In order to gain possible hints for planet formation from the current data of known extra-solar planets, the period-ratios and mass-ratios of adjacent planet pairs in multi-planet systems are determined. A moderate period-ratio-mass-ratio correlation is found to have a correlation coefficient $r=0.5779$ with 99% confidence interval (0.464, 0.672). In contrast, for non-adjacent planet pairs, the correlation coefficient is $r=0.2820$ with 99% confidence interval $(0.133,0.419)$. Our results reveal the imprint of planet-planet interactions of the adjacent planet pairs in a certain fraction of the multi-planet systems during the stage of planet formation.

为了从已知的太阳系外行星的当前数据中获得关于行星形成的可能提示，确定多行星系统中相邻行星对的周期比和质量比。发现中等周期比率-质量比率相关具有相关系数$\mathrm{[R}=0.5779$置信区间为99％（0.464，0.672）。相反，对于不相邻的行星对，相关系数为$\mathrm{[R}=0.2820$ 置信区间为99％ $（0.133，0.419）$。我们的结果揭示了在行星形成阶段，多行星系统中一定比例的相邻行星对的行星-行星相互作用的烙印。