Has life existed on Mars?

Ever since the 19th century, people have speculated seriously about the possibility that living organisms might have come into existence on the red planet. Tonight, like hosts of observers throughout the world, I shall be waiting anxiously to learn if Nasa's Phoenix lander has arrived safely on our neighboring planet, and deployed correctly its rich assortment of scientific equipment.

There are now several excellent videos describing the Mars rovers named Spirit and Opportunity, which landed respectively on 4 and 24 January 2004. The following video uses synthetic images to indicate what should happen tonight if everything goes fine for Phoenix:



The cosmologist Giordano Bruno was convinced that life existed beyond the planet Earth:

For no reasonable mind can assume that heavenly bodies that may be far more magnificent than ours would not bear upon them creatures similar or even superior to those upon our human Earth.

For expressing thoughts of this kind, the Inquisition accused Bruno of heresy, and he was burnt at the stake in Rome, thereby becoming the world's first martyr for science.

These days, people have ceased imagining that Mars might be populated by little green creatures who built canals. We have few ideas on the nature of self-replicating organisms that might exist elsewhere in the universe. Even the great Charles Darwin [1809-1882] may have been wrong when he suggested that life probably started, here on Earth, in a "warm little pond ". For all we know, life might be able to spring into existence in a volcano, or deep inside clouds of gas. But the presence of liquid water would appear to be conducive to the development of primitive forms of life in a context of carbon-based chemistry, as on Earth. The Phoenix laboratory might be able to inform us if this was, or is, the case on Mars.