Viking: The U.S. invasion of Mars
Sen—Mariner 9’s success in delivering the first global survey of Mars only increased scientists' eagerness to learn more about Earth’s outer neighbour. The planet had long been suggested as a world where life might have adapted and still exist. NASA was keen to find out so sent a mission designed to look for Martian life.
What better way than to go there and touch the surface? And so it was that the agency’s next assault on the Red Planet was an ambitious double mission, each of which would combine an orbiting spacecraft with an octagonal base structure based on Mariner 9 but larger, with a lander, carefully sterilised to make sure it took no Earth bugs to Mars. The missions were named Viking 1 and Viking 2, and they became the first U.S. spacecraft to land on the Red Planet.
Viking 1 was launched first, on Aug. 20, 1975, from Cape Canaveral, Florida, lifted into the sky by a Titan IIIE-Centaur rocket. Viking 2 blasted off on Sep. 9, 1975, atop a similar launcher from the same spaceport. The two components of each mission travelled together on a journey lasting almost a year, locking onto the Sun and the star Canopus to stay properly oriented, before going into orbit around Mars—Viking 1 on June 19, 1976, and Viking 2 on August 7 the same year.
Part of the panorama from the Viking 1 lander, showing a rock-strewn, sandy landscape, giant boulder Big Joe, and a leg of the craft. Image credit: NASA/JPL
The orbiters’ enhanced views of the Martian surface led mission control to realise quickly that neither of the landing sites planned for the Vikings was suitable, and the search began for smoother and safer locations with fewer craters and other hazards. It took nearly a month before Viking 1’s lander was released for landing. After diving into the thin atmosphere, a protective shell was jettisoned and three landing legs extended. Then it parachuted to low altitude before three thrusters fired to allow it to touch down on the western slope of a region called Chryse Planitia, the Plains of Gold, at a location 22.3° north and 48° longitude.
As soon as the first spectacular images from the lander were received, it was clear that it had narrowly avoided disaster because a huge boulder, dubbed Big Joe, stood just a few meters away and would have destroyed the craft if it had landed on it.
Attention swiftly turned to bringing the Viking 2 lander safely down too, and this was achieved at its new site in Utopia Planitia at 47.7° north latitude and 48° longitude.
A photo of Mars built from a mosaic of Viking orbiter images. Image credit: NASA/JPL
Both landers were computer-controlled and powered by small nuclear generators. They stored data to tape recorders, then “phoned home” via the orbiters. The landers carried instruments to study the weather, plus the biology, chemical composition, magnetic and physical properties of the surface and atmosphere. The craft also took more than 1,400 photos of the rock-strewn terrain. A seismological experiment failed to work on Viking 1 and recorded just one possible quake on its sister lander, but all other experiments were successful.
The biological experiments, however, presented a puzzle. When soil was scooped up, heated in an oven and then had nutrients added, it fizzed with activity, but the result was not one of the outcomes expected. Though some scientists believe this was a sign of organic life, the general judgement was that it was a chemical reaction that did not indicate life. Mars’ thin atmosphere and lack of a protective magnetic shield means that it gets bombarded with radiation from the Sun, making it unlikely for life to be able to survive on or near the surface.
A spectacular view from above of the Solar System's largest volcano Olympus Mons, taken by the Viking 1 orbiter. Image credit: NASA/JPL
The Viking orbiters mapped 97 per cent of Mars, taking 52,000 images, and also found that the north polar cap was mainly made of water ice rather than carbon dioxide, as had been thought. Air pressure and the amount of water vapour in the atmosphere varied according to seasonal effects around the north pole. Other important findings from the mission included iron-rich clays on the surface, but no organic molecules, and the presence of significant quantities of nitrogen in the atmosphere. Observations of the density of Mars’ two tiny moons, Phobos and Deimos, suggested they were asteroids captured by the planet’s gravitational pull.
The Viking 2 orbiter operated until July 1978, and Viking 1 orbiter until August 1980. Viking 2’s lander failed in April 1980 and Viking 1’s stopped communicating in November 1982.