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Venus

The planet Venus, is the brightest object after the Sun and the Moon. It is the second planet from the Sun, sometimes called twin sister planet of the Earth, and the closest planet to the Earth as it can reach us to a distance of 0.27 AU. Venus is the brightest of the celestial objects, after the Sun and the Moon. It can have a maximum magnitude up to ?4.6. As Venus is an inferior planet its elongation reaches a maximum of 47.8° from the Sun and many nations it is called the Morning Star or Evening Star as it always appears before sunrise or after sunset.

Venus rotates counterclockwise, completing a full orbit around the Sun in 224.7 days, almost equal to 1.92 Venusian solar days (rotations of the planet with respect to the Sun). Venus is rocky, with an extremely dense atmosphere that prevents us from observing its surface. The NASA spacecraft “Magellan”, using radar that penetrated into the atmosphere, provided us with detailed maps the surface. It was revealed that Venus is covered by volcanoes and as well as the presence of relatively recent lava. The  latter indicates that the planet is probably geologically active. There are 1,600 major volcanoes and also lots of gorges and craters.

Venus has a totally different geology than the Earth and higher temperature and denser atmosphere with a surface temperature up to 736 K, while the surface pressure is ninety times that of Earth. The planet has practically no water; as if all water was concentrated it could create a water cover of 2 cm. In the Venusian atmosphere dominate thick clouds of ~96.5% carbon dioxide, ~3.5% nitrogen, 0.015% sulfur dioxide and traces of argon, water vapors, carbon monoxide, helium, neon, carbonyl sulfide, hydrogen chloride, hydrogen fluoride.

The extremely densed atmosphere of Venus is enriched with carbon dioxide which is a very effective greenhouse gas and increases the temperature of a planet that has it in its atmosphere. Carbon dioxide allows the penetration of sunlight but absorbs the infrared radiation that is emitted by the planet at low wavelengths as it has a temperature lower than the Sun. As Venus becomes hotter emits more carbon dioxide and enhances the Greenhouse effect. This effect is called “Uncontrollable Greenhouse Effect”. It is believed that Venus was initially more Earth like and that it changed drastically due to the Greenhouse effect.

An intrinsic magnetic field would have been expected via the dynamo mechanism, if Venus had a faster rotation, since the core of Venus has similar dimensions to the Earth one and probably consists of liquid iron and nickel. However, Venus has only a weak magnetic field. The planet is protected against the solar wind via a dense ionosphere. The interaction of the ionosphere with the solar wind induces the weak magnetic field measured in Venus producing a magnetosphere similar to the one of comets and to an extend Mars.

The water of the atmosphere of Venus has much more deuterium than the Earth and this indicates that a lot of water, an ocean, has been replenished in the past due to the interaction of the atmosphere with the solar wind, as Venus has no magnetic field and magnetosphere.

A large number of missions have contributed, partially or totally, to the Venus exploration, including the Soviet Venera 1-16 and the American Magellan, Mariner 2, 5, 10, Pioneer-Venus 1,  2 and Messenger. Europe contributes through the Venus Express probe, while the BepiColombo spacecraft is expected to launch in 2014.

LINKS:

The Magellan Project homepage:

             http://www2.jpl.nasa.gov/magellan/

The Soviet exploration of Venus:

             http://www.mentallandscape.com/V_Venus.htm

The Mariner – 5 mission:

             http://solarsystem.nasa.gov/missions/profile.cfm?MCode=Mariner_05

The Pioneer – Venus project:

             http://nssdc.gsfc.nasa.gov/planetary/pioneer_venus.html

The Messenger mission:

             http://messenger.jhuapl.edu/

The Venus Express mission:

             http://www.esa.int/SPECIALS/Venus_Express/

 The BepiColombo mission:

             http://www.rssd.esa.int/index.php?project=BEPICOLOMBO

PICTURES:

The Venusian surface as observed by the Magellan space mission.

An Ultraviolet image of Venus' clouds as seen by the Pioneer Venus Orbiter (NASA).

From http://pds.nasa.gov/planets/special/venus.htm  

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