Venus - A Snapshot



Diameter: 7,521 miles (12,104km).

Mass: 0.82 Earth masses

Rotation period: 243.0 days, retrograde.

Inclination of equator to orbit: 177.4 degrees.

Mean orbital speed: 22 Miles per second (35 km/s)

Mean distance from the sun: 67 million miles (108 million km)





Given its closer proximity to the sun one would expect Venus to be somewhat warmer than the earth. In fact it is an inferno, with a surface temperature of 890F, a temperature hot enough to melt lead and zinc, it is actually hotter than Mercury's surface, despite being nearly twice as far from the sun. The explanation for this disparity lies in Venus' atmosphere of carbon dioxide, a layer so dense that the pressure at the surface of the planet is nearly a hundred times that of the earth. This thick blanket traps the suns heat at the planet's surface, producing an extreme greenhouse effect, and thus scorching temperatures. Cloud layers stretch upward from an altitude of 30 miles above the surface, yet these are no ordinary clouds, they consist almost entirely of sulfuric acid droplets, and are spread relatively uniformly across the planet.

The first space craft to visit the planet was Mariner 2 in 1962, yet it has been subsequently visited by many others including Pioneer Venus, Venera 7 (the first space craft to land on another planet) and Venera 9, which returned the first images of the surface. However in more recent times the orbiting space craft Magellan has produced detailed maps of the surface using radar.


Earth's crust is recycled and shaped by plate tectonics, in which the continents ride on huge plates. Between 1990 and 1992 radar survey by the Magellan orbiter showed a much different process at work on Venus. Dome like structures are evidence of upwellings of lava in the planets mantle and these, together with widespread volcanic activity, are largely responsible for recycling the crust and sculpting a desolate landscape. Nearly 85% of the surface consists of flat lava plains which resemble the basaltic Maria, or seas of the moon. There are huge volcanoes and mountain ranges, the Maxwell mountains rise nearly 7.5 miles above the surrounding plains. The planets two great landmasses are Aphrodite Terra, which girths a portion of the planet from the equator into the southern hemisphere, and Ishtar Terra, in the high latitudes of the Northern hemisphere. Venus has an estimated 900 impact craters, all larger than 2 miles in diameter, due to the fact that the dense atmosphere has protected the surface from small asteroids and comets. Magellan's images also show a wide variety of additional features, including pancake volcanoes, which seem to be very thick eruptions of lava, and coronae, which seemed to be collapsed domes over large magma chambers.

Venus rotates very slowly, once every 243 earth days, which is 18 days longer than it takes to rotate around the sun. Furthermore it spins not from west to east like the other planets, but from east to west. This slow retrograde motion has a strange effect on the Venusian calendar. If you were on Venus you would see the sun rise in the west, cross the sky and set in the east, some 59 earth days later. It is thought that maybe some earlier impact between Venus and another body may have resulted in this backward course.

Venus probably once had large amounts of water like earth, but it all boiled away, of which Earth may have suffered the same fate had it been just a little closer to the sun. The interior of Venus is probably very similar to that of the earth, an iron core about 3000km in radius, a molten rocky mantle comprising the majority of the planet. Recent results from the Magellan gravity data indicate that Venus' crust is stronger and thicker than had previously been assumed. Like earth, convection in the mantle produces stress on the surface which is relieved in many relatively small regions instead of being concentrated at plate boundaries as is the case on earth. Lastly this planet has no magnetic field or satellites.



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