Parsing Whether Astronomers Discovered Exo-Life
Eight years ago I wrote on Medium that the discovery of extraterrestrial life will
likely will happen not with a big splash of absolute proof, but rather with a ripple from an observation amounting to “wow, that’s odd.” Then the observation will require confirmation from additional sources . . . Still, the observation is likely to be sufficiently ambiguous in nature that more mundane possibilities must be ruled out, after all, extraordinary conclusions require extraordinary evidence . . .
All of that will take time. The process to prove an ambiguous observation is truly alien life will evolve over an indeterminate time as more data takes scientists from the conclusion that it might conceivably could be evidence of alien life, to believing the data suggests there is a credible chance it evidences alien life, to more studies showing it probably is alien life, until scientists finally get to where they can state with confidence it almost certainly is alien life. It will likely happen this way because that is how science, at least good science, works in real life.
Two years ago the “wow, that’s odd” moment occurred regarding an extrasolar planet known as K2–18b with a tentative observation from the new James Webb Space Telescope (JWST) of sulfur based compound known as dimethyl sulfide (DMS). DMS had previously been identified as a compound whose observation on other planets would strongly suggest life because, at least on Earth, there is no other way it can be made. However, the observation two years ago was not regarded as verified, scientists were not sure DMS was really detected and many were skeptical based on other observations of the planet.
Reproducibility of results is the acid test of science. Scientists retrained the sensors of JWST on K2–18b, using a different and more sensitive instrument. The new data is in, and it is exciting, doing much to remove the ambiguous nature of the prior observation.
The new measurements found DMS (and/or related molecules) abundantly in the atmosphere and with a 99.7% certainty. This compelling finding is being described as the strongest evidence to date of extrasolar life. The observations are consistent with the notion that K2–18b is an ocean world teaming with microbial, plankton like life.
Scientists are not yet satisfied with that 99.7% observation and now seek additional measurements of the planet to raise that to at least 99.99994%. Nobody wants to claim to have found ET without really being sure. Scientists must complete two more steps before concluding this proves life.
1. Rule out chance in the observations as described above.
2. Establish that the presence of these compounds cannot be explained by unforeseen chemical processes on the planet.
The first of those has already effectively been satisfied, in my view. While scientists seek improvement on the 99.7% probability, and will work to cross their statistical t’s, odds already strongly favor that the observations are not a reflection of chance. It is very unlikely further observations will undo this result.
Number 2 is more challenging as it requires proof of a negative. How can scientists know when they can rule out the possibility that some process, unrelated to life, that we don’t understand, is producing the compounds observed?
Complicating the effort is that K2–18b is not a very Earth like planet at all, with no close analog in our solar system. With roughly 8.5 times the mass of Earth it’s gravity would be crushing for us. The closest planet in our solar system in size is Neptune, which has about twice K2–12b’s mass. However, unlike Neptune, K2–18b is so close to its white dwarf star to get about 120% of the radiation from it that Earth does. It may fit within the category of a “Hycean Planet” which scientists had previously determined might be good candidates for life. Still, figuring out whether the chemistry for such a planet might allow for non-biologic production of DMS could be daunting.
Scientists will be scrambling now to identify such potential processes. What if they can’t find any? That would be more evidence that life exists off our own world.
K2–12b is only 124 light years away, practically our stellar backyard. If it does have life its proximity will strongly suggest that life is common in the universe, and it will show that life can occur on planets very different from our own.
One thing for sure, K2–12b deserves a name. I’m already tired of calling it that.
