Venus

Venus is often called Earth’s “sister” or “twin” planet because it’s similar to our home in size, mass and composition, but that’s about it. A closer look at Venus reveals uninhabitable wasteland, covered with volcanoes and its atmosphere, made mostly of carbon dioxide, is so thick, the pressure at surface is crushing. Add the hottest-of-all-planets surface temperature of 462 degrees Celsius and you get the picture why Venus is anything but Earth’s twin.

Planet Venus. Credit: ESA/MPS/DLR/IDA, M. Pérez-Ayúcar & C. Wilson

After the Moon, Venus is the brightest object in the night sky, known to humans since ancient times, but since it’s closer to the Sun than Earth, from our perspective it never wanders far away from the bright star. This means that we can only see Venus a few hours after the sunset and before the sunrise. For this reason, in ancient times it was known as both “Morning Star” and “Evening Star” and was often thought to be two different stars.

Planet named after Roman goddess of love and beauty orbits the Sun at about 108 million kilometres or 0.72 astronomical units (AUs, distance between Earth and the Sun). When closest to us, it is only 41 million kilometres away. It takes Venus 224.6 days to complete a full orbit and it does so on a path that is almost circular. All planets orbit our star along elliptical orbits, but Venus’s orbital eccentricity is less than 0.01 i.e. almost perfect circle.

Venus by Hubble space telescope

Except Uranus, Venus is the only planet with retrograde rotation around its axis i.e. while it orbits the Sun counterclockwise, it rotates around its axis in clockwise direction. Unlike Uranus which was tipped over by an impact with another body during the formation of the planets, Venus’s rotation was actually reversed after a similar impact. Although technically planet’s axial tilt is designated to be 177.4 degrees because of the retrograde rotation, it is in effect less than 3 degrees (180 degrees minus 177.4 degrees). Check Uranus information page if you want to know logic behind this. Small axial tilt means there are no seasons on Venus as we on Earth know them.

Nowadays, Venus rotates very slowly around its axis - once every 243 Earth days. Yes, it takes longer for the planet to rotate around its own axis than orbit the Sun! However, if you stood on the Venus’s surface and somehow managed to survive the pressure and see the Sun from the thick atmosphere, you’d experience the Venusian day to be “only” 116.75 Earth days long. The reason lies in planet’s retrograde rotation. You’d also notice the Sun rising in the west and setting in the east.

Planet Venus transiting in front of the SunPlanet Venus transiting in front of the Sun

Venus is 12,092 kilometres in diameter, only 650 km less than Earth. Because it rotates slowly, it is highly spherical, so its pole to pole diameter and diameter at equator are almost the same. It is one of four rocky planets and since its similar in size and density to Earth, its internal structure is probably similar, consisting of partially liquid core, mantle and crust without plate tectonics. As already mentioned, Venusian atmosphere is very thick, made of 96.5% carbon dioxide and 3% nitrogen. It possibly had oceans in the past, but with greenhouse effect caused by so much carbon dioxide in the atmosphere, they boiled away long time ago. Sulfur dioxide and sulfuric acid in the atmosphere, produced by Venusian many volcanoes, reflect 90% of sunlight back into space. Unlike the planet itself, winds on Venus circle the planet every four to five Earth days, about 60 times faster than planet’s rotation, reaching speeds up to 300 km/h.

Computer simulation of planet Venus's surfaceComputer simulation of planet Venus's surface

Because most of the sunlight is reflected back into space, Venus has a dark surface, shaped by many volcanoes, over 160 of them more than 100 km across. About 80% of planet’s surface is covered by volcanic plains.

Venusian volcano cratersVenusian volcano craters

Being so close to Earth, Venus was intensively observed since ancient times, but with 1960s and start of Russian Venera and USA’s Mariner programs, came better data about Venusian atmosphere and surface. Venera 9 probe sent first picture from the surface of Venus on October 22, 1975.

Images of Venusian surface taken by Venera 14Images of Venusian surface taken by Venera 14

All images credited to NASA, except where otherwise noted

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