Mars was a natural target for exploration once we could send probes through interplanetary space. Mariner 4 delivered the first close-up pictures of another planet on 15 July 1965 (July has been a big month for Mars spacecraft). The 11th of its 21 TV images (right) was especially noteworthy for showing many moonlike craters, which deflated expectations that still hadn't quite faded from the age of canals ("Craters? Yuck. We've seen craters. It must be just like the moon!"). This was followed by the twin flyby missions of Mariners 6 and 7, arriving in July and August 1969. By now NASA could add a "far-encounter" phases, bridging the gap between Earth-based views and close-up detail. Mariner 7 paid special attention to the south polar cap. Still, as luck would have it, these three missions managed to examine the most boring possible slices of Mars.

Our modern view of Mars started to emerge only with the global mapping made possible when Mariner 9 became the first artificial satellite of another planet in 1971 (well, the first one we had anything to do with...). After waiting out a planet-wide dust storm, it delivered images of practically the whole Martian surface. As the dust settled, Mariner 9 revealed a whole new world. Enormous volcanoes, the vast canyons (ever wonder why it's called Vallis Marineris?), and, most interesting, evidence that water once flowed in sufficient quantity to leave not just channels, but flood deposits.

The enormous interest in extraterrestrial life, and the long-standing notion that Mars was the best place to look, led to the Viking program - a pair of orbiters and landers whose purpose was to analyze the Martian soil. Viking 1 was originally scheduled to touch down on 4 July 1976 (the 200th anniversary of the Declaration of Independence), but was delayed until 20 July by another dust storm (but that's an OK anniversary date too). Lander 1 has the distinction of being the first successful soft landing on Mars (the Soviet probe Mars 3 having made it to the surface in 1971 but failed before returning any data beyond that fact). Each lander carried stereo cameras, meteorological instruments, and an extendible scoop to feed soil into three chemical experiments which had been designed to detect Earthlike organisms through searching for organic compounds, generating growth through nutrient solutions, and measuring repiration with tagged substances. One said yes, one said no, one was equivocal, so most scientists ( though not all) have regarded the evidence as easier explained by the peculiar Martian surface chemistry. The landers operated through an entire Martian year, and the Viking 2 orbiter continued in operation for a decade. Together the mission pieces yielded more than 50,000 images.

The 1997 landing (July 4, in fact) of the Mars Pathfinder spacecraft and its Sojourner rover captured wise public attention. This was one of the first news events in the Web, generating then-unprecedented millions of hits per day. The landing would have been something to watch, as the probe cut away its parachute, inflated air bags, and bounced and rolled to a stop. Mostly a technology demonstrator, the Pathfinder probe (now the Carl Sagan Memorial Station) also carried a set of filters to allow discriminating various kinds of rock and soil, while Sojourner was equipped with an X-ray experiment that enabled it to derive the chemical (though not minerological) makeup of individual Martian rocks. This demonstrated, for example, that the Martian meteorites found on Earth really did belong to Mars. The landing site was chosen with an old geologists' trick, picking an area which showed evidence of having once been at the outlet of a flood where rocks from many locations might be left. The most visually attractive results from the Pathfinder mission were a high-resolution panorama of the landing site:

views from Sojourner looking back at the lander which had carried it safely:

and movies of rover operations on the surface, shown below.

Currently returning spectacularly detailed images of Mars (think of it as a low-budget reconnaissance satellite) is Mars Global Surveyor, in orbit since September 1997. MGS carries two cameras and a laser altimeter, which have been used to examine the surface in new detail (not to mention create a great new National Geographic map). Some important questions that it's addressed so far have been

Last changes: August 2003