VOA慢速英语:Hawking, Zuckerberg to Search for Life in the Universe

alien – n. a creature from somewhere other than Earth

ambitious – adj. something that will take a lot of time and effort and is difficult to achieve

gram-scale wafer – n.  a small object that weighs about a gram

photon thrusters – n. a device that helps move a spacecraft forward

transcend – v. going beyond or rising above normal limits

void – adj. empty

on the contrary – phrase. the opposite

beam -n.  a line of light

postage stamp – n. a small square on a letter for payment to mail

commit – v. to say you will definitely do something

cosmos – n. the system that is the universe

timeline - n. a schedule of events