I was listening to a Neil Degrasse Tyson interview and he believes the criteria for life is far more broad than we believe it to be. His main criteria were;
- Water
- some sort of energy source
- entropy (there have to be larger concentrations of energy and heat in certain areas while lesser in others to create an ecosystem)
His basis for this was that life is far more resilient than we give it credit for. For instance, we've found flourishing ecosystems literally miles underwater in pressures that normal life simply couldn't withstand.
- This shows us that life can handle greater or lesser planet sizes (broadening the amount of potential planets for life).
- It also shows us that the proximity from the sun may not matter as long as there is another source of energy (thermal). So life can exist in deep seas or potentially underground despite how uninhabitable the surface may be. (Broadening the potential planets even more).
He then went on to point out the existence of rogue planets, which are planets that have escaped the gravity of a star and are hurled into space. It's believed that there may be as many, if not more rogue planets in the universe than planets orbiting Sun's.
By most scientists criteria, these rogue planets couldn't possibly sustain life. However, Tyson argues that they still could in deeper oceans or underground as long as there is still an abundant amount of thermal energy. (Which again, adds even more potential planets).
To me, the possibility of life on other planets is so high that it's a virtual impossibility that we are the only life forms. I have no idea how or when we will find it, but it's out there somewhere.
