Aliens are too lazy to explore Earth.
Aliens don't feel the need to come to Earth
A NASA expert has suggested that humans are yet to encounter extraterrestrial life as the little green men have already achieved a "sustainable population" on their own planet.
Scientists reached the conclusion after tests searching for alien solar panels on a nearby exoplanet with a next-generation space telescope failed to find any evidence.
The US space agency added that the aliens could have used "relatively modest" amounts of energy to enjoy a "very high standard of living".
Ravi Kopparapu, of NASA's Goddard Space Flight Center in Maryland, said: "The implication is that civilisations may not feel compelled to expand energy all over the galaxy because they may achieve sustainable population and energy-usage levels even if they choose a very high standard of living.
"They may expand within their own solar system, or even within nearby star systems, but galaxy-spanning civilisations may not exist."