Physical features

Venus is very similar to Earth in size, mass, and density. Its diameter is about 7,500 miles (12,100 kilometers). Scientists believe that Venus might have layers similar to those of the Earth: an inner core made of metal, a thick middle layer of rock, and a crust.

The surface of Venus was greatly shaped by lava from erupting volcanoes. Most of the surface consists of gently rolling plains, though there are also several lowland areas. In addition, Ishtar Terra and Aphrodite Terra are two highlands as big as continents. Maxwell Montes is the highest region on Venus.

Venus' atmosphere is made up mainly of carbon dioxide. The planet is covered by thick clouds that reflect the sunlight, making Venus very bright in the Earth's nightime sky. The clouds are composed mostly of sulfuric acid. They allow only a small amount of sunlight to reach the planet's surface. Because of this, the days on Venus are dim and overcast.

Although much of the sunlight is reflected, the heat energy from the sun does reach the surface. The large amounts of carbon dioxide and the heavy cloud cover trap this energy at the surface, making the planet very hot. The temperature on Venus is about 867° F (464° C) near the planet's surface. Venus is even hotter than Mercury, the planet closest to the sun. As a result, the surface of Venus is hot enough to melt lead. Rocks may even glow faintly red from their own heat.

Orbit and spin

Like all planets, Venus has two types of motion, known as orbit and spin. Unlike the other planets in the solar system (except Uranus), Venus spins on its axis in a clockwise direction. This means that a person on Venus would see the sun rise in the west and set in the east—the opposite of the situation on Earth. In addition, Venus spins on its axis very slowly. It takes 243 Earth days to complete one rotation. At the same time, Venus orbits the sun in about 225 Earth days.

The same side of Venus is always facing Earth when the two planets pass in orbit. Most of the planets travel around the sun in an elliptical, or oval, orbit. Venus' orbit is almost a perfect circle. (For more information on orbit and spin, see planets.)

Observation and exploration

Because of Venus' brightness in the night sky, it has been observed since ancient times. The Italian scientist Galileo made the first observations of Venus through a telescope in the early 17th century.

The greatest advances in the study of Venus have been made with unmanned spacecraft. More than 20 missions have visited the planet. The United States National Aeronautics and Space Administration (NASA) launched the Mariner 2 spacecraft in 1962. It became the first spacecraft to fly near another planet when it passed by Venus. In 1967, Mariner 5 flew even closer to Venus. It passed within only about 2,500 miles (4,000 kilometers) of the planet.

In 1970 the Soviet Union's Venera 7 landed on Venus. It was the first spacecraft to land on the surface of another planet and send data back to Earth. In 1975 Venera 9 and 10 became the first spacecraft to orbit Venus. The craft sent back close-up photographs of the planet's rocky surface.

NASA's Pioneer Venus 1 and 2 began orbiting the planet in 1978. Instruments aboard the craft used radar to reveal the planet's huge mountains and deep basins. From 1990 to 1994, NASA's Magellan spacecraft mapped Venus' surface in great detail. Data from Magellan suggested that the planet's surface is relatively young. Venus may still have active volcanoes in some places.