Because the surface is hidden by sulphuric acid clouds, and the planet is similar to the Earth in size, astronomers speculated for many years that Venus might be a lush world full of life.
It is now thought possible that the Sun's heat boiled away early oceans on the planet triggering a planet-warming runaway greenhouse effect that turned Venus into a hellish place.
Photo: A false-colour view of Venus taken by the Galileo probe. This photo was coloured blue to show details in Venus's clouds. (NASA/JPL)
The second planet from the Sun is a pressure cooker.
Radar sees through the planet's thick cloud.
The Magellan spacecraft ended its mission in 1994 after mapping the surface of Venus using cloud penetrating radar. The probe revealed numerous volcanoes and lava flows around the planet. Venus's noxious atmosphere, high temperatures and pressures make landing a probe on the surface very difficult.
Sir Patrick Moore talks about Pioneer 13's mission.
Sir Patrick Moore describes the Pioneer 13 probe's findings in a 1982 edition of the Sky at Night. He talks about volcanism on the planet and the hostile conditions at the surface. Though Sir Patrick speaks about active volcanism on Venus, a volcanic eruption has not been witnessed there.
Sir Patrick Moore and his guest explain the Magellan probe's instruments.
Sir Patrick Moore and his guest Dr Peter Cattermole discuss Magellan's radar and other instruments as the probe starts its mapping mission at Venus in 1990.
Sir Patrick Moore talks about the first Venera images taken from Venus's surface.
In 1975 the Soviet Venera 9 and 10 missions managed to survive the punishing conditions on Venus long enough to return photographs of the rocky world. Sir Patrick talks to Dr Garry Hunt about the probes and the images they returned.
Sir Patrick Moore and Dr Peter Cattermole discuss the probe's first images of Venus.
Sir Patrick Moore and his guest Dr Peter Cattermole have a look at the first radar images of Venus returned from the Magellan probe in 1990. Dr Cattermole describes and interprets the geology of Venus on the basis of what he sees in the images.
Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. It has no natural satellite. It is named after the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6, bright enough to cast shadows. Because Venus is an inferior planet from Earth, it never appears to venture far from the Sun: its elongation reaches a maximum of 47.8°.
Venus is a terrestrial planet and is sometimes called Earth's "sister planet" because of their similar size, mass, proximity to the Sun and bulk composition. It is radically different from Earth in other respects. It has the densest atmosphere of the four terrestrial planets, consisting of more than 96% carbon dioxide. The atmospheric pressure at the planet's surface is 92 times that of Earth's. With a mean surface temperature of 735 K (462 °C; 863 °F), Venus is by far the hottest planet in the Solar System, even though Mercury is closer to the Sun. Venus has no carbon cycle that puts carbon into rock, nor does it seem to have any organic life to absorb carbon in biomass. Venus is shrouded by an opaque layer of highly reflective clouds of sulfuric acid, preventing its surface from being seen from space in visible light. It may have possessed oceans in the past, but these would have vaporized as the temperature rose due to a runaway greenhouse effect. The water has most probably photodissociated, and, because of the lack of a planetary magnetic field, the free hydrogen has been swept into interplanetary space by the solar wind. Venus' surface is a dry desertscape interspersed with slab-like rocks and periodically refreshed by volcanism.