EXPLORATION BEYOND THE MOON

Probes

Space research carried out in the second half of the decade while the shuttle was delayed and budgets were cut was done mainly by space probes. Probes, with no need for life support, could go further and endure harsher conditions than spaceflight involving humans. The various probe programs of the 1970s (all with romantic names: Mariner, Voyager, Viking, Pioneer) sent back information about the five nearest planets: Mercury, Venus, Mars, Jupiter, and Saturn. Uranus and Neptune would be reached in the next decade.

Martians

Some of the earliest and most eagerly awaited photos came from Mars. In the 1960s three of the Mariner probes had successfully flown by Mars and returned with pictures. But NASA hit the jackpot with Mariner 9 in January 1972: unlike previous space probes, this one orbited the planet. After a week of blinding dust storms, Mariner suddenly began sending back stunningly clear photos—7,329 of them. They were discouraging to those who hoped for suggestions of life on Mars; they showed that the long, canyonlike rills astronomers had observed were not "canals, nor were the seasonal dark bands" vegetation. Yet Mariner 9 mapped the whole surface of Mars before contact was lost, unexpectedly finding volcanoes and giving scientists detailed information about the topography of the planet. Two Viking probes, launched in 1975, found a way to see Mars from an even closer perspective: each carried a landing craft with its own photographic gear and a small biological laboratory. These produced panoramic shots of the pock-marked, rocky Martian surface, which were relayed by the still-orbiting Viking craft. The landers also ran tests on soil samples in an unsuccessful attempt to find signs of life. The Viking orbiters continued sending back aerial views of the planet, even after the landers ceased transmitting. One, Viking 2, continued sending photos until 1980.

Voyagers

The other richly successful space probe of the decade was Voyager 2, launched on 20 August 1977, the first human-made object to leave the solar system (in 1989, after twelve years of flight). It carried with it greetings, in virtually every human language, as well as the call of the humpback whale to whoever might find it. Due to an unusual alignment of planets, it was able to pass the four large outer planets before leaving the solar system. In its flight by Jupiter and Saturn, Voyager had the company of its twin, Voyager 1, traveling somewhat behind it. Both found the Jovian moons covered with ice, and Saturn's rings, composed of thousands of small rings, infinitely more complex than imagined. The photos, the first detailed glimpses of the outer planets, captivated the public and thrilled scientists, who were able to study Jovian weather patterns and the composition of Saturn's rings for the first time.