The Soviet Union's Luna 3 solved an ancient mystery in 1959 when it snapped the first pictures of the far side of the Moon (left). The images showed a hemisphere with plenty of craters and jumbled mountains, but few of the dark volcanic plains that are visible on the side that faces Earth. Later, Luna 9 made the first soft landing on the Moon, while Luna 10 became the first craft to enter lunar orbit.

In 1962, the American Mariner 2 staged the first successful encounter with another planet when it flew past Venus. Its instruments recorded Venus' surface temperature and pressure, and the composition of its atmosphere and the clouds that envelope the planet. The next successful mission in the series, Mariner 4, snapped the first close-range pictures of Mars in 1965. The images revealed a Moon-like landscape.

Surveyor 1 snapped more than 10,000 pictures after it became the first American probe to land on the Moon, in 1966. Apollo 11 astronauts Neil Armstrong and Edwin Aldrin made the first manned landing on July 16, 1969, and five more landings followed. Samples of rock and soil helped scientists learn about the Moon's birth and history. Apollo 12 astronaut Pete Conrad poses beside Surveyor 3, which had landed two years earlier.

Only one spacecraft has visited Mercury. Mariner 10 flew by the planet three times in 1974 and 1975, and mapped about half of its battered, Moon-like surface, which is dominated by impact craters. Mariner found that Mercury's interior consists of a large iron-rich core, which generates a weak magnetic field around the planet.

The Soviet Venera 9 became the first spacecraft to transmit pictures from the surface of another planet when it touched down on Venus in 1975. And in a mission that began 15 years later, the American Magellan used cloud-penetrating radar to map more than 98 percent of Venus' surface. Its images revealed hundreds of volcanoes, giant lava flows, cracked domes of volcanic rock, and long canyons.

In 1976, NASA's Viking 1 and 2 landers became the first spacecraft to touch down safely on Mars. From opposite sides of Mars, they photographed and analyzed their environments (left), finding a surface of iron-rich clay and a frigid atmosphere battered by giant dust storms. Experiments designed to look for signs of life produced inconclusive results, which scientists interpreted as meaning the Martian surface is sterile.

Building on the success of the 1997 Sojourner rover, the Spirit and Opportunity rovers landed on Mars in 2003. Although their planned mission was just 90 Mars days long (about 92 Earth days), both rovers were still operating in 2007. Both found evidence that water had helped shape the Martian landscape in the distant past. Several American and European craft found similar evidence from Mars orbit.

See Also

Current and Ongoing Explorations

Explorations of the Outer Solar System

Explorations of Minor Bodies

This document was last modified: September 13, 2008