spaceSpace and Physics

NASA Scientists Say We Need A Plan For When We Discover Alien Life


Dr. Alfredo Carpineti

Senior Staff Writer & Space Correspondent

clockOct 29 2021, 16:28 UTC
Image Credit: Dotted Yeti/

Recognizing alien life might not be as straightforward as we have come to imagine it. Image Credit: Dotted Yeti/

The question if earthlings are alone in the universe is one that weighs on our minds. If we're not, then what will other life be like? Will it be very simple or advanced? Will we even be able to recognize it as it might be very different from us? For all these reasons, NASA scientists are proposing the world agrees on an approach to how we announce any future discovery that may or may not be extraterrestrial life to minimize any misunderstandings.

First, it is important to remember that we shouldn’t bank on finding something that is unequivocally life. It may not appear in the form of little green men or ET or even Gonzo. It's a lot more likely that the signatures of life we might observe would give an exciting but far-from-certain result. Any evidence will have to be checked and checked and double-checked again, which can take time. For this reason, having a framework to deal with how to convey such a discovery is important to prevent any results from being taken to mean more than they are.


In a perspective piece published in Nature, NASA researchers discuss the need for a methodical approach, and how it will be beneficial to have something in place before any credible discoveries come to light. "Our generation could realistically be the one to discover evidence of life beyond Earth," the piece begins. "With this privileged potential comes responsibility."

They have even suggested a possible scale called CoLD, or the Confidence of Life Detection scale. It has seven levels, to make sure what we are seeing is undeniably life. Level 1 is the detection of a signal that could be biological. The next step is ruling out any human or earthly contamination. The next two levels focus on making sure it’s a biological event and not a chemical one unrelated to life. Getting to level 3 requires demonstrating that a biological source can produce signals and level four requires the exclusion of all non-biological sources in that environment.   

Level 5 is achieved when an additional independent signal from biology is detected. Level 6 is reached when all alternative hypotheses announced after the first detection are excluded. And finally, level 7 is the independent confirmation of more biological behaviors.

Applying the CoLD scale to famous examples actually puts them in better context. The notorious 4.5-billion-year old Martian meteorite ALH84001, which might have evidence of ancient life processes in it, reaches a maximum of level 3.


The question “Is it evidence of life? Yes or no?” is not the right kind of question anymore, the researchers argue. Such an important topic needs more nuance.

"Realizing this potential requires a community-level dialogue among scientists, technologists and the media to agree on objective standards of evidence for life and best practices for communicating that evidence," the authors write. 

"Doing so before life-detection results are reported, rather than in response to a specific finding, will enable a more dispassionate, objective, and broad-reaching treatment of the subject and ensure that its packaging supports clear understanding by the public at large. The purpose of this Perspective is to call for such dialogue and propose a draft framework and set of considerations to seed the discussion."

The CoLD scale might not be the one the global scientific community settles on but a framework to agree what would count as evidence of life elsewhere in the universe and how best to communicate it would certainly benefit the discussion.

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