Venus

(TFS) - Venus is the planet that most closely resembles the Earth by its size, but its atmosphere is mainly composed of carbon dioxide.

It 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%.

Planet Profile

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

Diameter: 12,103.6 km

Mass: 4.869e24 kg

Also known as the Shepherd's Star, Venus is located at 108 kiolmeters from the sun. It is surrounded by a thick layer of clouds. Venus is a real furnace: its surface temperature is 460 ° C. This heat is due to the activity of numerous volcanoes which project into the atmosphere of the gases, and act like the windows of garden’s a greenhouse under the effect of the sun, leading to the elevation of the temperature on the ground. Under these inhospitable conditions, water is not present on Venus.

Although this planet resembles to the earth. It is almost as large and was created from the same mass of gas and rocks. Its temperature has not always been as high. According to scientists, water in the form of ice, liquid or steam existed since the time of its creation. But since it was closer to the Sun than the earth, it received more heat, and the water evaporated.

Spacecrafts

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. The first orbiter, the US spacecraft Magellan  radar map produced detailed maps of Venus' surface using radar. ESA's Venus Express launched in November of 2005 and arrived at Venus in April 2006. The Venus Express is conducting atmospheric studies, mapping the Venusian surface temperatures and the plasma environment.

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.

Similarities with Earth

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.

 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 sulphuric 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 has a vortex at each pole. These vortices rotate vertically and recycle the atmosphere downwards. The north polar vortex has a peculliar double eye shape surrounded by a collar of cool air; it makes a complete rotation in three Earth days.

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.

Winds on Venus

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.

Data from Magellan's imaging radar shows that much of the surface of Venus is covered by lava flows. There are several large shield volcanoes (similar to Hawaii or Olympus Mons) such as Sif Mons. Recently announced findings indicate that Venus is still volcanically active, but only in a few hot spots; for the most part it has been geologically rather quiet for the past few hundred million years.

Volcano and Lava Flows on Venus

There are no small craters on Venus. It seems that small meteoroids burn up in Venus' dense atmosphere before reaching the surface. Craters on Venus seem to come in bunches indicating that large meteoroids that do reach the surface usually break up in the atmosphere.

The oldest terrains on Venus seem to be about 800 million years old. Extensive volcanism at that time wiped out the earlier surface including any large craters from early in Venus' history.

 Venusian coronae Venusian pancakes Magellan's images show a wide variety of interesting and unique features including pancake volcanoes (left) which seem to be eruptions of very thick lava and coronae (right) which seem to be collapsed domes over large magma chambers.

Pancake Volcanoes on Venus

Venus has no magnetic field, perhaps because of its slow rotation.
Venus has no satellites, and thereby hangs a tale.

Venus is usually visible with the unaided eye. Sometimes (inaccurately) referred to as the "morning star" or the "evening star", it is by far the brightest "star" in the sky. There are several Web sites that show the current position of Venus (and the other planets) in the sky.

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Source: http://nineplanets.org/venus.html