Mercury is the planet closest to the Sun. It is a rocky planet (like Venus, Earth, and Mars) and not a gas planet (like Jupiter, Saturn, Uranus, and Neptune). It is named after Mercury, the Roman messenger of the gods.
Size of Mercury
Of the nine regular planets in the solar system, Mercury is larger only than Pluto.
Movement of Mercury
When Mercury is closest to the Sun, it is 46 million km away from it. The farthest that Mercury can go from the Sun is 70 million km. (Note: The closest and furthest point of a planet from the Sun are called the perihelion and the aphelion respectively.)
Odd Mercury Facts
Mercury's path around the Sun (i.e. orbit) is like a highly flattened circle. Also, its rotation is a bit erratic due to its proximity to the Sun. Hence, if one were on the surface of Mercury, one would see the Sun rise and expand gradually. When the Sun would reach the highest point in the sky, it would stop for some time, reverse direction and then resume its earlier path. And while this was happening, the other stars in the sky would be seen moving rapidly and steadily along the sky. On different points of Mercury's surface, the Sun's movement would be different!
Temperature - Tough to be Cool on Mercury!
Of all planets, Mercury has the most wildly varying temperature ranging from -180 degree Celsius to 426 degree Celsius.
Atmosphere of Mercury
Being close to the Sun, the atmosphere of Mercury is constantly exposed to streams of particles erupting from the Sun. Hence, the elements in the atmosphere of Mercury are constantly blasted into space and more particles from the surface of mercury come up into its thin atmosphere.
Gravity on Mercury
The gravity of Mercury is about one-hundredth that of Earth.
Satellites of Mercury
Mercury has no moons.
Mercury is sometimes visible to the naked eye as an evening object near where the sun has set, or as a morning object where the sun will rise. The ancient Greeks called the evening star (i.e. Mercury) Hermes and the morning star (again Mercury) Apollo, believing them to be different objects.
Surface of Mercury
The most conspicuous feature on the surface of mercury is Caloris Basin - a crater 1300 km wide. It is one one of the largest impact craters in the Solar System. The impact that created this crater was so strong that it created large rocky ridges even on the the other side of plane mercury!
• Average distance from the Sun: 58 million km, i.e. about one third the distance between the Sun and Earth.
• Length of a year: 88 days
• Rotation period: 58.65 days
• Average speed of travel in orbit: 48 km/s
• Diameter: 4,878 km, i.e. about one third the size of earth.
• Number of observed satellites: 0
• Mass: 3.30 x 1023 kg, i.e. about 5% the mass of Earth
Astronomy Information Pages