Exploring the MarsAbout 120 years ago Giovanni Schiaparelli announced the news about strange channels he had observed on Mars. Several other astronomers, among them an American, Percival Lowell, confirmed the observation. Since then, many hypotheses appeared intending to explain what the channels were and what purpose did they serve. Some of them were, in fact, quite attractive, like the one which assumed that the channels formed an enormous water system (the length of some channels approached 6,000 km) constructed by intelligent inhabitants of Mars. The Martians have indeed become heroes of many science-fiction novels, where they were usually depicted as tiny human-like creatures with a watering can strainer instead of the nose and aerials instead of ears.
More accurate optical investigation first and then still more precise research using space probes have fully discarded the existence of Martians and reduced to null the possibility of any form of life on the planet.
The exploration of Mars by space probes started in 1965, when Mariner 4 transmitted 22 images of the surface of Mars to laboratories on earth. The surface, seen at a close range, gave no impression of being inhabited. It resembled a moon landscape rather than a savanna. In the following seven years the American Mariners and the Russian Marses made possible an exact observation of the details on the planet's surface. The conclusions drawn from observation were quite simple. Firstly, no traces of channels nor of any activity of intelligent creatures have been found, neither have any signs of the existence of vegetation been established. Secondly, it turned out that the conditions on the surface are much more harsh than it had been expected. In particular, the atmospheric pressure on Mars was discovered to be very low, about 0.6% of the pressure on the earth surface. Huge differences between night and day temperatures (on the equator the temperatures range from 27 degrees Celsius at day to -70 degrees Celsius at night) and rare traces of oxygen in the planet's atmosphere are very unpropitious to the development of any complex forms of life. However, observation did not exclude the existence of very primitive forms of life on Mars such as viruses or bacteria. The problem could be decided by a thorough analysis of Martian soil. Unfortunately, at present there is no chance of importing samples from Mars. Hence, the only way to find an answer to this fascinating question is to perform the analyses on site - on the surface of the planet.
On July 20 and September 3 of 1976 two space probes called Viking 1 and 2 landed softly on the surface of the Red Planet. The probes can be considered the most complex space device ever constructed by humans. They contain tiny laboratories capable of investigating the biological activity of samples of the Martian soil. Altogether the Vikings performed four tests. The first test consisted in placing a sample of the soil in a sterilized chamber, which was then filled with the natural atmosphere of the planet, enriched with a very small amount of carbon dioxide and carbon oxide marked with the radioactive isotope C-14 and occasionally with some addition of water vapour; the sample was irradiated by a lamp imitating solar radiation. After 120 hours the gases were pumped out and the sample was heated to very high temperature to free all the organic compounds which may have been created. By measuring the quantity of C-14 contained in the compounds, conclusions can be drawn as to the rate of carbon assimilation. Carbon assimilation is one of the main processes occurring in living, even very primitive, organisms. In both cases the result turned out to be positive, which was even more significant when compared with the fact that samples which have been sterilized previous to analysis gave negative results.
The second test consisted in adding a culture medium marked with the radioisotope C-14 to a sample of Martian soil in order to verify whether gases containing this isotope are freed. To general surprise, the result was positive again.
The third test was intended to investigate the changes in the atmosphere above a soil sample imbedded in the medium. As was observed, carbon dioxide, oxygen and small amounts of nitrogen were liberated. The last test was meant to be an attempt to check the existence of life on Mars in the past. More specifically, soil samples were to be examined in search of the slightest trace of organic substance. Judging by the results of the first three experiments one might expect that the result would again be positive. However, a very subtle analysis showed no trace of organic substances in the samples collected near the probes whatsoever. How then should the results of the first three test be explained? Once more we got caught in a cosmic trap. We compared the test results to conditions on earth, while the surface of Mars is constantly exposed to ultraviolet rays, which, being almost fully absorbed by the atmosphere, do not reach the Earth. It turns out that this fact is of great significance. Indeed, a mixture of ferrous oxide and silicon oxide, the main components of Martian soil, was subject to ultraviolet radiation in a laboratory for a long period of time and the results obtained were the same as those of the tests performed by the Vikings.
Sceptics may still argue that there are primitive microorganisms on Mars which leave almost no organic traces, but the probability of this being so seems to be very small indeed.