In a new paper published in Nature, outgoing NASA Chief Scientist Jim Green and co-authors call for a framework for scientists to use in reporting evidence of extraterrestrial life. They suggest that a high level of confidence in such a claim requires that there first be a community-level dialogue among scientists. Otherwise, they say, there is danger, given the complex and diverse subject matter, that the findings will be misunderstood and sensationalized.
The authors propose a Confidence of Life Detection (CoLD) scale, consisting of seven benchmarks, to quantify how much confidence the general public should have that extraterrestrial life has indeed been found. To reach Level 4, for example, all known non-biological sources would have to be shown to be implausible in the environment where the signal was detected.
Green compares the CoLD proposal to the Torino scale used to assess the danger from an asteroid or cometary impact. For that scale, statistics on the probability of impact are combined with the expected effects of that impact to come up with a single threat value.
Although I think the idea behind the CoLD framework is certainly conceptually helpful, it isn’t clear how practical the approach really is. Only two parameters go into calculating the Torino scale, while life detection is much more complex, with many more parameters going into the equation.
The authors emphasize that their proposal is “offered to demonstrate intent, proof of concept and utility, and not a prescription.” But it’s an open secret that many within NASA were unhappy with how the claimed detection of possible signs of life in the atmosphere of Venus was reported last year. Many scientists and reporters got excited at the news, including myself, and some may have gotten carried away. But is this really so bad? Do we want to suffocate that excitement?
In my view, the scientists who reported the phospine detection phrased their conclusions very carefully. They checked thoroughly for non-biological sources of phosphine and found none, even in follow-up studies. So they concluded that the biological explanation should be considered as one possible option. Naturally, other scientists disagree, but that’s the scientific process. And eventually, if we’re patient long enough, we’ll know whether the claim can be verified or whether it has to be refuted. One positive outcome of the phosphine debate is that it has kindled a new interest in Venus: Three new missions have been approved to visit the planet, two from NASA and one from the European Space Agency.
The result will be that we gain valuable new insights about the planet—whether it was once habitable, and whether life of any kind could possibly adapt to the harsh conditions in the sulfurous Venusian clouds. In some ways the phosphine debate is similar to the controversy surrounding a 1996 claim of fossils in a Martian meteorite. While that report didn’t hold up to scrutiny, the original paper by David McKay was instrumental in the creation of the NASA Astrobiology Institute, probably the single most important step to establishing this young field of science and giving it credibility.
While I think Green and his colleagues make many good points, I’m concerned that their proposal could lead—unintentionally—to censoring scientists who might come forward with ambiguous but nonetheless exciting evidence of extraterrestrial life.