Mercury is the smallest, innermost, and fastest planet of our solar system and was created about 4.5 billion years ago. Its orbit of the sun takes around 88 days, the shortest of all the planets in our Solar System. Because it orbits so close to the sun, Mercury is often lost in the sun's glare and is hard to see from Earth. 

Mercury is named Mercury by the Romans, as they name all the planets they know after the Roman gods. Mercury is the fastest planet in the solar system, so it was named after the fastest Roman god.

Mercury is classified as a terrestrial planet as its surface is scarred with craters and volcanoes. Mercury has a silicate crust, a silicate mantle, and a nickel-iron core. The metallic core has a radius of about 2074 kilometers, and its crust, or mantle, is only about 400 kilometers thick.

Being the Solar System's smallest planet, Mercury has a diameter of 4,878 kilometers, which is only slightly larger than our moon, which has a diameter of 3474.2 kilometers.

Mercury's average distance from the sun is 57,909,227 kilometers and takes only 88 days to orbit the sun once. Mercury spins slowly on its axis, so one Mercury day is about 58.6 Earth days long.


Mercury's axis has only a 1/30 degree tilt, so the sun shines directly on the equator, making it devilishly hot during the day, and horrendously cold during the night. The cold temperature is because Mercury has no atmosphere to hold on to the heat from the sun. Temperatures can range from 427 to -173 degrees celsius. 

Rather than an atmosphere, Mercury has a thin exosphere of atoms battered by the solar wind and hitting meteorological effects from its crust. The exosphere of Mercury consists primarily of nitrogen,  sodium, hydrogen, plutonium, and potassium.

Mercury's surface is like our moon, having many craters and volcanoes, although it stopped being volcanically active 3.5 billion years ago. Mercury also has one of the Solar System's biggest craters, called the Caloris Basin. Its diameter stretches 1,550 kilometers. It was created about 400 million years ago when a giant asteroid slammed into the planet. 

Mercury's surface would appear to be dark-greyish to the human eye, and this is because of particles of rock crushed by comets and asteroids striking the planet.