  The orbit eccentricities of the Solar System planets are unusually low
compared to the average of known exoplanetary systems. A power law correlation
has previously been found between the multiplicity of a planetary system and
the orbital eccentricities of its components, for systems with multiplicities
above two. In this study we investigate the correlation for an expanded data
sample, by focusing on planetary systems as units (unlike previous studies that
have focused on individual planets). Our full data sample contains 1171
exoplanets, in 895 systems, and the correlation between eccentricity and
multiplicity is found to follow a clear power law for all multiplicities above
one. We discuss the correlation for several individual subsamples, and find
that all samples consistently follow the same basic trend regardless of e.g.
planet types and detection methods. We find that the eccentricities of the
Solar System fit the general trend and suggest that the Solar System might not
show uncommonly low eccentricities (as often speculated) but rather uncommonly
many planets compared to a "standard" planetary system. The only outlier from
the power law correlation is, consistently in all the samples, the one-planet
systems. It has previously been suggested that this may be due to additional
unseen exoplanets in the observed one-planet systems. Based on this assumption
and the power law correlation, we estimate that the probability of a system
having 8 planets or more is of the order of 1%, in good agreement with recent
predictions from analyses based on independent arguments.
