NASA scientist suggests reason we haven't found aliens yet – and it's pretty simple
![NASA scientist suggests reason we haven't found aliens yet –
and it's pretty simple](https://i2-prod.dailystar.co.uk/incoming/article33417860.ece/ALTERNATES/s615/1_Grey-Aliens-and-their-flying-saucer-visiting-Earth.jpg)
Humans haven't found any little green men yet because they might just be happy where they are, says Ravi Kopparapu, of Nasa’s Goddard Space Flight Center in Maryland, US