Mercury (Planet)
Mercury is the first planet from the Sun. For a planet in the solar system, it's very fast, taking only 87.9691 days to go around, that's about half an Earth year. But as it is so close to Sun much of the time it is often hard to spot when observing from Earth.
image of Mercury from the MESSENGER spacecraft. image:wikipedia
Images of vast lava plains taken by the MESSENGER spacecraft (such as shown here) have demonstrated that Mercury was indeed volcanically active in the past. image: wikipedia/NASA
Orbit Basics
Distance from sun: between 69,816,900 and 46,001,200km
Orbital period (it's year) 87.9691 days
Animation comparing Mercury and Earth around the sun. image: Esquembre/wikipedia
#mediaviewer/File:Mercuryorbitsolarsystem.gif){kind=link}
Planet basics:
▪ Type of planet: rocky/terrestrial
▪ Length of day: 58.646 Earth days
▪ Average radius: 2,439.7 ± 1.0 km
▪ Mass: 3.3022×1023 kg or 0.055 Earths
▪ Surface gravity: 0.38 g
▪ Surface temperature: -173 to 427°C
▪ Atmosphere: trace
▪ Atmospheric composition:
▪42% molecular oxygen
▪29.0% sodium
▪22.0% hydrogen
▪6.0% helium
▪0.5% potassium
▪Trace amounts of argon, nitrogen, carbon dioxide, water vapor, xenon, krypton and neon
Further reading/Reference:
Solar system exploration: Planets: Mercury: Facts and Figures [NASA]