  This paper assesses if the Planet 9 hypothesis, the existence of a ninth
planet, is consistent with the planetary hypothesis, the synchronization of
sunspot emergence to solar inertial motion (SIM) induced by the planets. We
show that SIM would be profoundly affected if Planet 9 exists and that the
hypothesized effect of SIM on sunspot emergence would be radically different
from the effect of SIM due to the existing eight planets. We compare the
spectral and time variation of Sun to barycentre distance, RB, calculated for
both the eight and nine planet systems, with variation of sunspot number (SSN).
Including Planet 9 improves spectral correlation and time coherence between RB
and SSN in the decadal, centennial and millennial time range. Additionally, as
the variation of RB is sensitive to Planet 9 parameters, longitude and period,
it is possible to tune both parameters to SSN variation and obtain new
estimates of the Planet 9 parameters independent of astronomical observations.
We develop a mechanism for the influence of SIM on SSN that provides an
explanation of the consistency between SIM, calculated with Planet nine, and
records of reconstructed SSN.
