Venus

1. Characteristics

Venus is the second closest planet to the Sun. It takes about 225 days to orbit the Sun, and almost 2 days pass on Venus during this time[1]. Apart from the Sun and Moon, Venus is the brightest natural object in space that is visible from Earth. Venus is never far from the Sun and so, like Mercury, is best observed in the early morning or at twilight. The name Venus is also Roman in origin, referring to the goddess of love and beauty[2a].

Photograph of Venus above the clouds.

Ultraviolet image of Venus, taken using the Pioneer Venus Orbiter. Image credit: NASA/Public domain.

Photograph of Venus taken below the clouds.

Venus below the clouds, using data from Magellan. Image credit: NASA/JPL/Public domain.

Venus is sometimes called Earth's 'sister planet' because it's a similar size, mass, and density to the Earth[3]. Venus may have once contained large oceans but it has undergone an extreme greenhouse effect and the water has evaporated, leaving a dry, desert landscape[4].

Venus is now covered in a thick atmosphere of carbon dioxide, with sulfuric acid clouds. The atmospheric pressure on Venus is almost 100 times that of Earth's, and the atmosphere reflects sunlight back into space before it can reach the planet's surface. Venus is covered in volcanoes but there are relatively few craters, indicating that its surface must be fairly new, at about half a billion years old[2b].

Planets in the Solar system, sizes are approximately to scale. Jupiter is the largest planet, followed by Saturn.

The planets, sizes approximately to scale. Image credit: Dave Jarvis/CC-SA.

The four inner planets, Mercury, Venus, Earth, and Mars, and the Moon. Sizes are approximately to scale, and the composition is shown.

The four inner planets to scale. Image credit: NASA/Public domain.

2. Missions to Venus

Venus is the closest planet to the Earth, and over 40 attempts have been made to send probes to Venus, beginning in 1961, when the Soviet Union launched Sputnik 7. This would have been the first space probe to be sent to another planet, but it failed before it left low Earth orbit. Later that year, the Soviet's Venera 1 became the first probe to be sent to another planet, although they lost contact with it before it arrived at Venus.

NASA launched their first probe to Venus, Mariner 1, in 1962. This was lost too, but Mariner 2 completed its mission later that year, passing about 35,000 km from the surface of Venus.

The Soviet Union also attempted to send multiple probes to Venus in 1962 - Sputnik 19, Sputnik 20, and Sputnik 21 - but they all failed to escape the Earth's orbit. They attempted 10 more failed missions between 1963 and 1967, including Venera 3, which was launched in 1965, and crash-landed on Venus in 1966, becoming the first human-made object to strike the surface of another planet.

The Soviet's first successful mission to Venus occurred in 1967, with Venera 4, which became the first human-made device to successfully land on another planet, and the first to successfully transmit data back to Earth.NASA's Mariner 5 flew past Venus the day after Venera 4 landed, and data from the Soviet and American missions were shared.

The Soviet Union completed 12 more successful Venera missions, Venera 5 - Venera 16, between 1969 and 1983. They also launched two unsuccessful Cosmos missions to Venus, with Cosmos 359 in 1970, and Cosmos 482 in 1972. Finally, they had two more successes in 1985, with Vega 1 and Vega 2, which went on to fly past Halley's Comet.

NASA's Mariner 10 successfully flew past Venus in 1974, on its way to Mercury. NASA's Pioneer 1, the Pioneer Venus Orbiter, and Pioneer 2, the Pioneer Venus Multiprobe, were launched in 1978, and reached Venus later that year. The Pioneer Venus Multiprobe released four probes into the atmosphere, and the Pioneer Venus Orbiter went into orbit and then used radar to map the surface. It transmitted data back to Earth until 1992. The remainder of Venus was mapped by NASA's Magellan spacecraft, which was launched in 1989, and reached Venus in 1990, where it remained in orbit until 1994.

NASA's Galileo spacecraft flew past Venus in 1990, before travelling to Jupiter, and the Cassini spacecraft flew past Venus in 1998 and 1999, before travelling to Saturn. The Cassini mission was a joint project between NASA, the ESA, and the Italian Space Agency.

The ESA launched their own Venus orbiter in 2005, the Venus Express, and this remained in orbit around Venus from 2006 until 2015. JAXA launched three probes to Venus in 2010, Akatsuki (PLANET-C), IKAROS, and Shin'en (UNITEC-1). Akatsuki and Shin'en failed, but IKAROS successfully flew past Venus, using solar sail technology. JAXA remained in contact with Akatsuki, and it made a second attempt to fly past Venus in March 2016. This time it was successful.

The BepiColombo mission to Mercury aims to fly past Venus in 2019 and 2020. The ISRO (Indian Space Research Organisation) may launch the Indian Venusian orbiter by 2020 in order to study the atmosphere of Venus. NASA may launch an orbiter - VERITAS - and a probe - DAVINCI - to Venus as part of the Discovery program in 2021, and the Russian Federal Space Agency is due to launch a probe to Venus, Venera-D, in 2024.

3. References

  1. NASA, 'Planetary Fact Sheet', last accessed 15-02-16.

  2. (a, b) NASA, 'Venus: In Depth', last accessed 15-02-16.

  3. NASA, 'Why We Explore: Voyages to the Planets: Venus', last accessed 15-02-16.

  4. NASA, 'Why Venus?', last accessed 15-02-16.

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