Mercury

When found:
Known since ancient times, around the 2nd millennium BC.

By who:
Ancient Babylonian astronomers.

Description:
Mercury is the smallest planet in our solar system and the closest to the Sun. It's a rocky world with a heavily cratered surface, thin atmosphere, and extreme temperature variations.

Distance from Earth:
Closest distance: approximately 48 million miles.

Length of Year & Day:
Year (orbital period): 88 Earth days.
Day (solar day): 176 Earth days.

Interesting fact:
Mercury has no moons and experiences temperatures ranging from -173°C at night to 427°C during the day due to its lack of atmosphere.

Like it's Finder:
Like the ancient Babylonian astronomers who were swift in their observations of the fast-moving stars, Mercury orbits the Sun faster than any other planet, completing a year in just 88 days.