When packing for a trip towards another planet, there are some things, such as microorganisms, that you do not want to include in your ‘luggage’. For example, what if extraterrestial life is finally detected on Mars, and scientists realise afterwards that such life is actually terrestrial? Fortunately, there are strict international rules to avoid the contamination of Solar System bodies with biological material from Earth. Landers, for example, may present a special danger to the objects they set down on. The European Space Agency (ESA) is well aware of this.