Could the 9th planet be virtual?

Question

Astronomers recently claim that there is evidence for a 9th planet. As far as I understood it, this is mainly based on coinciding orbital parameters of a few Kuiper belt objects.

Could the 9th planet be a virtual planet? I mean this in the sense that we see the gravitational influence of a multi-body system. Could the 9th planet simply be the barycenter of the Kuiper belt and its apparent orbit some form of precession?

Apart from the question, if this was a possible or likely scenario, how could we distinguish a "real" 9th planet from a virtual one, except by the obvious answer if we can observe it directly?

Forgive me, if this is a stupid or trivial question or if this was answered before. I am not a professional astronomer, yet I have a physics/engineering background. I did a quick internet search to answer this question but I simply may have used the wrong terms or sources.

Answer 1

The ninth planet can absolutely be a "virtual", in the way you describe it, meaning observed data indicating the gravitational influence by an object is not actually caused by such an object.

A simple visualisation of this is the case of a two-body system, where we observe two objects orbiting a common barycentre. From the observed data, one can get the impression that there is an object in the barycentre, pulling both of your observed objects against it.¹

However, a barycentric way to explain the observations gets less likely as you add more bodies. Be aware that the current indications of "planet 9" is based on a mere correlation of some not-so-accurate data, from a small sample size, heavily biased by observation constraints.

how could we distinguish a "real" 9th planet from a virtual one, except by the obvious answer if we can observe it directly?

That is only by its gravitational influence alone.

As a rule of thumb, incomplete and inaccurate data always imply the risk of causing virtual objects.

It should also be noted too that observations in the Kuiper belt generally can not yield how a orbit changes, due to the extremely long revolution times. observing "Interactions" are actually mostly about tracing an orbit back from its current state vectors, to find probable interaction events in the past. That is literary to ask for data artefacts and virtual objects.

¹Before anyone objects about how easy it is to falsify that: Yes it is easy to determine that there can not actually be an object there, based purely on observing the two bodies. But, that requires 1. accurate data about the motion of the two objects, and 2. their mass. Our current data about the Kuiper belt fails to give good enough data on both points.

Answer 2

That's an interesting way to put it. Indeed, since bodies spend most of their time at the slow end of an eccentric orbit, the extended lobes will attract each other, torquing the orbits into a birdsnest shape.

See this presentation by Dr. Madigan. I'm really disappointed that the more scientifically literate press (like SciAm) doesn't cover this idea, but hypes the large distant bodies idea.

(See slide at 15:58 in the video. But, it's the explaination up to that point that describes the mechanism.)

In short, the particular clustering of orbit shapes and orientations can be explained through self-interaction of the long-term averages of the bodies' orbits: the apahelion acts as a "virtual object", as you put it, and attract each other.