1.They are thought to travel to Earth from other galaxies and extragalactic sources.

认为是从其星系和星系外的来源来到地球的。

2.That's because scientists don't know for sure if they've identified an extragalactic exoplanet.

这是因为科学家不确定是否发现了一系外的行星。

3.The researchers say more data will be needed to confirm the observation as an actual " extragalactic exoplanet" .

研究人员说，还需要更多的数据来证实这是一真正的" 星系外系外行星" 。