Recent evidence suggests microbial life may have been present on Mars, deep in that planet’s past. Some microbes have been exposed to space and survived, suggesting they are tough enough to endure incredibly harsh conditions. If life is something that originates easily, then it is probably only a matter of time before we find evidence of living, or extinct, alien microbes. But, once all the hype associated with this first evidence of life beyond Earth has died down, will microscopic aliens really excite us?
The search for life beyond Earth has so far been unfruitful. However, the more we look at the solar system around us, the more it looks like a wide range of nooks and crannies could be suitable homes for one form of Earthly microbe, or another. The high clouds of Venus, the soils of Mars and the sub-surface oceans of Europa are just some of the list of possible microbial habitats beyond Earth. Microbiologists generally seem to find microbes incredibly exciting and many non-microbiologist astrobiologists (including me) share this opinion, and with good reason. Microbes allow us to class many more environments as “habitable”, both nearby in the solar system and on planets around other stars. They are known to tolerate temperature extremes above 100°C and below 0°C. They can survive dosages of radiation that would be lethal to animals. They can cope with high pressures, extreme salinity and, in some cases, even exposure to space. If they were animals, they would certainly look weird and wonderful; unimaginable exotic armoured vehicles of the natural world. Unfortunately, they almost all look like little squiggly line or dots (one notable exception being the tardigrade, or water bear - although this is technically a micro-animal). Are people really going to get excited about finding tiny alien dots and off-world squiggly lines?
In some ways it can be argued that we probably should… Life on Earth started out as single-celled microbes and stayed that way for over 2 billion years, when multicellular life finally began to make an appearance. So we know that microbes at least contain the potential to turn into things like trees, dinosaurs and even something clever enough to pick up a stick and dig for food. Finding microbes living somewhere else (or in several somewhere elses) could give us an idea of how common life is in the universe and it could be the prelude to discovering more - an exciting step in the search for life and towards an understanding of our place in the universe. However, in reality, we might end up viewing the existence of alien microbes with no greater sense of surprise than we hold for the existence of grass and trees on the other side of the ocean to us. So many environments in the solar system could support microbes, that a general expectation is growing that we will find them somewhere.
There is plenty of evidence suggesting that Mars was once warmer and wetter in its past. Ancient microbial life could happily have made a home there. A recent analysis of images from the Curiosity rover suggest that we may potentially have found evidence that microbes were indeed present on the red planet once-upon-a-time. An important and interesting scientific finding, if this turns out to be true. But would it be a discovery that would pique the interest of readers of a future school biology textbook? Readers who have perhaps grown up in a world where this discovery occurred before they were born… Perhaps this textbook would also contain a section on deep-sea hydrothermal vents that includes a paragraph, or two, on Europan microbes living in the ocean beneath Europa's icy surface.
All these topics are obviously very scientifically exciting, but would interested non-scientists (a very large and varied group of people, given the huge public interest in the search for extraterrestrial life) still be left wanting exotic looking plants, strange creatures and even the clichéd little green men? Perhaps the search itself is more exciting than its conclusions, however weird and wonderful they may be. The existence of planets orbiting other stars was once a mystery, but now we know of thousands of them and, unless a planet that closely resembles Earth turns up, most people barely notice when that number hurtles up in leaps and bounds. Are we always going to be excited about life beyond Earth, or, if and when the unknown becomes known, are we going to lose interest? Time will tell.