47 Ursae Majoris as imagined by Debivort. The proposed "Planet Nine" might look similar to this.What should we make of the claim that there is an unknown entity lurking on the fringes -- an entity that would not overthrow everything we think we know about our place in the universe but would give it a tweak -- when the evidence in favor of the entity falls short of what is normally demanded for such things, but is sufficient to be suggestive? This is an inherently "fuzzy" question, because ideas like "sufficient evidence" and "suggestive evidence" are at least partially subjective. In such a case, it is important to have some estimate of the background noise of false positive observations; how likely is that the suggestive evidence is something other than a collection of false positives? The answer to that question will determine how much confidence we have that the claim will eventually be verified, and our degree of confidence will strongly influence how much money, time, and effort we devote to the search. However, in the absence of better evidence (or a better analysis of the existing evidence), it would be foolish to commit to either the proposed entity being real or to it being unreal.
From the title of this post and from the very vague language I have used, it is clear that I think it is worthwhile to compare and contrast the claims that there is an indigenous North American ape and that there is a large planet in our solar system beyond the orbit of Neptune. The similarities are obvious. The standard proof needed to name a new species is possession of a type specimen -- a body that makes it clear that the new species is both real and distinct from other named species. There is no type specimen for a Bigfoot, only a collection of sightings, photographs, and footprints -- and it is certain that most of these are either frauds or cases of mistaken identity. Likewise, the standard proof needed to name a new astronomical body is a series of direct observations from which the orbit can be determined in some detail. There are no direct observations of "Planet Nine", only observations of small objects beyond Neptune that may have been perturbed by the gravity of the hypothetical object. Yet the reception by the scientific community of the two proposed is very different. Why?
I can only come up with three good reasons to treat the astronomical case differently than the biological case.
- The first is that astronomy is much, much, much more mathematical, so that it is possible to calculate (subject to a handful of reasonable assumptions) what size and type of telescope would be able to see the hypothetical planet. This means they are able to give an explanation for why Planet Nine has not yet been seen. In fact, the team that proposed Planet Nine has even attempted to calculate the odds that the orbital irregularities of bodies like Sedna are due to something else, though I suspect they underestimate those odds. In contrast, as far as I know there has been no serious attempt to quantify how many "Bigfoot sightings" we should expect each year if Bigfoot is not real and all the "sightings" are mistakes or hoaxes.
- Related to the first point, the hypothesis of Planet Nine is falsifiable. If sufficiently powerful telescopes exhaustively search the area of the sky indicated but fail to find Planet Nine, astronomers will just shrug their shoulders and move on. Belief in Bigfoot, on the other hand, seems to be perpetually content with fuzzy photos, dubious footprints, and the accounts of alleged witnesses.
- Finally, the evidence for Planet Nine is objective, available to everyone, and impossible to fake. The interpretation may or may not be correct, and how convincing it is in its current form is a somewhat subjective question, but anyone with a large enough telescope can confirm the raw data. This is not really true for Bigfoot evidence. Eyewitness accounts are entirely subjective, and the credibility of footprints depends on how they were discovered -- a process that cannot be independently repeated.
These are important differences, and all told, I consider the Planet Nine hypothesis both to be better science and to be proven correct. Regardless, it is important to be prepared for the possibility that either hypothesis may be false and also for the possibility that either hypothesis may be true.