Pioneering Venus
An ultraviolet image of Venus' clouds as seen by the Pioneer Venus orbiter in 1979.
Pioneer Venus used an orbiter and several small probes to study the planet from above and within the clouds. This image is from the orbiter.
Image Credit: NASA

 

 

Venus

The ancient Greek goddess of love, is the second planet from the Sun and 6th in size.

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.

Although we cannot normally see through Venus' thick atmosphere, NASA's Magellan mission to Venus used radar to image the surface, and Galileo used infrared mapping to view mid-level cloud structure.

Like Mercury, Venus can be seen periodically passing across the face of the Sun. These transits of Venus occur in pairs with more than a century separating each pair. Since the telescope was invented, transits were observed in 1631, 1639; 1761, 1769; and 1874, 1882. On June 8, 2004, astronomers worldwide saw the tiny dot of Venus crawl across the Sun; the second in this pair of early 21st-century transits will occur June 6, 2012.

The atmosphere consists mainly of carbon dioxide, with clouds of sulfuric acid droplets. Only trace amounts of water have been detected in the atmosphere. The thick atmosphere traps the Sun's heat, resulting in surface temperatures over 470 degrees Celsius (880 degrees Fahrenheit). Probes that have landed on Venus have not survived more than a few hours before being destroyed by the incredibly high temperatures.

The Venusian year (orbital period) is about 225 Earth days long, while the planet's rotation period is 243 Earth days, making a Venus day about 117 Earth days long. Venus rotates retrograde (east to west) compared with Earth's prograde (west to east) rotation. Seen from Venus, the Sun would rise in the west and set in the east. As Venus moves forward in its solar orbit while slowly rotating "backwards" on its axis, the cloud-level atmosphere zips around the planet in the opposite direction from the rotation every four Earth days, driven by constant hurricane-force winds. How this atmospheric "super rotation" forms and is maintained continues to be a topic of scientific investigation. About 90 percent of the surface of Venus appears to be recently solidified basalt lava; it is thought that the planet was completely resurfaced by volcanic activity 300 to 500 million years ago.

Sulfur compounds, possibly attributable to volcanic activity, are abundant in Venus' clouds. The corrosive chemistry and dense, moving atmosphere cause significant surface weathering and erosion. Radar images of the surface show wind streaks and sand dunes. Craters smaller than 1.5 to 2 kilometers (0.9 to 1.2 miles) across do not exist on Venus, because small meteors burn up in the dense atmosphere before they can reach the surface.

More than 1,000 volcanoes or volcanic centers larger than 20 kilometers (12 miles) in diameter dot the surface of Venus. Volcanic flows have produced long, sinuous channels extending for hundreds of kilometers. Venus has two large highland areas:

Ishtar Terra, about the size of Australia, in the north polar region; and Aphrodite Terra, about the size of South America, straddling the equator and extending for almost 10,000 kilometers (6,000 miles). Maxwell Montes, the highest mountain on Venus and comparable to Mount Everest on Earth, is at the eastern edge of Ishtar Terra.

Venus has an iron core about 3,000 kilometers (1,200 miles) in radius. Venus has no global magnetic field, though its core iron content is similar to that of Earth, Venus rotates too slowly to generate the type of magnetic field that Earth has.

 

Venus Transit
Date: 06.08.2004
NASA's TRACE satellite captured this image of Venus crossing the face of the Sun as seen from Earth orbit. The last event occurred in 1882. The next Venus transit will be visible in 2012.
Image Credit: NASA

 

 

Venus - Computer Simulated Global View Centered at 180 Degrees East Longitude
This global view of the surface of Venus is centered at 180 degrees east longitude. Magellan synthetic aperture radar mosaics from the first cycle of Magellan mapping are mapped onto a computer-simulated globe to create this image. Data gaps are filled with Pioneer Venus Orbiter data, or a constant mid-range value. Simulated color is used to enhance small-scale structure. The simulated hues are based on color images recorded by the Soviet Venera 13 and 14 spacecraft. The image was produced by the Solar System Visualization project and the Magellan science team at the JPL Multimission Image Processing Laboratory and is a single frame from a video released at the October 29, 1991, JPL news conference.

 
Venus data
Discovered By Known by the Ancients
Date of Discovery Unknown
Average Distance from the Sun 108,208,930 km
Perihelion (closest) 107,476,000 km
Aphelion (farthest) 108,942,000 km
Equatorial Radius 6,051.8 km
Equatorial Circumference 38,025 km
Volume (Earth = 1) 0.88
Mass (Earth = 1 0.815
Density 5.24 g/cm3
Surface Area 460,200,000 km2
Equatorial Surface Gravity 8.87 m/s2
Escape Velocity 37,300 km/h
Sidereal Rotation Period (Length of Day) -243 Earth days (retrograde)
Sidereal Orbit Period (Length of Year) 0.615 Earth years
Mean Orbit Velocity 126,077 km/h
Orbital Eccentricity 0.0068
Orbital Inclination to Ecliptic 3.39 degrees
Equatorial Inclination to Orbit 177.3 degrees
Orbital Circumference 675,300,000 km
Minimum/Maximum Surface Temperature 462 °C
Atmospheric Constituents Carbon Dioxide, Nitrogen
Moons 0
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