Mercury

Mercury is the smallest planet in the solar system and is only half a millimeter in diameter here in the model. When we stand next to Mercury and look towards the Sun six meters away, it appears just as large as it would if we were actually standing on the planet.

The surfaces of Mercury and the Moon are remarkably similar. This is because both worlds lack an atmosphere (“air”). This lack of air is also why the tracks of the many meteors that have struck Mercury and the Moon over time have not been wiped away by winds and the forces of nature. As a result, the surfaces of these two celestial bodies are covered in impact craters of various sizes. To the human eye, the landscape is ash-grey and brown, streaked with bright dust lines from more recent meteorite impacts. 

In its interior, Mercury hides a massive iron core that makes up a staggering 85% of the planet's volume. As this core cooled over billions of years, the planet shrank dramatically. This caused the surface to crack, leaving kilometer-high cliffs across the otherwise flat plains. 

Mercury takes 88 days to complete one orbit around the Sun, while rotating on its own axis in 59 days. This leads to unusually long day-night cycles and extreme temperature shifts, but it also means that the planet completes two orbits around the Sun for every single sunrise seen from its surface. If you lived on Mercury, you could celebrate two birthdays every day. 

At its hottest, the planet reaches a temperature of 430 degrees Celsius, but at night, the temperature can plummet to -170 degrees Celsius. 

Mercury is one of the few planets in the solar system without moons.