Introduction to Venus

NASA's Pioneer Venus probe captured this image of Venus' perpetual cloud layer in 1979.

At first glance, if Earth had a twin, it would be Venus. The two planets are similar in size, mass, composition, and distance from the Sun. But there the similarities end. Venus has no ocean. Venus is covered by thick, rapidly spinning clouds that trap surface heat, creating a scorched greenhouse-like world with temperatures hot enough to melt lead and pressure so intense that standing on Venus would feel like the pressure felt 900 meters deep in Earth's oceans. These clouds reflect sunlight in addition to trapping heat. Because Venus reflects so much sunlight, it is usually the brightest planet in the sky.

The atmosphere consists mainly of carbon dioxide (the same gas that produces fizzy sodas), droplets of sulfuric acid, and virtually no water vapor - not a great place for people or plants! In addition, the thick atmosphere allows the Sun's heat in but does not allow it to escape, resulting in surface temperatures over 450 C, hotter than the surface of the planet Mercury, which is closest to the Sun. The high density of the atmosphere results in a surface pressure 90 times that of Earth, which is why probes that have landed on Venus have only survived several hours before being crushed by the incredible pressure. In the upper layers, the clouds move faster than hurricane- force winds on Earth.

Venus sluggishly rotates on its axis once every 243 Earth days, while it orbits the Sun every 225 days - its day is longer than its year! Besides that, Venus rotates retrograde, or "backwards," spinning in the opposite direction of its orbit around the Sun. From its surface, the Sun would seem to rise in the west and set in the east.

Earth and Venus are similar in density and chemical compositions, and both have relatively young surfaces, with Venus appearing to have been completely resurfaced 300 to 500 million years ago.

Scientists used radar to peer through the clouds and map the surface of Venus.

The surface of Venus is covered by about 20 percent lowland plains, 70 percent rolling uplands, and 10 percent highlands. Volcanism, impacts, and deformation of the crust have shaped the surface. No direct evidence of currently active volcanoes has been found, although large variations of sulfur dioxide in the atmosphere lead some scientists to suspect that volcanoes may be active.

Although no rainfall, oceans, or strong winds exist to erode surface features, some weathering and erosion does occur. The surface is brushed by gentle winds, no stronger than a few kilometers per hour, enough to move grains of sand, and radar images of the surface show wind streaks and sand dunes. In addition, the corrosive atmosphere probably chemically alters rocks. Impact cratering is also affected by the dense atmosphere: craters smaller than 1.5 to 2 km across do not exist on Venus, largely because small meteors burn up in Venus' dense atmosphere before they can reach the surface.

A rare look at the surface of Venus from Russia's Venera 13 lander in 1981.

More than 1,000 volcanoes or volcanic centers larger than 20 km in diameter dot the surface of Venus. There may be close to a million volcanic centers that are over 1 km in diameter. Much of the surface is covered by vast lava flows. In the north, an elevated region named Ishtar Terra is a lava-filled basin larger than the continental United States. Near the equator, the Aphrodite Terra highlands, more than half the size of Africa, extend for almost 10,000 km. Volcanic flows have also produced long, sinuous chan-nels extending for hundreds of kilometers.

With few exceptions, features on Venus are named for accomplished women from all of Earth's cultures.

Venus' interior is probably very similar to that of Earth, containing an iron core about 3,000 km in radius and a molten rocky mantle covering the majority of the planet. Recent results from the Magellan spacecraft suggest that Venus' crust is stronger and thicker than had previously been thought. Venus has no satellites and no intrinsic magnetic field, but the solar wind rushing by Venus creates a pseudo-field around the planet.

Source: NASA