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 can not 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 .