Venus

Venus is the second planet from the Sun and the sixth largest. Venus' orbit is the most nearly circular of that of any planet, with an eccentricity of less than 1%.

orbit: 108,200,000 km (0.72 AU) from Sun

diameter: 12,103.6 km

mass: 4.869e24 kg

Hardcopy

The New Solar System

Summarizes what we havve learned from interplanetary explorations in the last 25 years. My primary reference for The Nine Planets.

Venus Revealed

The latest results from Magellan in an accessible and easygoing book. Covers mythology and history of our "sister planet" as well as up to date science and a history of the Magellan project.

Venus in Transit

Fascinating account of past transits and the woes that befell those involved.

Venus (Greek: Aphrodite; Babylonian: Ishtar) is the goddess of love and beauty. The planet is so named probably because it is the brightest of the planets known to the ancients. (With a few exceptions, the surface features on Venus are named for female figures.)

Venus has been known since prehistoric times. It is the brightest object in the sky except for the Sun and the Moon. Like Mercury, it was popularly thought to be two separate bodies: Eosphorus as the morning star and Hesperus as the evening star, but the Greek astronomers knew better. (Venus's apparition as the morning star is also sometimes called Lucifer.)

Since Venus is an inferior planet, it shows phases when viewed with a telescope from the perspective of Earth. Galileo's observation of this phenomenon was important evidence in favor of Copernicus's heliocentric theory of the solar system.

Venera 9 surface photo The first spacecraft to visit Venus was Mariner 2 in 1962. It was subsequently visited by many others (more than 20 in all so far), including Pioneer Venus and the Soviet Venera 7 the first spacecraft to land on another planet, and Venera 9 which returned the first photographs of the surface. Most recently, the orbiting US spacecraft Magellan Magellan radar map (false color) produced detailed maps of Venus' surface using radar.

Venus' rotation is somewhat unusual in that it is both very slow (243 Earth days per Venus day, slightly longer than Venus' year) and retrograde. In addition, the periods of Venus' rotation and of its orbit are synchronized such that it always presents the same face toward Earth when the two planets are at their closest approach. Whether this is a resonance effect or merely a coincidence is not known.

Venus is sometimes regarded as Earth's sister planet. In some ways they are very similar:

* Venus is only slightly smaller than Earth (95% of Earth's diameter, 80% of Earth's mass).

* Both have few craters indicating relatively young surfaces.

* Their densities and chemical compositions are similar.

Because of these similarities, it was thought that below its dense clouds Venus might be very Earthlike and might even have life. But, unfortunately, more detailed study of Venus reveals that in many important ways it is radically different from Earth. It may be the least hospitable place for life in the solar system.

Venus in visible light from Galileo The pressure of Venus' atmosphere at the surface is 90 atmospheres (about the same as the pressure at a depth of 1 km in Earth's oceans). It is composed mostly of carbon dioxide. There are several layers of clouds many kilometers thick composed of sulfuric acid. These clouds completely obscure our view of the surface. This dense atmosphere produces a run-away greenhouse effect that raises Venus' surface temperature by about 400 degrees to over 740 K (hot enough to melt lead). Venus' surface is actually hotter than Mercury's despite being nearly twice as far from the Sun.

Venus in ultra-violet light There are strong (350 kph) winds at the cloud tops but winds at the surface are very slow, no more than a few kilometers per hour.

Venus probably once had large amounts of water like Earth but it all boiled away. Venus is now quite dry. Earth would have suffered the same fate had it been just a little closer to the Sun. We may learn a lot about Earth by learning why the basically similar Venus turned out so differently.

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