Robotic exploration of Mars has been one of the persistent efforts of the space age. It began, just as lunar exploration had, in a race between the United States and the Soviet Unionto see who would be the first to place some sort of spacecraft near Mars. After four unsuccessful launches of what were believed to be Mars probes in 1960 and 1962, the Soviets successfully flew a spacecraft within 120,000 miles of Mars on June 19, 1964. Unfortunately, a communications failure several months before the flyby prevented the spacecraft from sending any data to Earth. The Americans were more successful.
This endeavor was not just an opportunity to best the rival in the Cold War; scientists in both the United States and the Soviet Union recognized the attraction of Mars for the furtherance of planetary studies. Smaller than Earth, but observed by astronomers for centuries and seen to have what appeared as climate changes on its surfaces, Mars had long been viewed as an abode of life. These observations brought myriad speculations about the nature of Mars and the possibility of life existing there in some form.
Of the two U.S. spacecraft launched to Mars in 1964, only one successfully found its way to its intended target. On July 15, 1965, Mariner 4 flew within 6,118 miles of Mars. The spacecraft returned 21 close-up photographs that showed lunar-style craters on the surface. Data returned also included measurements of the planet’s ionosphere and atmosphere, as well as surface temperature readings. These photographs dashed the hopes of many that life might be present on Mars, for the first close-up images showed a cratered, lunar-like surface. They depicted a planet without structures and canals, nothing that even remotely resembled a pattern that intelligent life might produce.
Mariner 6 and Mariner 7, launched in February and March 1969, each passed Mars in August 1969, studying its atmosphere and surface to lay the groundwork for an eventual landing on the planet. Their pictures verified the moon-like appearance of Mars and gave no hint that Mars had ever been able to support life. Among other discoveries from these probes, they found that volcanoes had once been active on the planet, that the frost observed seasonally on the poles was made of carbon dioxide, and that huge plates indicated considerable tectonic activity in the planet’s history. There was still hope, however, that we might yet find signs of life. NASA administrator James C. Fletcher, for example, commented on this possibility in 1975: “It is hard to imagine anything more important than making contact with another intelligent race. It could be the most significant achievement of this millennium, perhaps the key to our survival as a species.”
Between 1965 and 1969, NASA sent three Mariner probes on initial investigations of Mars. All of these were flyby missions that returned important scientific data about the planet:
- Mariner 4 – USA Mars Flyby – 260 kg – (28 November 1964 – 20 December 1967): Mariner 4 arrived at Mars on 14 July 1965 and passed within 6,118 miles of the planet’s surface after an eight month journey. This mission provided the first close-up images of the red planet. It returned 22 close-up photos showing a cratered surface. The thin atmosphere was confirmed to be composed of carbon dioxide in the range of 5-10 mbar. A small intrinsic magnetic field was detected. Mariner 4 is now in a solar orbit. (Successful)
- Mariner 6 – USA Mars Flyby – 412 kg – (24 February 1969): Mariner 6 arrived at Mars on 24 February 1969, and passed within 3,437 kilometers of the planet’s equatorial region. Mariner 6 and 7 took measurements of the surface and atmospheric temperature, surface molecular composition, and pressure of the atmosphere. In addition, over 200 pictures were taken. Mariner 6 is now in a solar orbit. (Successful)
- Mariner 7 – USA Mars Flyby – 412 kg – (27 March 1969): Mariner 7 arrived at Mars on 5 August 1969, and passed within 3,551 kilometers of the planet’s south pole region. Mariner 6 and 7 took measurements of the surface and atmospheric temperature, surface molecular composition, and pressure of the atmosphere. In addition, over 200 pictures were taken. Mariner 7 is now in a solar orbit. (Successful)
In addition there were several unsuccessful missions that attempted to flyby Mars in the early era:
- Mars 1960A – USSR Mars Probe – (10 October 1960): Failed to reach Earth orbit. (Unsuccessful)
- Mars 1960B – USSR Mars Probe – (14 October 1960): Failed to reach Earth orbit. (Unsuccessful)
- Mars 1962A – USSR Mars Flyby – (24 October 1962): Spacecraft failed to leave Earth orbit after the final rocket stage exploded. (Unsuccessful)
- Mars 1 – USSR Mars Flyby – 893 kg – (1 November 1962): Communications failed en route. (Unsuccessful)
- Mars 1962B – USSR Mars lander – (4 November 1962): Failed to leave Earth orbit. (Unsuccessful)
- Mariner 3 – USA Mars Flyby – 260 kg – (5 November 1964): Mars flyby attempt. Solar panels did not open, preventing flyby. Mariner 3 is now in a solar orbit. (Unsuccessful)
- Zond 2 – USSR Mars Flyby – (30 November 1964): Contact was lost en route. (Unsuccessful)
- Mariner 8 – USA Mars Flyby – (8 May 1971): Failed to reach Earth orbit. (Unsuccessful)
- Kosmos 419 – USSR Mars Probe – (10 May 1971): Failed to leave Earth orbit. (Unsuccessful)