Finding extraterrestrial life isn’t necessarily as simple as looking for it with our eyes. A lifeform might be too small to see, or too far away, or too different than what we expect to find. In addition to direct observation, we can also infer (deduce) the presence of life by looking at traces (clues) that a living thing leaves behind.

Detecting waste products

• If we suspect, for example, that a lifeform undergoes respiration, we can assume that it would produce carbon dioxide (CO₂).
• We should thus be on the lookout for the presence of such waste products.