如果有外星人的话，可能长这样

To find out, Kaku interviewed experts in exobiology, a field that studies what life might be like in distant worlds with different ecosystems. Based on his research, Kaku decided that intelligent alien life would have three necessary features:

1. The aliens, like humans, would have stereo vision, which allows eyes to compare images and track distance — a necessary feature in predators, who hunt and track their prey. “In all likelihood, intelligent aliens in space will have descended from predators that hunted for their food,” Kaku writes. “This does not necessarily mean that they will be aggressive, but it does mean that their ancestors long ago might have been predators. We may be well served to be cautious.”

2. The aliens would have some form of opposable thumbs or grasping appendages, necessary for hunting prey and creating tools (which they would have to do to be sophisticated enough to make contact).

3. They would also need to have language. “In order to hand down and accumulate essential information from generation to generation, some form of language is crucial,” Kaku writes.

In addition, Kaku theorizes that many alien civilizations will exist on ice-covered moons (like Jupiter’s moon Europa or Saturn’s moon Enceladus), where life would exist completely underwater. So how would an aquatic species become truly intelligent beings?

见：

Here's what aliens probably look like

http://www.foxnews.com/science/2018/02/26/heres-what-aliens-probably-look-like.amp.html