Mercury

Mercury is the smallest and closest planet to the sun in our solar system. It takes 87.97 Earth days to make a full orbit around the sun which is the shortest of all planets.

only two spacecrafts have visited Mercury: Mariner 10 which flew by in 1974 and 1975; and MESSENGER, launched in 2004, this spacecraft has orbited the small planet 4,000 times in over 4 years before using up all its fuel, and crashing into Mercury's surface on April 30, 2015. A third spacecraft, BepiColombo, is set to arrive at this planet in 2025.

Size and Distance
Coming in as the smallest planet with a radius of 1,516 miles (2,240 kilometres), Mercury is more than 1/3 the width of the Earth.

Mercury is 36 million miles (58 million kilometres) or 0.4 astronomical units (abbreviated as 'AU'). one AU is equal to the distance from the Sun to Earth. From the Sun, it takes 3.2 minutes for its light to reach Mercury.

Orbit and Rotation
Mercury's egg-shaped orbit takes as close as 29 million (47 million kilometres) and as far as 43 million miles (70 million kilometres) from the sun. This means that Mercury travels through space at nearly 29 miles (47 kilometres) per second, this is faster than any other planet in the solar system.

Mercury completes one rotation every 59 Earth days, but when its travelling its fastest through space, each rotation does not include sunrise or sunset. When the sun rises on Mercury, on some parts of the planet's surface it appears to briefly rise and set. The same process described happens at sunset as well. One full day-night cycle on Mercury (one solar day) is equal to 176 Earth days.

Structure
After Earth, Mercury is the second densest planet in the solar system. Its large core measures in at 1,289 miles (2,074 kilometres) which is about 85% of the planet's radius. Evidence may prove that it is partially molten, or liquid.

Formation
About 4.5 billion years ago, gravity pulled swirling gas and dust together to form a small planet which we know today as Mercury. Being known as a terrestrial planet, Mercury has a central core with a rocky mantle and a solid crust.

Kid-Friendly Facts
Mercury is the smallest planet in our solar system. It's the closest planet to the sun and a little bit bigger than Earth. Along with Venus, Earth and Mars, Mercury is one of the rockiest planets. Like our moon, Mercury is covered with craters. It doesn't have any moons and has a smooth atmosphere.

Compared to Earth, Mercury spins slowly, which means one day lasts a long time. A day on Mercury takes 59 Earth days to make one full rotation, but on Mercury, a year on this planet goes by really fast. To go around the Sun, Mercury must take 88 Earth days to complete its rotation.

Surface
Earth's moon closely resembles Mercury's surface, scattered by resulting impacts of craters and collisions with meteorites and asteroids. Some of Mercury's features, such as craters, are named after a deceased artists, musicians or authors including Dr Seuss and Alvin Ailey.

Large impact basins, including Caloris (960 miles or 1,550 kilometres in diameter) and Rachmaninoff (190 miles or 306 kilometres in diameter), were results of asteroid impacts on Mercury's surface in the early life cycle of the solar system. While the planet does contain smooth areas of terrain, there are also cliffs which measure in at hundreds of miles long and soaring up to a mile high. This terrain formed as the Mercury's interior cooled over the billions of years since the planet's formation.

Temperatures on the surface of Mercury are extreme, variations from hotness and coldness. Mercury's surface, during the day, can reach up to 430 degrees Celsius because the atmosphere can not retain the heat. During the night, however, the temperature cools to a jaw-dropping -180 degrees Celsius.

Inside deep craters, but only showing in regions of permanent shadow, Mercury may have water at its north and south poles. There it could be cool enough to preserve this water despite the scorching temperatures during the day.

Atmosphere
Instead of an atmosphere, Mercury possesses a thin exosphere made up of atoms blasted away by solar winds on the surface and striking meteoroids. The planet's exosphere is composed of 5 elements: oxygen, sodium, hydrogen, helium and potassium.

Magnetosphere
Mercury's magnetic field at the surface has 1% of the Earth's strength. Magnetic tornadoes are sometimes created that funnel the plasma wind down to the surface.

Moons
Mercury currently has no moons.

Human Life
Mercury's temperatures are too extreme for human life to colonise on. The characteristics of this planet make it very unlikely for organisms to adapt to.

Sounds
Sounds of Mercury captured by NASA's spacecraft BepiColombo