未知

qì jīn tā de xià luò dōu quán rán wèi zhī

迄今他的下落都全然未知。

His whereabouts have been utterly unknown so far.

zhè xiē yǔ háng yuán kāi shǐ le duì wèi zhī shì jiè de tàn suǒ zhī lǚ

这些宇航员开始了对未知世界的探索之旅。

The astronauts began their journey into the unknown.