Venus is the Roman goddess of love and so it is appropriate that she shares her name with the hottest planet in the Solar System. The average surface temperature of the planet is 735° Kelvin or 460° Celsius; in contrast, the average surface temperature of Mercury, which is 50% closer to the sun, is 420° C. There are also no variations in temperature no matter where on the planet you are and whether it is day or night. However, if you can get up to 50 km to 65 km above the surface, the atmosphere and temperature become increasingly Earth-like.
The reason Venus is so hot and has no temperature variations is its atmosphere. The atmosphere of the planet is nearly 96% carbon dioxide and 4% nitrogen, as well as being 90 times denser than that of Earth, resulting in a runaway greenhouse effect in which energy from the Sun is trapped on the surface of the planet. A contributory factor is the Venus’s very slight axial tilt, just 2.7° compared with Earth’s 23.4°, meaning that it receives the same amount of energy from the Sun no matter what time of year it is. The atmosphere is also covered in clouds made up of sulfuric acid and other corrosive substances, as well as having powerful winds with speeds reaching over 100 meters per second.
However, Venus was not always this hot. Many scientists even believe that at one time, Venus was like Earth, with liquid oceans and plate tectonics. But it is unclear why the runaway greenhouse effect happened on Venus. One theory is that the brightness of the early Sun caused an increase of water vapor in the atmosphere, causing an increase in temperature and the oceans to eventually boil until all its water vapor entered the atmosphere. The weak carbon recycling cycle on Venus may also have contributed to carbon dioxide becoming the dominant gas in the atmosphere.
Additional Facts about Venus