  A sample of spectroscopic binaries and a sample of single planetary systems,
both having main-sequence solar-type primary components, are selected in order
to compare their eccentricities. The positions of the objects in the
(P.(1-e^2)^(3/2), e) plane is used to determine parts in the
period-eccentricity diagram that are not affected by tidal circularization. The
original eccentricities of binaries and planets are derived and compared. They
seem to be weakly or not at all correlated with period in both samples, but two
major differences are found :(1) The tidal circularization of planetary orbits
is almost complete for periods shorter than 5 days, but it is not visible when
P.(1-e^2)^{3/2} is longer than this limit. This suggests that the
circularization occurs rapidly after the end of the migration process and is
probably simultaneous with the end of the formation of the planet. By contrast,
we confirm that the circularization of the binary orbits is a process still
progressing a long time after the formation of the systems.(2) Beyond the
circularization limit, the eccentricities of the orbits of the planets are
significantly smaller than those of binary orbits, and this discrepancy cannot
be due to a selection effect. Moreover, the eccentricities of binaries with
small mass ratios are quite similar to those of all binaries with q<0.8. This
suggests that the low eccentricities of exoplanet orbits are not a consequence
of low-mass secondaries in a universal process.
  These remarks are in favor of the idea that binaries and exoplanets are two
different classes of object from the point of view of their formation.
