As an astrobiologist, I work on a variety of topics, including determining which planetary bodies are most likely to be habitable and establishing how we would go about detecting life if it is there. Often what my work boils down to is subjecting microbes to harsh conditions to see if any of them can survive. In other words, I am constantly coming up with new and creative ways to torture and kill them.
What makes my job really interesting is the fact that not all microbes are the same! Some are really good at surviving under extreme heat, others in high concentrations of salt, some can even survive the vacuum of space. This means that not all microbes are made equal, that they can differ widely in physiological characteristics. Which is wonderful but also presents some challenges when trying to determine the limits of life or where is the best place to look for life.
Let’s take for example looking for life on Enceladus. Enceladus is a moon of Saturn with an ocean covered by thin ice. There are cracks in the ice where water is being ejected into the vacuum of space. When thinking about a life detection mission to sample the plumes of Enceladus you have to think about what types of life you might find there and then how does the process of being ejected into space affect them.
There is a diverse array of organisms that could make a living on Enceladus. For example, methanogens might be able to harness the energy flux present on Enceladus. Or we might want to look at Nautilia profundicola, an anaerobic nitrate-reducing bacterium from an active seafloor vent. Or maybe a better model organism would be Colwellia psychrerythraea, a heterotrophic marine bacterium ubiquitous in cold marine ecosystems. And the list goes on.
But you can’t just look at what types of organisms might live in a specific environment, you also have to look at how the environment might affect your ability to look for signs of life. What’s the effects of the plume environment on the microbial cells? Does it destroy them? It is important to understand how the process of being ejected into the vacuum of space would impact such life in order to design missions and choose the best instruments for detecting it.
As you might be starting to imagine, there are endless ways to subject different microbes to all kinds of horrific ends. Welcome to a small part of the Astrobiology world!
Images of microbes (left) under atmospheric pressure and (right) after being injected into vacuum. Cells were stained with a fluorescence dye to show the impact on cell membranes. (Bywaters et al. 2020)