Meet our neighbours: Venus

Venus is the second-closest planet to the Sun, with a mean distance of 108 million km. It takes 225 days to revolve around the Sun. With a diameter of 12,100 km, it has a size very similar to that of the Earth.

Venus, the "morning star"
Like Mercury, Venus never appears very far from the sun in the sky, either as a bright “morning star” or “evening star”. When observed with a telescope, the disk of Venus shows “phases”, just as the Earth’s Moon does to the naked eye, appearing as a crescent, a half-circle, or a fuller circle. As early as 1610, the Italian astronomer Galileo used his observations of the phases of Venus to argue that the planets revolve around the sun, which is at the centre of the solar system.

Like Mercury, Venus transits in front of the sun on rare occasions. The last transits occurred on June 8, 2004, and June 6, 2012, but the next ones will occur in 2117 and 2155. During the 18th and 19th centuries, astronomers used these transits to accurately measure the distance from the Earth to the Sun. Since the scale of the whole solar system was based on that distance, this gave humans the first clear idea of the size of their celestial environment.

Venus' atmosphere and clouds
Venus has a thick atmosphere mainly composed of CO2 (96%) and N2 (3,5%), with traces of SO2, argon and water vapour. The surface pressure is 90 times the atmospheric pressure on Earth and the temperature reach 465°C on average. These extreme conditions are caused by an intense greenhouse effect that developed in the early stages of the planet’s climatic evolution and led to the loss of almost all of the initial water content of the atmosphere.
Today, Venus has a runaway greenhouse effect due to this dense carbon dioxide atmosphere, which traps heat and causes extremely high surface temperatures. This effect is far more intense than on Earth, making Venus inhospitable. The thick atmosphere and cloud layers on Venus trap infrared radiation, leading to a significant increase in surface temperature. For this reason surface temperature of Venus is extremely hot, averaging around 500°C.
The surface of Venus is also permanently veiled by a thick layer of clouds partly composed of sulphuric acid (materialized by the layer of fabric covering the tactile image). These clouds rotate around the planet in about four days, as they are blown by winds with speeds reaching 550 km/h at the equator.

Volcanoes and lava channels
Despite the thick cloud layers, it was possible to “image” the surface of Venus using radar onboard NASA’s probe Magellan that orbited the planet between 1989 and 1994. The image you are using is based on the map established with this technique. Magellan revealed a landscape shaped by ancient volcanic activity, with regions of high plateaus towering 3 to 5 km above vast basaltic plains that occupy about 80% of the surface. These plateaus are traversed by lava channels hundreds of kilometres long (materialized by clumps of soft fabric on the tactile image), originating from many volcanoes (materialized by buttons on the tactile image). More than 1,000 volcanoes or volcanic centres larger than 20 km in diameter dot the surface of Venus. There may be close to a million volcanic centres that are over 1 km in diameter. Many other geological formations are the result of intense volcanic activity in a distant past.