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How can microscopes help detect microorganisms on another world?

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Planet TOI 700e — extraterrestrial life An illustration of the Earth-size planet TOI 700e orbiting within the habitable zone of its star. The habitable zone is the area around a star where liquid water, and thus possibly life, can survive on a planet's surface. Its Earth-size sibling, TOI 700d, can be seen in the distance.

In the field of astrobiology, microscopes are considered potentially optimal tools for detecting life on other worlds because they can identify microorganisms, which are far more abundant than larger life-forms in many ecosystems.1

When conducting in situ studies—where a spacecraft lands on a planet to perform experiments—a television camera coupled to an optical or electron microscope could be used to observe samples of soil or water for signs of life. This approach mirrors the historical success of Antonie van Leeuwenhoek, who identified living "animalcules" in water using early microscopy.1

However, utilizing these instruments for extraterrestrial exploration presents significant technical challenges, particularly regarding the acquisition and preparation of samples for remote examination. Furthermore, researchers must be extremely cautious to avoid contamination, as any microorganisms carried from Earth could be mistakenly identified as extraterrestrial life. Because no single "life detector" is foolproof, scientists recommend using an array of both general and specific instruments to confirm the presence of life.1