Abstract
Employing the data from orbital periods and masses of extra-solar planets in 166 multiple planetary systems, the period-ratio and mass-ratio of adjacent planet pairs are studied.The correlation between the period-ratio and mass-ratio is confirmed and found to have a correlation coefficientof 0.5303 with a 99% confidence interval (0.3807, 0.6528).A comparison with the distribution of synthetic samples from a Monte Carlo simulation reveals the imprint of planet-planet interactions on the formation of adjacent planet pairs in multiple planetary systems.