There's a new theory as to why humanity is yet to receive a call from ET - and it's remarkably downbeat.
Given the apparent infinite expanse of the known universe, with its vast number of stars and planets, the numbers would point to at least some of the lumps of rock floating about in deep dark space holding the potential for life.
NASA's Kepler mission - which has been looking for a potential 'Earth 2.0' since 2009 - has already identified some 1,039 exoplanets that could harbour alien organisms. So why haven't we been visited yet?
According to Aditya Chopra and Charles Lineweaver, astrobiologists from the Australian National University, it's because most alien life that did exist is already dead.
"Early life is fragile, so we believe it rarely evolves quickly enough to survive," writes Chopra, in the recently published theory, named the 'Gaian Bottleneck'. "Most early planetary environments are unstable. To produce a habitable planet, life forms need to regulate greenhouse gases such as water and carbon dioxide to keep surface temperatures stable."
During their formation, planets such as Venus, Earth and Mars will have very similar conditions for a specific window of time. They may have an atmosphere, with an abundance of the gases necessary for the formation of basic organisms.
However, as the planets continue to mature, variables such as their position relative to the nearest star might see their environment change too rapidly for any fledgling life that has begun to emerge to keep up. In order to survive, that life will need to be directly involved in influencing the planet's atmosphere.
"The mystery of why we haven't yet found signs of aliens may have less to do with the likelihood of the origin of life or intelligence and have more to do with the rarity of the rapid emergence of biological regulation of feedback cycles on planetary surfaces," Chopra explains.
According to the Gaian Bottleneck, when we do eventually set down on a planet we think could hold life, there's a good chance we'll find masses of fossils of dead microbial life.
Here's hoping someone out there survived long enough to say hello.