Spacecraft look beyond the bland appearance of our solar system's planet, revealing a complex, hellish world that may tell us much about Earth's past and future
For a planet named in honor of mythology's ultimate supermodel, Venus sure is camera shy.
Ancient astronomers named the brightest planet in the night sky Venus in honor of the Roman goddess of love and beauty. We know now that Venus shines so bright because the planet's perpetual layer of toxic yellowish-white clouds reflect so much sunlight. Only the Moon and Sun are brighter in our sky.
Spacecraft images of Venus in various parts of the electromagnetic spectrum reveal cloud patterns, but in general the planet named for beauty is a featureless Earth-sized ball when viewed from space.
The first mission to Venus - NASA's Mariner 2 - didn't even take pictures. But the information it sent back to Earth in 1962 during a 42-minute flyby was stunning.
The robotic probe - the first successful mission to another planet - found temperatures on the surface of Venus were hot enough to melt lead - nine times hotter than expected. It revealed the planet had no protective magnetic field.
"Instead of being a nice place to go visit, it was hell incarnate," said Kevin Baines, an American planetary scientist on the science team of the latest Venus mission, the European Space Agency's Venus Express.
The toxic carbon dioxide atmosphere is so dense the surface pressure was equal to those in the depths of Earth's oceans. The planet sluggishly rotates in the opposite direction of the other planets so the Sun rises in the West and sets in the East.
What lay under Venus' thick clouds remained a mystery until 1975 when the Soviet Union's sturdy Venera 9 spacecraft survived a descent through Venus' dense atmosphere and snapped a black and white photo of the planet's superheated rocky surface. The grainy images were the first sent back from another planet.
Later missions revealed what appeared to be the orangish-red hues of Venus' volcano-scorched surface. The true color of the surface rocks is difficult to judge because the planet's atmosphere filters out blue light. Orbiters meanwhile managed to coax details of clouds using enhanced imagery.
But it wasn't until the 1990s that planetary scientists finally got their first good look at the whole of Venus. NASA's Magellan spacecraft used radar to penetrate the clouds and map 98 percent of the planet's surface.
The images were used to make 3D models of hundreds of volcanoes that have covered most of the planet in basaltic lava. Other spacecraft and Earth-based observers have peered through gaps in the clouds with infrared mapping.
Throughout history, Venus helped put Earth in its place in the universe.
Four hundred years ago, Galileo Galilei's observations of the phases of Venus - similar to those of Earth's Moon - were evidence that Venus orbited the Sun. The discovery contributed to the downfall of the centuries-old belief that the Sun and planets revolved around Earth.
Observations of Venus as it crossed the face of the Sun - a transit - the 1760s led to the first good estimate of the distance of the Sun from Earth. The next Venus transit is on June 5-6, 2012.
Discoveries - and new questions - come a lot faster in the space age.
Spacecraft data has led to a better understanding of so-called greenhouse warming. Venus' intense surface temperature - over 470 degrees Celsius (880 degrees Fahrenheit) - is caused by a runaway greenhouse effect (the Sun's heat is trapped by the planet's thick mostly carbon dioxide atmosphere).
On Earth, scientists have found evidence greenhouse warming is melting polar ice caps and contributing to troubling climate changes. Man-made emissions have caused the carbon dioxide gases that cause the greenhouse effect to increase about 30 percent on Earth since humanity's industrial age began.
Scientists are trying to determine why Venus, which appears to have started out much like Earth, ended up with so much deady carbon dioxide in its atmosphere. The answer may help prevent further buildup on Earth.
Earth's superheated sister planet remains an intriguing target for exploration.
It is possible warm oceans existed on Venus for billions of years before they were somehow lost into space. That means Venus, like Mars and Jupiter's icy Moon Europa, is a prime target to hunt for signs of life beyond Earth - even though it may have been extinguished billions of years ago.
The planet provides a place to study how the lack of a magnetic field affects planetary evolution - unlike Earth where our magnetic field protects us from solar storms. It is also the only other planet in our solar system that may still have active volcanoes.
Understanding how the evolution of Earth and Venus - which share a prime spot in the neighborhood of our star, the Sun - will help scientists determine the future of Earth and aid in the search for habitable worlds in distant solar systems.
"Venus has a lot to teach us," Baines said. "It is really Earth gone awry."
Venus Education Activities
Last Updated: 2 February 2011