I cannot imagine any single discovery that would have more impact on humanity than the discovery of life outside of our solar system. There is a human-centric, Earth-centric view of life that permeates most cultural and societal thinking. Finding that there are multiple, perhaps millions of origins of life and that life is ubiquitous throughout the universe will profoundly affect every human.
We live on a microbial planet. There are one million microbial cells per cubic centimeter of water in our oceans, lakes and rivers; deep within the Earth's crust and throughout our atmosphere. We have more than 100 trillion microbes on and in each of us. The Earth's diversity of life would have seemed like science fiction to our ancestors. We have microbes that can withstand millions of Rads of ionizing radiation; such strong acid or base that it would dissolve our skin; microbes that grow in ice and microbes that grow and thrive at temperatures exceeding 100 degrees C. We have life that lives on carbon dioxide, on methane, on sulfur, or on sugar. We have sent trillions of bacteria into space over the last few billion years and we have exchanged material with Mars on a constant basis, so it would be very surprising if we do not find evidence of microbial life in our solar system, particularly on Mars.
The recent discoveries by Dimitar Sasselov and colleagues of numerous Earth and super-Earth-like planets outside our solar system, including water worlds, greatly increases the probability of finding life. Sasselov estimates approximately 100,000 Earth and super-Earths within our own galaxy. The universe is young so wherever we find microbial life there will be intelligent life in the future.
Expanding our scientific reach further into the skies will change us forever.