Period of rotation (equatorial): 243.0 days (retrograde)
Mean orbital velocity: 21.8 miles (35 km) per second
Inclination of axis: 178 í
Orbital eccentricity: 0.007
Orbital inclination: 3.39 í
Diameter at equator: 7,523 miles (12,104 km)
0.949 x Earth's diameter
Oblateness: 0
Mass: 4.87 x 10^24 kg
0.815 x Earth's mass
Volume: 9.32 x 10^11 km^3
0.86 x Earth's volume
Density: 5.24 g/cm^3
0.949 x Earth's density
Surface gravity: 8.60 m/s^2
0.90 x Earth's gravity
Escape velocity: 6.4 miles (10.4 km) per second
Mean surface temperature: 896 F / 480 C / 753 K
Maximum apparent diameter as seen from Earth: 65.2╙
Albedo: 0.76
Number of known moons: 0
Mean diameter of Sun as seen from the planet: 44' 15"
Planet composition
Researchers believe that Venus, which is almost perfectly spherical, has a liquid iron core smaller than the Earth's. This would be surrounded by a mantle composed of silicates. However, it is possible that Venus does not have a discrete core, and has iron and silicates mixed throughout the planet instead of being separated into a mantle and core.
The crust ranges from 25 km thick in the lowlands to 160 km thick in the highlands. This relatively thick static crust may be composed of a single plate. Soil samples taken by Veneras 9 and 10 indicate that Venus' crust has a composition similar to terrestrial ocean deposits.
Core: radius of 2800 to 3100 km
Mantle: 3000 km thick
Crust: 25 to 160 km thick
Topography
The topography of Venus is diverse. A series of large (up to 150 km in diameter) but shallow craters populate the surface. There are also highlands (average elevation of 3 km) and a system of faults. The two large highlands areas are Ishtar Terra, in the northern hemisphere, and Aphrodite Terra, slightly to the south of the equator. Ishtar Terra is about the size of Australia, and its highest point (11 km) occurs in a grouping known as the Maxwell Mountains. Aphrodite Terra is about the size of Africa and its highest point is 7 km. Diana Chasma is Venus' largest valley, lying about 4 km below the surrounding ridges. The largest basin is Atlanta Planitia, which is comparable in size to the Gulf of Mexico.
Atmosphere
The atmosphere of Venus is composed primarily of carbon dioxide (96%). The rest is mostly nitrogen, with sulfuric acid, carbon monoxide, oxygen, water vapor, hydrochloric acid, and hydrofluoric acid all present in trace amounts. Venus' atmosphere is so dense that the pressure at the surface is over 90 times greater than on the surface of the Earth. Only at an elevation of 50 km does the pressure reach the Earth's sea-level pressure.
The majority of Venusian clouds consist of sulfuric acid droplets which condense at altitudes between 45 and 75 km. They form broad bands in the atmosphere, and their thickness hides the surface of the planet from view.
The large amount of carbon dioxide causes an effect known as greenhouse warming: solar energy which is reflected from the Venusian surface is absorbed by the carbon dioxide as well as sulfuric acid. Therefore, heat is trapped within the atmosphere and is distributed across the planet, making the surface extremely hot (896 F / 480 C / 753 K).
Magnetic fields and gravity
Though Venus has only a very small magnetic field, it still interacts with the solar wind. An ionosphere is created in Venus' thick atmosphere as high energy solar wind particles collide with and ionize neutral atmospheric atoms and molecules. The ionosphere causes a bow shock on the side of Venus facing the Sun; away from the Sun it extends outwards in a tear-shaped tail. There are many charged particles which constitute the ionosphere, but none of them are magnetically trapped in radiation belts.
The gravity at the surface of Venus is 0.902 times the Earth's gravity.
Orbit and rotation
Venus has the most circular orbit of any planet. Its rotation is also unique: First, it takes longer for the planet to rotate on its axis than it takes to orbit the Sun. (The globe rotation is at the equator is 243 days, whereas the planet's year is only 224.7 days.) Second, Venus rotates east to west, which is retrograde (backward) from that of the Sun and most other planets. Finally, it's interesting to note that Venus' upper atmosphere rotates around the planet in only four days, while the planet itself takes 243 days to complete one revolution.
Moons and/or rings
Venus is so bright it sometimes produces a ghost image. Astronomers in the 17th and 18th centuries thought the image to be a satellite, but it has since been confirmed that there are no satellites associated with Venus.
Mythology
Venus has been known for centuries. The ancient Babylonians named it Nin-dar-Anna, "Mistress of the Heavens;" the Chinese, Tai-pe, "The Beautiful White One;" the Greeks, Hesperus, the "Evening star," and Phosphorus, the "Morning star."
The planet is named for the Roman goddess of love and beauty, and astrologers believed that any child born under the rays of Venus would be blessed with those features. Venus was the symbol of gentleness and charm, a taste for music, harmony, playfulness, and generosity. Friday, in ancient times, was dedicated to Venus.
Discovery and exploration
Galileo first viewed Venus close-up using an "optick tube" in 1610. In the eighteenth century, J.H. Schroeter confirmed the existence of an atmosphere.
In the nineteenth century, imaginative speculation regarding possible life forms on Venus abounded, fueled by the fictional writings of Jules Verne. Illustrations of Venusian creatures appeared in many popular magazines of the day. No life, however, has ever been found on the planet.
Because of the atmosphere, direct photography of Venus' surface is impossible. The only method of exploring the planet from Earth is by using radar. In recent years, the US and former USSR have sent many missions to explore Venus, including:
The Mariner missions, begun in December 1962 by the US.
The Venera missions, begun in February 1966 by the USSR.
