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Alien life - Where would we look?

Ken Tapping's weekly astrophysics column from the Herzberg Institute

Here on Earth we find living creatures almost everywhere. We find them in the deserts, at the poles, in near-boiling hot springs, in far hotter than boiling black smokers on the sea bottom, and in cavities in the rock, kilometres underground. Knowing this, the idea of life somewhere on Mars does not sound far-fetched. However, such life could be very exotic and hard to get to. The Big Question is then “How do we look for it?” It probably won’t be a case of having a Martian walk up to the camera on one of the Mars Rovers and wave to us, or to walk up to a visiting astronaut and ask to be taken to our Leader.

Life on Earth is driven by chemistry, and many of the chemicals involved are highly-reactive and are unlikely to form in nature, or if they do, occur at very low concentrations. It is inevitable that chemicals processed by living things find their way into the land, ocean and atmosphere. Some remain for long periods; others promptly react with something and are removed. So the presence of these chemicals on a planet is evidence of life.  Some chemicals end up sequestered in the rocks and are evidence of life in the past. Others are so highly reactive and must be continually topped up, and are evidence of living creatures being present now.

Calcium carbonate is a chemical formed in oceans and its presence on Mars indicates a lot of water was present in the past. However, many marine creatures extract it from their environment to make shells and other body structures. When they die their remains fall to the bottom, producing huge deposits of concentrated calcium carbonate. Their presence raises a strong flag for life.

On Earth, calcium carbonate exists in rocks such as chalk, as in the “White Cliffs of Dover”, and limestone. chalk is composed of countless small shells, and limestone is made up of coral fragments and remains of small sea creatures. Amber is fossilized resin and an indicator of past life.

Oxygen is produced by plants. It is so reactive that if not continuously replaced it would rapidly combine with something to form a more inert substance. Mars’oxygen is now largely locked up in the red minerals covering its surface, which are rich in iron oxide. Another substance that raises questions if present in a planet’s atmosphere is methane, which is produced by living creatures during life and when they decay after death.

The possibility of life deep underground is intriguing. The question is, where do we look? We won’t be mining on Mars for some time yet.  However, it turns out that large craters may be good places. We are familiar with asteroid impacts as wipers-out of life. However, by pulverizing the rocks to great depths, they allow water and nutrients to penetrate deep down, to the benefit of life forms in the rock. It might also bring either the living creatures or their by-products closer to the surface, where we can more easily search for them.

Jupiter is low in the sunset glow; Venus is higher up and brilliant, and will be nicely close to the Moon on the 24th.  Mars is high in the south, close to the brightish star Regulus, in Leo; Saturn rises about 8 p.m., quite close to Spica, the brightest star in Virgo. The Moon will reach first quarter on the 29th.

Ken Tapping is an astronomer with the National Research Council’s Herzberg Institute of Astrophysics, and is based at the Dominion Radio Astrophysical Observatory, Penticton, BC.