Why Mercury has extreme days and nights

Slide 1

Mercury’s days are hot and its nights very cold

Mercury is the planet closest to the Sun. Its sunlit surface becomes extremely hot, while the long night allows exposed ground to become very cold.

Slide 2

Its thin exosphere cannot redistribute much heat

Mercury has an extremely thin exosphere instead of a substantial atmosphere. It cannot redistribute and retain surface heat as Earth’s air does.

Slide 3

Three rotations in two orbits create a long sunlight cycle

Mercury rotates three times for every two trips around the Sun. Rotation and orbital motion combine to produce a very long cycle of sunlight and darkness.

Slide 4

Radar disproved the permanently sun-facing picture

Astronomers once thought Mercury kept one side permanently toward the Sun. Radar measurements showed that the planet does rotate relative to the sunlight.

Slide 5

Permanent polar shadows can still preserve water ice

Deep craters near Mercury’s poles can remain permanently shaded. Water ice can survive in these cold traps despite the planet’s proximity to the Sun.

Sources

• Mercury Facts

  NASA

• Mercury

  OpenStax, Rice University