Earth and Venus are of almost same size and yet the comparison ends there. Apart from being neighbouring planets in the solar system there is hardly any parameter which matches when these two planets are compared.
Venus is the brightest object in the sky after moon. It is often referred to as a morning or evening star. Venus is known to man since prehistoric times. But much of what we know today about Venus has been discovered in the twenty and twenty first century.
Venus year is about 225 earth days. That is the time it takes to revolve once around the sun. But unlike earth day which is only 24 hours long, a Venus day is 243 earth days. So a Venus day is actually longer than a Venus year. Also unlike earth (rotates from west to east), Venus rotates in opposite direction, from east to west. Therefore sun rises in the west and sets in the east, only the day and nights are about 120 earth days long.
Because Venus rotates very slowly, its magnetic field is less developed than earth. Earth and Venus have similar inner cores but earth has a much stronger global magnetic field whereas Venus’s is concentrated near the poles. This is singularly due to faster rotation of earth around its axis.
Besides these peculiarities Venus exhibits extremely hot temperatures. There are two main reasons for this.
Venus atmosphere is made up of 96% carbon dioxide, 3% nitrogen and rest clouds of sulfuric acid droplets. There is trace amount of carbon monoxide and neon but no oxygen present and the atmosphere is a very volatile mixture of gases and clouds. The atmospheric pressure is about 90 times more as compared to earth. Such dense atmosphere plays a very crucial role.
To understand this let us consider how earth’s atmosphere behaves. The main gases here are 78% nitrogen, 21% oxygen, inert gases like Argon 1% and traces or carbon di oxide, ozone. The other gases like methane along with water vapour play an important role in maintaining earth’s temperature. The greenhouse gasses like Carbon di oxide, methane, ozone trap the heat emitting from the thermal infrared range. These gases keep on absorbing and emitting heat thus maintaining the earth temperature to what it is. The clouds also are a good absorber of heat and thus a non greenhouse entity which contributes to greenhouse effect.
Coming to Venus, one thing which is in abundance is the carbon di oxide. When 96% atmosphere is this greenhouse gas then the heat trapped is naturally many folds. Also the clouds, even though not made up of water vapour trap this heat. Carbon di oxide is a heavy gas it is 1.5 times denser than air at normal temperature and pressure. Such high concentration of Carbon di oxide is responsible for generating surface pressure of about 90 times more than earth’s atmosphere.
The second factor is presence of hundreds of active volcanoes on the surface of Venus. This fact only came to light once probes were sent to Venus. At such high temperatures landing a fully functional probe becomes impossibility. Venera 7 sent by Soviet Union in 1970 did land on Venus and managed to send data for 23 minutes before being destroyed by harsh Venus conditions.
Mapping the surface of Venus and study of its atmosphere is therefore done by probes orbiting Venus like the Magellan sent by NASA in 1994. Radar mapping done by Magellan suggests that Venus is covered with active volcanoes spewing lava all the times. Lava flows hundreds of miles due to the high atmospheric temperatures. The lava itself is a great source of heat. The heat contributed by these lava spewing volcanoes heat the Venus atmosphere even more and the dense air traps it thus keeping this planets temperatures high. As a result the surface temperature of Venus can go up to 470 degree centigrade.
Craters larger than 2 miles were detected but smaller craters are absent suggesting that small meteorites are totally burned by Venus’s dense atmosphere before they reach surface.
Lightning is also a common phenomenon but unlike earth lightning originates in the sulphuric acid clouds. With such a volatile and acidic atmosphere, Venus’s surface is subject to fierce cycle of corrosion.
Venus is named after the Roman goddess of Love and beauty, but in reality it is a very harsh place.
http://www.ajax.ehu.es/VEX/Venus.Earth/Venus.Earth.html
http://nssdc.gsfc.nasa.gov/planetary/factsheet/venusfact.html
http://solarsystem.nasa.gov/planets/profile.cfm?Object=Venus&Display=OverviewLong
