Venus
What is Venus?
Planets· Diameter 12,104 km. Nearly Earth's twin in size and mass, Venus is the hottest planet, because a thick carbon dioxide atmosphere traps heat and keeps the surface at 464 °C. After the Sun and Moon it is the brightest object in our sky, seen as the morning and evening star.
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Orbit and size
| Diameter | 12,104 km |
|---|---|
| Distance | 0.72 AU |
| Year | 225 d |
| Temp | 464 °C |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Related events
Fifty kilometres above Venus, the most Earth-like air
Down on the ground Venus is all heat and crushing air, but conditions change with height. Between 50 and 60 km up, above the main cloud deck, the pressure is close to Earth's at sea level and the temperature lies between 0 and 50 °C. Since the 1970s this has inspired ideas for floating balloons or even stations there. In 1985 two balloons dropped by the Soviet Vega probes actually drifted at that height for nearly two days, carried more than 10,000 km by the wind.
Floating at that height is easier than it sounds. The carbon dioxide in Venus's atmosphere is heavier than Earth's air, so a balloon filled with ordinary breathable air, nitrogen and oxygen, rises there the way a helium balloon rises here. The hard part is that the clouds are sulfuric acid, so equipment has to be protected from corrosion.
Venus was also the first other planet a spacecraft landed on. In 1970 the Soviet Venera 7 sent signals from the surface for 23 minutes, and in 1982 Venera 13 returned colour pictures and lasted 127 minutes. Because of the heat and pressure, no lander has survived longer. In the 1990s NASA's Magellan used radar to map 98 percent of the surface beneath the clouds.
The planet in depth
Venus is almost the same size and mass as Earth, which is why it is called Earth's twin. Its surface, though, could hardly be more different. The air is mostly carbon dioxide and presses down about 90 times harder than Earth's, similar to the pressure 900 m deep in our oceans. The clouds are made not of water but of droplets of sulfuric acid.
Venus is hot because of the greenhouse effect. Carbon dioxide traps the Sun's heat like a blanket, holding the surface at 464 °C day and night, hot enough to melt lead. Venus is almost twice as far from the Sun as Mercury, yet this blanket makes it hotter. Scientists think Venus once had water too, but being a little closer to the Sun than Earth, it lost that water to evaporation, and the vapor made the greenhouse even stronger.
Its spin is odd as well. One turn takes 243 days, longer than its 225-day trip around the Sun, and it turns the opposite way from most planets. So on Venus the Sun rises in the west and sets in the east, and daylight lasts about 58 Earth days. Why Venus spins backward is still unknown.
In Earth's sky Venus is the brightest object after the Sun and Moon. At its brightest it reaches magnitude −4.6, enough to cast faint shadows in a very dark place. In 1610 Galileo saw through his telescope that Venus shows phases like the Moon. This was evidence that Venus goes around the Sun, not around Earth.
Frequently asked
- How big is Venus?
- The diameter of Venus is 12,104 km.
- How far is Venus from Earth?
- The distance of Venus is 0.72 AU.
- In one line, what is Venus?
- Planets — Nearly Earth's twin in size and mass, Venus is the hottest planet, because a thick carbon dioxide atmosphere traps heat and keeps the surface at 464 °C.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.