In seeking to find life beyond Earth, scientists must first understand which signs would be the most convincing evidence.
For the past 20 years, NASA spacecraft have been searching for potentially suitable conditions for living in the solar system and beyond. The device on Mars found evidence that the planet had lakes and streams, once protected by a dense atmospheric layer. On Saturn's moon Enceladus, the Cassini ship spotted water jets released from the ice layer. The future European mission of Clipper can conduct similar research on the satellite of Jupiter in Europe, where they noticed even more jets. Even outside our system there are thousands of alien worlds with superficial oceans.
The next step in exploring the alien environment will be to find out whether they are really suitable for life, and only then should we start the search. Unfortunately, there is no simple method for detecting life. The camera fails to capture a growing marker of bacteria on Martian rock or under Enceladus ice, so you have to use a set of tools and various data to search for biomarkers.
But what are the signs of life? To understand this, NASA scientists created the “Life Detection Ladder”, where each step is a key attribute of life.
The staircase holds 15 features that scientists define as indicators of life. She also describes exactly how researchers will be able to measure these characteristics and understand whether they are really evidence of life. All life we know needs complex organic molecules and uses amino acids - two features in the stairs. But their discovery does not prove the fact that they are produced by living organisms. For example, many chemical reactions on the planet create amino acids and other organic molecules.
Indicators may be target molecules that are found in unique proportions compared to expected levels in the environment. Other biosignals include pigments, signs of metabolism (for example, waste heat) or even signs of Darwin’s evolution.
Next you need to understand: can scientists measure these biosignals remotely and in place? The essence lies not only in the efficiency of the instrument, but also in eliminating the factor of contamination of samples by molecules brought from the Earth. Researchers must also consider the environmental context. How fragile is the sample? Can analysis destroy it? Does the medium chemically affect the sample?
The ladder gives answers to every bio-censorship, based on the experience gained in the search for Martian life or in ancient terrestrial rocks in the most extreme conditions. It turned out that lighter measurements (lower stages) are more difficult to interpret than higher ones. The authors remind that their “Ladder” is a mobile tool and may change / be supplemented with the receipt of new data.