Mercury Mercury has a diameter of 4879km at the equator. Mercury has a mass of: 3.3022x1023 kg Revolution around the sun in Earth years: once every 66 days Rotation time in hours: 24 hours Composition of planet and atmosphere: Who discovered it: the Romans.
Venus Diameter at equator: The equatorial diameter is about 12,104 miles, or about 95% of Earth's. (More precisely 12103.6 km.) Mass:4.867E24 kg Revolution around the sun in Earth years: takes 243 days to turn once on its axis, and it takes almost 225 days to travel once around the Sun in orbit. Composition of planet and atmosphere: Its surface is covered with lava flows, quake faults and impact craters. Venus has abundant small volcanoes and long lava flows. Venus has cool clouds and an extremely hot surface. Venus has a composition similar to that of basaltic volcanic rocks found on Earth. It has a thick, poisonous atmosphere of carbon dioxide and sulfuric acid.