Venus (planet)

Venus Orbital characteristics Avg Dist from Sol 0.72333199 AU Mean radius 108,208,930 km Eccentricity 0.00677323 Revolution period 224.701 days Synodic period 583.92 days Avg. Orbital Speed 35.0214 km/s Inclination 3.39471° Number of satellitess 0 Physical characteristics Equatorial diameter 12,103.6 km Surface area 4.60×108 km2 Mass 4.869×1024 kg Mean density 5.24 g/cm3 Surface gravity 8.87 m/s2 Rotation period -243243.0187 days Axial tilt 2.64° Albedo 0.65 Escape Speed 10.36 km/s Surface* temp min* mean max 228 K 737 K 773 K (*min temperature refers to cloud tops only)
Atmospheric characteristics
Atmospheric pressure	9321.9 kPa
Carbon dioxide	96%
Nitrogen	3%
Sulfur dioxide Water vapor Carbon monoxide Argon Helium Neon Carbonyl sulfide Hydrogen chloride Hydrogen fluoride	trace

Venus is the second planet from the Sun, named after the Roman goddess Venus. It is a terrestrial planet, very similar in size and bulk composition to Earth; it is sometimes called Earth's "sister planet" as a result of this similarity. Sometimes (inaccurately) referred to as the "morning star" or the "evening star", it is by far the brightest "star" in the sky. Because Venus is closer to the Sun than Earth is, it is always in roughly the same direction as the Sun, so can only be seen just before sunrise or just after sunset.

Physical characteristics

Atmosphere

Venus has an atmosphere consisting mainly of carbon dioxide and a small amount of nitrogen, with a pressure at the surface about 90 times that of Earth (a pressure equivalent to a depth of 1 kilometer under Earth's ocean). This enormous CO₂-rich atmosphere results in a strong greenhouse effect that raises the surface temperature approximately 400°C above what it would be otherwise, causing temperatures at the surface to reach 500°C. This makes Venus's surface hotter than Mercury's, despite being nearly twice as distant from the Sun and only receiving 75% the solar irradiance (2660 W/m²). Due to the thermal inertia and convection of its dense atmosphere, the temperature does not vary significantly between the night and day sides of Venus despite its extremely slow rotation (less than one rotation per Venusian year). Winds in the upper atmosphere circle the planet in only 4 days, helping to distribute the heat.

There are strong 350-kilometer-per-hour winds at the cloud tops but winds at the surface are very slow, no more than a few kilometers per hour. However, due to the high density of the atmosphere at Venus's surface, even such slow winds exert a significant amount of force against obstructions. The clouds are composed of sulfur dioxide and sulphuric acid droplets and cover the planet completely, obscuring any surface details. The temperature at the tops of these clouds is approximately -45°C. The official mean surface temperature of Venus, as given by NASA, is 464°C. The minimal value of the temperature, listed in the table, refers to cloud tops - on surface the temperature is never below 400°C.

Surface features

Venus has slow retrograde rotation, meaning it rotates from east to west instead of west to east as all other known planets in the solar system do. It is not known for sure why Venus is different in this manner, although it may be the result of a collision with a very large asteroid at some time in the distant past. In addition to this unusual retrograde rotation, the periods of Venus's rotation and of its orbit are synchronized in such a way that it always presents the same face toward Earth when the two planets are at their closest approach (5.001 Venusian days between each inferior conjunction). This may be the result of tidal locking, with tidal forces affecting Venus's rotation whenever the planets get close enough together, or it may simply be a coincidence.

Venus has two major continent-like highlands on its surface, rising over vast plains. The northern highland is named Ishtar Terra and has Venus's highest mountains, named the Maxwell Montes after James Clerk Maxwell, which surround the plateau Lakshmi Planum. Ishtar Terra is about the size of Australia. In the southern hemisphere is the larger Aphrodite Terra, about the size of South America. Between these highlands are a number of broad depressions, including Atalanta Planitia, Guinevere Planitia, and Lavinia Planitia. With only the exception of Maxwell Montes, all surface features on Venus are named after real or mythological females. Due to Venus's thick atmosphere, which causes meteors to decelerate as they fall toward the surface, no impact crater smaller than about 3.2 km in diameter can form.

Nearly 90% of Venus's surface appears to consist of recently-solidified basalt lava, with very few meteor craters. This suggests that Venus underwent a major resurfacing event recently. The interior of Venus is probably very similar to that of Earth: an iron core about 3000 km in radius, with a molten rocky mantle making up the majority of the planet.