Planet Profile - Venus
A closer Look at Venus
Three large impact craters with diameters ranging from 37 km (23 mi) to 65 km (40 mi) are visible in the fractured plains. Features typical of meteorite impact craters are also visible. Rough radar-bright ejecta surrounds the perimeter of the craters; terraced inner walls and large central peaks can be seen. Crater floors appear dark because they are smooth and have been flooded by lava. Domes of probable volcanic origin can be seen in the southeastern corner. The domes range in diameter from 1-12 km (0.6-7 mi); some have central pits typical of volcanic shields or cones.
The Geography of Venus
Most of Venus' surface consists of gently rolling plains with little relief. There are also several broad depressions: Atalanta Planitia, Guinevere Planitia, Lavinia Planitia. There two large highland areas: Ishtar Terra in the northern hemisphere (about the size of Australia) and Aphrodite Terra along the equator (about the size of South America). The interior of Ishtar consists mainly of a high plateau, Lakshmi Planum, which is surrounded by the highest mountains on Venus including the enormous Maxwell Montes.
Vulcanism on Venus
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.
Shield Volcano - Sif Mons
Located on the slopes of Sif Mons, this area displays a simple sequence of events. The small shield volcanoes, features commonly found on Earth, are no more than 5 km (3 mi) in diameter. The dark background plains and the shield volcanoes both formed from the eruption of very fluid lava. Over time, several layers of lava flows covered each other, each one successively brighter, indicating that they became blockier in texture over time. The summits of the shield volcanoes protrude from the flows. Once the lava flows were in place, fractures formed as the new surface expanded.
Beneath The Veil of Venus
Venus is the second planet from the Sun and the sixth largest. It is the brightest object in the sky except for the Sun and the Moon. Since Venus is an inferior planet, it shows phases when viewed with a telescope from the perspective of Earth. Venus was named for the Roman goddess of love. Galileo's observation of this phenomenon was important evidence in favor of Copernicus's heliocentric theory of the solar system.
The bluish hue of Venus is an effect of the colorization technique used to enhance subtle contrasts in cloud patterns and indicates that this image was taken through a violet filter. Features in the sulfuric acid clouds near the top of the planet's atmosphere are most prominent in violet and ultraviolet light. This image shows the east to west cloud banding and the brighter polar hoods.
There are strong winds that flow from east to west at about 370 kph or 230 mph at the cloud tops. However the wind speed at the surface is very slow, usually no more than a few kilometers per hour.
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.
The pressure of Venus' atmosphere at the surface is 90 atmospheres. This is 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 sulfuric 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 which is hot enough to melt lead. Venus' surface is actually hotter than Mercury's despite being nearly twice as far from the Sun.
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.
Venus Resource Links
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