Ken Tapping, July 4, 2007

If you were an alien scientist, designing a simple experiment to search for life on Earth, one possibility would be to take a soil sample, add nutrients and watch for the waste products produced as the creatures in the soil enjoy their feast. Since soil here on Earth is teeming with microorganisms and creatures not so micro, one could assume the experiment would be a success. In the 1970's two Viking spacecraft headed for Mars, equipped to do just this experiment.

Both spacecraft landed successfully, deployed their antennas, established contact with Earth, and got to work. The two robots deployed scoops that grabbed handfuls of soil and tipped them into experiment chambers. These were sealed and nutrients added. Then the equipment waited to see if there was anything in that soil feasting on Earth food. The results looked positive; apparently something was eating it. However, the results were not exactly what would have been expected if the experiments had been conducted on Earth soil. So some scientists proposed that what was being seen was not life, but the results of the Sun's high-energy radiation doing things to the Martian surface.

Here on Earth we are protected from the Sun's ultraviolet radiation by a thick atmosphere and the ozone layer. At ground level, Mars' atmospheric pressure is about 0.4% of what it is here on Earth. That atmosphere provides almost no protection, and the idea was that the radiation would act on the iron and other oxides in the Martian surface to make peroxides. These chemicals are pretty strong stuff. We use weak solutions of hydrogen peroxide as antiseptics because they kill almost anything, and as bleaches, because they break down the molecules of dyes and colouring agents. Add some peroxides to our soils and pretty well everything would die. Therefore there could be no life on Mars, at least in the top layers of the soils because the peroxides would kill them.

It took about 30 years to realize that we were falling into our own trap of judging other planets using our standards for life. It is true that peroxides would be pretty lethal to us, but they could be wonderful things for alien life, in that they could provide energy, help process food, and provide oxygen. Peroxides could actually make life possible on Mars, where there is no free oxygen in the atmosphere for creatures like us to breathe.

We now know there is enough ice on Mars that, if melted, would cover the planet with an ocean around 11 metres deep. In all likelihood, we have only found a fraction of what is there. Millions of years ago, when Mars was warmer, there could well have been life, which evolved into tougher types as the planet dried and cooled.

So now we have to consider that we may well have found evidence of life on Mars, and it would certainly be worth going back for a better look. One other thing we might conclude is if there are any of Edgar Rice Burroughs' swashbuckling princesses on the Red Planet, they will probably be blondes.

Venus and Saturn appear very close together in the western sky during the evening. Jupiter is that bright object in the eastern sky. Mars rises in the early hours. The Moon will reach Last Quarter on July 7.

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Ken Tapping is an astronomer at the National Research Council Herzberg Institute of Astrophysics (NRC-HIA), and is based at the Dominion Radio Astrophysical Observatory, Penticton, BC, V2A 6J9 Tel (250) 493-2277, Fax (250) 493-7767,
E-mail: ken.tapping@nrc-cnrc.gc.ca