NASA's Mariner programme sent unmanned probes to study planets in the inner Solar System.
In 1962 Mariner 2 became the first probe to fly past a planet (Venus).
In 1964 Mariner 4 flew by Mars and returned the first close-up images of the Red Planet.
Mariner 9 took detailed photographs of Mars from orbit in 1971.
Mariner 10 became the first spacecraft to visit Mercury after it was launched in 1973.
Photo: The Mariner 2 spacecraft (NASA/JPL)
Prior to Mariner 2's 1962 flyby of Venus, some scientists such as Dr Carl Sagan thought that conditions on the planet might favour life. However, the probe's instruments showed that the cloudy planet's surface was extremely hot, greatly reducing the chance that anything could survive there.
The unmanned Mariner missions gradually revealed Mars's extreme landforms. Perhaps most impressive was Olympus Mons, a volcano three times the size of Mount Everest.
The Mariner 4 probe arrived at Mars in July of 1965, returning the first close-up photographs of the planet's surface as it flew by. The spacecraft showed scientists a barren, cratered area on Mars devoid of any signs of life.
Viewing parts of Mars missed by previous probes, Mariner 9 revealed three huge volcanoes and a massive canyon, now estimated to be 5 miles (8km) deep and over 1,800 miles (3,000km) long. The probe also took photographs of Mars's moons, Phobos and Deimos.
The handful of fuzzy black and white photographs taken by Mariner 4 in 1965 showed NASA's scientists a Martian surface covered with craters. This was evidence of a lack of recent weathering and erosion on the Red Planet.
The Mariner program was a program conducted by the American space agency NASA in conjunction with Jet Propulsion Laboratory (JPL) that launched a series of robotic interplanetary probes designed to investigate Mars, Venus and Mercury from 1962 to 1973. The program included a number of firsts, including the first planetary flyby, the first pictures from another planet, the first planetary orbiter, and the first gravity assist maneuver.
Of the ten vehicles in the Mariner series, seven were successful and three were lost. The planned Mariner 11 and Mariner 12 vehicles evolved into Voyager 1 and Voyager 2 of the Voyager program, while the Viking 1 and Viking 2 Mars orbiters were enlarged versions of the Mariner 9 spacecraft. Other Mariner-based spacecraft, launched since Voyager, included the Magellan probe to Venus, and the Galileo probe to Jupiter. A second-generation Mariner spacecraft, called the Mariner Mark II series, eventually evolved into the Cassini–Huygens probe, now in orbit around Saturn.
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