It's only when the first radar observations to the surface of Mercury were obtained, back in the 90s.

早在90年代，只有第一个观测水星表面的雷达获得过。

Scientists based their findings on more than 100 radar observations by the Mars express mission from 2010 to 2019.

科学家们的发现是基于2010年至2019年" 火星快车" 任务对100多个雷达进行的观测。