In 2012, NASA's MESSENGER spacecraft discovered water ice in the craters around Mercury's north pole where regions may be permanently shaded from the heat of the sun.

Mercury is too small and hot for its gravity to retain any significant atmosphere, but it does have a tenuous surface-bound exosphere containing 42 percent oxygen, 29 percent sodium, 22 percent hydrogen, 6 percent helium, 0.5 percent potassium, with possible trace amounts of argon, carbon dioxide, nitrogen, xenon, krypton and neon.

The Babylonians named the planet Nabu after the messenger to the gods in their mythology.

Craters on Mercury are named for artists, musicians, painters, and authors who have made important contributions to their field.

Scientists at Boston University's Center for Space Physics studied the bright yellow-orange light emitted by the sodium atoms in Mercury's tail and discovered the tail, previously detected to 15 times the radius of Mercury, actually extends more than 100 times that distance, or 1.6 million miles from the planet.

The axis of Mercury has the smallest tilt of all the planets in our Solar System, resulting in a lack of seasons on its surface.

According to measurements taken by Mariner 10, Mercury's magnetic field is about 1% the strength of Earth's.

In 2012, a rare green rock was collected in the Moroccan desert that scientists believe is the first meteorite from Mercury to be found on Earth.

MESSENGER, launched in 2004, orbited Mercury over 4,000 times in four years before exhausting its fuel and crashing into the planet's surface on April 30, 2015.

The tiny planet is made up of a single continental plate over a cooling iron core.