2.1 Biological contamination

In the context of planetary protection, ‘biological contamination’ is not referring to humans in space – it is microscopic life – microbes.

Watch Video 2 that revisits some of the ideas you have already met about the definition of life. After watching the video, answer the questions that follow.

Microbes include various, diverse groups of organisms. Bacteria (singular: bacterium) are the most common microbe. In fact, bacteria are probably the most abundant group of organism on the Earth; almost all surfaces which have not been specially sterilised harbour bacteria. Archaea (singular: archaeon) are a separate domain of life, are also single celled and have been found in many environments including those with extreme environmental conditions, such as hot springs in volcanic areas. 

While bacteria and archaea are prokaryotes, there are also microbes that are eukaryotes. Microbial eukaryotes include Fungi, such as yeast, and Algae, such as those which form the powdery green coating on the shady side of tree trunks. The term microbe also includes Viruses, which you considered in Activity 2.

Some microbes perform roles that are beneficial to humanity, including supporting the production of food and medicines (e.g., Saccharomyces cerevisiae and brewing). Other microbes can be harmful, causing infections or disease in animals and plants (e.g., Escherichia coli and food poisoning). However, most microbes have no direct effect on humanity, positive or negative.

Since microbes are everywhere – including on the skin, breath and clothes of astronauts, on and inside spacecraft, within the facilities in which spacecraft are built and tested, and even within the fuel tanks that might propel the missions – they present a challenge to planetary protection. Terrestrial microbes can also tolerate a much wider range of environmental conditions than humans can, which means they could survive in planetary environments beyond Earth if we were to take them there.