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.
In 1962 some thought Venusian life was possible.
Prior to Mariner 2's 1962 flyby of Venus, some scientists such as Dr Carl Sagan thought that conditions on the planet might favour life. However, the probe's instruments showed that the cloudy planet's surface was extremely hot, greatly reducing the chance that anything could survive there.
The Russians try to reveal cloudy Venus's secrets.
The Russian Venus probe Venera 4 arrived at the planet in October 1967. As it entered the thick Venusian atmosphere, unexpectedly high pressures destroyed the craft as it descended. However, the probe managed return data to the Earth.
Can the Russians design a spacecraft capable of surviving Venus's extreme pressures?
The Russians took on the challenge of building a probe strong enough to survive the incredibly high atmospheric pressures on Venus. Ultimately they succeeded with Venera 7 in 1970. The subsequent Venera 9 mission returned photographs of the planet's volcanic surface.
The inner planets' atmospheres developed very differently.
Researchers believe that in the early days of the Solar System, Earth, Venus and Mars had similar atmospheres, but they developed very differently. Mars couldn't hold onto its atmosphere, while a runaway greenhouse effect may have boiled away oceans on Venus. Earth, on the other hand, benefited from its greenhouse effect.
The orbiting probe maps the planet's surface with radar and finds many strange sights.
After arriving at the planet in 1989, the Magellan probe orbited Venus many times and used its radar to map the cloud-covered surface. The data revealed a surface with numerous volcanoes and geological features unlike any seen on the Earth.
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, gravity, and bulk composition (Venus is both the closest planet to Earth and the planet closest in size to Earth). However, it has also been shown to be very 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. It has no carbon cycle to lock carbon back into rocks and surface features, nor does it seem to have any organic life to absorb it 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. Venus 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's surface is a dry desertscape interspersed with slab-like rocks and periodically refreshed by volcanism.