- The second planet of the solar system, and the closest in size to the Earth, 82 per cent as massive as the Earth. Venus orbits the Sun in 225 days, at an average distance of 0.72AU (108 million km), and has no satellites. Venus is swathed in clouds and has a high albedo, so that it can outshine anything in the sky apart from the Sun and Moon, reaching a magnitude of –4.4. Because of its nearness in mass and size (a radius of 6,050km to the Earth’s 6,378) to the Earth, Venus was long regarded as the Earth’s ‘twin’. But space missions to Venus have shown that it bears little resemblance to the Earth in terms of surface conditions – which is just as well for us. Its surface temperature can be over 700K. Venus rotates on its axis in a retrograde direction every 244 days. Its atmosphere is some 400 km deep and has a complex structure and wind systems. It contains large amounts of sulphur in chemical compounds and in elemental form, as well as nitrogen, rare gasses and carbon dioxide. Water is rare but there is a theory that it might once have been abundant. Atmospheric surface pressures on Venus run up nearly 100 times that at sea level on the Earth. The surface of Venus has plains, highlands and rift valleys, which have been mapped by radar (Magellan). Almost all our information about Venus has been obtained by spacecraft, especially the close radar mapping carried out by Magellan and information from probes sent into the planet’s atmosphere and onto its surface by parachute from US and Soviet spacecraft, mainly in the Venera series. Venusian surface features are named mainly in honour of real, mythological and fictional women.