotates exactly three times for every two revolutions it makes around its orbit. As seen from the Sun, in a frame of reference that rotates with the orbital motion, it appears to rotate only once every two Mercurian years. An observer on Mercury would therefore see only one day every two years.