There was once more than enough water on Mars to support extraterrestrial life. There were lakes, streams and networks of underground water of drinking quality, and it is possible that these existed for millions of years. There is also evidence of nitrogen and carbon in the rocks and stones on Mars. These are, of course, the chemicals needed for any type of life.
We know all this due to the work done on the red planet by the three now world-renowned exploration rovers. Spirit and Opportunity were sent to Mars in 2004 primarily to search for evidence of extraterrestrial life. Spirit continued working until March 2010, and Opportunity is still going. Then in 2012, Curiosity, a much smaller Mars Exploration Rover (MER) was landed at the Gale crater, which has now been revealed to be “a system of ancient environments.”
To celebrate Opportunity’s decade on Mars, Science magazine today published a special issue with five articles that describe how Mars “would have been habitable by chemoautotrophic microorganisms.” These are organisms like a protozoan or bacterium that gets nourishment from the oxidation of “inorganic chemical compounds” rather than photosynthesis. Another article talks about an even older (ancient) environment, that existed more than 3.7 billion years ago. This is also considered to be an environment that would have been “potentially habitable” at the time.
In an article introducing the special edition of Science titled Habitability, Taphonomy, and the Search for Organic Carbon on Mars, John P. Grotzinger clarifies that while the results of 10 years of research by MERs shows that “early Mars was habitable,” this does not prove that Mars was in fact ever “inhabited.” So while there is evidence that extraterrestrial life was possible on Mars billions of years ago, to be sure whether some type of life existed, scientists need to prove the fact.
In their “search for organic remnants of past life,” it was hugely useful to have a guiding paradigm, says Grotzinger. This began with an assessment of habitability that focused on whether the environment that once existed on Mars was ever able to support life. Having discovered that it was able to do so, the second assessment was whether organic remains (in the form of large organic molecules) were, or could have been preserved.
As he points out, the ultimate challenge is to uncover scientific evidence of what existed billions of years in the past. While Mars is the topic here, there was a similar challenge to prove microbial life was present on Earth billions of years ago. Charles Darwin who originated the theory of evolution, predicted that microbial life existed on Earth nearly a century before the discovery was made. The “trick,” says Grotzinger, is to find a material on Mars that has been able to preserve any possible cellular structures. And if life did exist on Mars, he says, a future mission could prove this to be so.
A future mission could do the same for Mars if life had existed there. John P. Grotzinger
One of the questions on most people’s lips is if life could have been supported on Mars, but wasn’t, what could have gone wrong?
According to Dr. Paulo de Souza who is a scientist working on NASA’s MER Program, Martian water was once like the best spring water we now find on earth. For this reason he believes that microbial life could have existed on Mars at that time. But it all changed when an enormous asteroid collided with Mars, exposing volcanic rocks and chemicals that were dissolved into the water. From being fresh and pure, it became acid, over time leaving evidence scientists have been able to analyze. Not only do they know that water was once plentiful on Mars, they can see just how the quality of that water changed over a period of time.
It is like “looking at a book of history,” says de Souza, likening it to a story where everything about Planet Earth has been recorded in minerals. While they haven’t actually found fresh water, they can see exactly where it was and when – from the minerals that have formed in the rock. This evidence also shows that whatever form of life was possible before the impact of the asteroid de Souza talks about, would not have been possible afterwards. The water would have been much too salty and acidic for even the hardiest microorganisms to survive.
So the research continues, and while we know for a fact from the NASA research that extraterrestrial life of some kind was possible on Mars, we just don’t know what kind of life was possible and whether it ever existed.