Aliens have not contacted Earth as yet because they probably live in underwater civilizations. That's a new theory presented by planetary scientist Alan Stern, from the Southwest Research Institute in Boulder, Colorado. He's concluded that our alien neighbors live in subsurface oceans covered by layers of ice which explains why communications from them haven't reached our planet as yet.
Many of the planets and moons in our solar system have oceans, Science Mag notes. Large bodies of water can be found on many of Neptune's moons, as well those orbiting Jupiter, Saturn, and Pluto. Each of these planets have icy crusts which develop into frozen mountains and canyons on the surface.
But at the lower levels, these large ice-rock formations melt and form oceans. Hydrothermal vents in these oceans could supply the environment with nutrients, sparking the development of vibrant ecosystems. These ecosystems are protected from the rest of the atmosphere by a thick icy shell which could make them more "productive" than Earth's ocean environments.
Stern suggests that intelligent alien creatures in these ecosystems would have a different perspective of "space" than humans do. Space for them may be the frontier beyond the ice cap that keeps their world separate from the rest of the planet.
This new theory from Stern could be the solution to "The Fermi Paradox."