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).
Mariner 9 took detailed photographs of Mars from orbit in 1971.
Photo: The Mariner 2 spacecraft (NASA/JPL)
Unmanned probes explore the inner Solar System.
The probe sees Mars's moons, volcanoes.
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.
Scientists are surprised to see that Mars is Moon-like.
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 US probe sees ancient craters on Mars.
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.
A series of missions finds astonishing features on the Red Planet.
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.
In 1962 some thought Venusian life was possible.
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 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 planetary orbiter, and the first gravity assist maneuver.
Of the ten vehicles in the Mariner series, seven were successful. The planned Mariner Jupiter-Saturn 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.
The total cost of the Mariner program was approximately $554 million.