The idea that Mars, like the earth, might be the home of living beings has held our imagination since the turn of the century, when Percival Lowell thought he saw hundreds of canals crisscrossing the face of the planet, and took them as proof that Mars was inhabited.

Lowell was wrong. The canals never existed, as Mariner 9 photographs finally proved five years ago. But even though his evidence was mistaken, Lowell’s conclusion may yet be vindicated: the Viking landers have returned an impressive array of biochemical data which seems to show that some form of life really does exist on Mars.

The results of the Viking life-detection experiments have been more positive than most people expected. Dr. Robert Jastrow, director of NASA’s Goddard Institute for Space Studies, says, “Short of seeing something wiggling on the end of a pin, the case for life on Mars is now as complete as the Viking experiments could make it.”

But no one wants to make predictions about Martian life which might be proved wrong by later evidence; scientific reputations could too easily be damaged in the process. So the Viking scientists have been extremely cautious in interpreting the results of their biology experiments. And the official NASA position straddles the fence. As Viking scientist Dr. Carl Sagan of Cornell University puts it, “We have clues up to the eyebrows, but no conclusive explanations of what we're seeing.”

The Viking team has good reason to maintain this ambiguous tone in public pronouncements. After all, the discovery of any kind of extraterrestrial life will have profound and far-reaching effects; it is something which no scientist can afford to be wrong about. As The New York Times indicated in an editorial, “The scientists … are being understandably cautious—in fact, they are leaning over backward.”

This extreme cautiousness means that few people get an accurate impression of how exciting and portentous the experimental evidence is. To many, in fact, the published reports suggest that the biology results have been totally negative, or at best hopelessly inconclusive. But experiments are continuing at a brisk pace, both on Mars and in Earth-based laboratories, and the ambiguities may soon be resolved. We may, in fact, be close to the momentous occasion when NASA officials call a press conference to release the mindboggling and epoch-making news that Earth people are not alone, that we have reached out and made a tentative contact with an alien form of life.

Preliminaries over, the search for Martian life began on July 28, 1976, eight days after Viking I made its touchdown on Chryse Planitia, the Plain of Gold. On that day, at 3:30 A.M., the sampler arm reached out to dig into the surface of Mars. Whirring and clicking, the arm slowly unfurled from its storage compartment.

The arm, ingeniously designed, is made up of two curved strips of stainless steel, welded together and rolled up like a steel tape measure. Despite its flimsy appearance, it is surprisingly strong. It can push straight ahead with a force of forty pounds, and pick up a fairly large rock when extended to its full length of ten feet.

The soil samples were acquired by extending the arm at a slight downward angle and then thrusting forward to force the collector head, which resembles a small shovel with teeth, into the ground to a depth of just over an inch. The sampler's jaws then snapped shut to hold the soil, and the arm retracted to the lander body, where it dumped its scoops of soil into the openings for each of the Viking's three miniature automated laboratories. This operation took about four hours.

One soil sample was dumped into the hopper for the biology experiments, where it passed through a sieve before being funneled into three separate chambers—about a teaspoonful of soil for each of the three life detection experiments. The test chambers were then sealed against the outside environment, and the incubation began.

The Viking biology labs are very sophisticated machines, containing the most advanced set of remote-controlled instruments ev