The Venera probes, dispatched by the Russians from 1966 to 1982, presented not a lush jungle, but a dry, hellish world almost devoid of oxygen and hot enough to melt lead. Although the probes were built sturdy as diving bells, each could take photos and obtain data for only about an hour before being destroyed by the heat and pressure. Scientists theorize that Venus fell victim to a runaway greenhouse effect — excess carbon dioxide trapping solar heat under the blanket of its atmosphere. Many questions remain to be answered about Venus. Was its climate once more temperate? And, if so, what went wrong? Was there life there in the past?

The Surface

Clouds

Volcanism

Terrain

Discovery: Because Venus is so bright — the brightest light in Earth's sky except for the Sun and our Moon, it was likely recognizable in early history as a unique feature in the sky. In 1610, Galileo Galilei was the first to note that Venus had a visible disk and phases like the Moon. Size: Venus is the second planet from the Sun and the sixth largest in our solar system. Orbit: Venus orbits the Sun at an average distance of 108,200,000 kilometers from the Sun. A year on Venus is approximately 225 Earth days. Comparison to Earth: Venus and Earth have roughly the same size and mass. At its equator Venus is 12,104 kilometers in diameter (or 0.95 times that of the Earth), and its mass is 0.81 times that of the Earth. Both planets also have few craters, indicating relatively young surfaces. The planets also have similar density and composition as well. Comparisons of the two planets' rotations, however, illustrate a key difference. Venus rotates on its axis in a direction opposite that of the Earth and the other planets of our solar system and takes 243 Earth-days for a complete rotation. One revolution around the Sun for Venus takes 225 Earth days. Because Venus takes longer to rotate on its own axis than to complete a journey around the Sun, one day on Venus is slightly longer than one year there! Terrain: 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 highest point on the planet, lying in the Maxwell mountains, rises about 11 kilometers above average surface elevation. The Maxwell range, named after physicist James Clerk Maxwell, is the only Venus feature named after a man. All other features on the planet are named after women, following planetary nomenclature rules established by the International Astronomical Union. Data collected by Magellan's imaging radar shows that much of Venus is covered by lava flows. There are several large shield volcanoes (similar to Hawaii) 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 quiet for the past few hundred millionyears. Water: At one time, Venus may have had large amounts of water — much like Earth, but now it is a dry, barren landscape. In fact, when it "rains" on Venus (its rain consists primarily of sulfur and carbon dioxide), any water evaporates before it ever hits the ground.

Exploration: Numerous U.S. space missions have visited Venus, beginning with a flight past the planet by the U.S. Mariner 2 in 1962. Mariner 5 flew past Venus in 1967 and Mariner 10 in 1974. In 1978 two U.S. spacecraft were sent there. Pioneer Venus 1 orbited the planet, collecting data on surface heights and returning radar images, while Pioneer Venus 2 released three probes to the surface to collect atmospheric data. The most recent U.S. mission to Venus, Magellan, launched from the Space Shuttle Atlantis on May 4, 1989 and entered Venus' orbit on August 10, 1990. The Magellan spacecraft remained in Venus' orbit collecting data for four years, and mapped 99 percent of the planet's surface utilizing a state-of-the-art radar. On October 12, 1994 the Magellan spacecraft entered Venus' dense atmosphere and disintegrated. The former Soviet Union has had an active Venus exploration program with its sixteen Venera missions conducted between 1961 and 1983. These explorations included orbiters, landers, and balloon studies of the planet's atmosphere. In 1985, the Soviet Union missions Vega 1 and Vega 2 also conducted flybys of Venus. The Interior: The interior of Venus is probably very similar to that of Earth: an iron core about 3000 km 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. Atmosphere: There are several layers of clouds many kilometers thick composed of sulfuric acid. These clouds completely obscure our view surface. The atmosphere is composed mostly of carbon dioxide. There are strong winds — up to 350 kilometers per hour — at the cloud tops, but winds at the surface are very slow, no more few kilometers per hour. Two Venera spacecraft carrying lightning detectors recorded massive lightning strikes in the Venus atmosphere, occuring at an average rate of more than 10 times per second. Probes from the Pioneer Venus mission discovered that, below the clouds, the atmosphere contains about 0.1 to 0.4 percent water vapor and 60 parts per million of free oxygen. These components indicate that Venus may have had abundant water at one point early in its history, water that has since been lost. Temperature: Temperatures on the planet's surface average 462 degrees Celcius (864 degrees Fahrenheit). Magnetic fields: Venus lacks any magnetic field, perhaps because of its excruciatingly slow rotation. Satellites: Venus has no satellites (moons). More Information: Learn more about Venus and its relationship to Earth in an interview with comparative planetology expert David Grinspoon.