Astrobiologists are still searching for the smoking gun - the hard, irrefutable evidence that there were once not only the theoretical preconditions for life on Mars (what one might call circumstantial evidence of life), but that primitive life once existed on the surface of the red planet. Thus far, there is mounting evidence that the surface of Mars was once home to water, and that the planet could have been much more friendly to life as we recognize it - carbon-based, and living in water - than the same surface is today.
Mounting circumstantial evidence is different than proof. Nevertheless, it is time to at least begin thinking about how evidence of Martin life will change the way people see themselves on Earth.
- We Are Not Alone -
Currently the property of paranormal UFO posters and occasional scientists' speculation (see the Drake Equation, for example), the admonition that we are not alone in the universe would take centre stage once there was commonly accepted evidence that life once existed on Mars.
If life exists - or at least, existed once in the past - on even one other planet in our solar system, that would be evidence that it is relatively abundant in the universe. The question then would become, not whether life exists elsewhere, but how often life occurs elsewhere.
Of course, it is important to remember that the mere fact of some sort of life existing on Mars does not necessarily mean that in a few hundred years we will take our place within a galaxy rich in alien civilizations, the sort of utopian future imagined in pulp science fiction like Star Trek.
Indeed, intelligent life could still be extremely rare - not least because it tends to destroy itself, through nuclear wars, resource depletion, pollution, and so on.
Or, perhaps, it is quite common and we simply lack the means to detect it. In any case, we are likely to find only evidence of micro-organisms (on Earth, bacteria) on Mars, and it may have got there the same way it reached Earth - complex organic compounds and amino acids deposited by crashing comets.
All of this is to say that discovering new evidence of life on Mars in many ways raises more questions than it answers. Nevertheless, if there was life on Mars in the past, then one thing can be said for certain: Earth is not the only place in the universe where life has existed.
- Our Place in the Sun -
This will require a dramatic rethinking of our place in the universe. Traditional cosmologies - religious ones in particular, but also many secular ones - tend to begin from the assumption that human beings are the sole rational conscious actors in an otherwise largely unthinking, mechanistic universe. (Some exceptions are made for chimpanzees and cetaceans.)
Religious ones often add that the world as we know it was tailor-made for the support and sustenance of human life.
However, if life exists on other worlds as well, then we clearly were not as unique as we supposed. We will need to develop new ways of thinking about ourselves and our place in the universe.
This does not necessarily mean the sort of improvised attempts at melding astrobiology and religious doctrine that we get when, for example, the director of the Vatican Observatory begins to speculate about "extraterrestrial brothers" in official Roman Catholic publications.
In addition, it doesn't necessarily mean that people will grow more mature. On the one hand, many believe that realizing we are part of a community of intelligent civilizations will make us more respectful, perhaps more peaceful. But that should have happened anyway.
Consider the fact that the alternative is that we are alone in the universe - and if so, human life is incredibly precious indeed. Either way, should not the petty political and social conflicts of the nations of Earth pale in comparison to the vastness of space, of the wonders that lie in wait in our galaxy alone?
Nevertheless, new evidence of life on other worlds will necessarily mean some changes to the way people see themselves on Earth - and that evidence is most likely to come first from our nearest neighbour, Mars.
Conclusive proof that life once existed elsewhere will mean that we must recognize ourselves as only one form of life. And that will mean considering the possibility not just that life exists elsewhere in the solar system, but that intelligent life exists elsewhere in the galaxy.
If that's the case, what would it mean for the history of humanity? Could we try and contact those other intelligent species? Should we?
So far, those questions have all been asked, speculatively, by groups like the Search for Extraterrestrial Intelligence (SETI). However, the actual discovery of evidence of life on Mars would turn that speculation into the foundation for some much more concrete and pressing philosophical questions about the nature of humanity and our place in the universe.