Something I just remembered reading about some years ago and discussing with my colleagues.
Would you believe bacteria in solid granite deep in the earth! They replicate about once every hundred or thousand years. Their biomass could be greater than what is on the surface!
Is this alien enough for you?
Here
http://nai.nasa.gov/news_stories/news_print.cfm?ID=46
and here
http://aem.asm.org/cgi/content/abstract/76/14/4788
There is far more if you google
Were these bacteria subducted eons ago by tectonic plate movements? Or did they originate there?
I will quote the line all scientists use at the end of any paper 'further work is needed'.
Why all life on earth uses the same template for DNA, RNA and proteins etc. is for one simple reason if you have a different system you cannot exploit other life for food.
Even in the eighteenth century scientists knew that there had to be enzymes that broke down all different forms of organic matter originating from life. Say that flies legs were impervious to breakdown then we would be knee deep or higher in flies legs.
Until a bacteria evolves to break down the plastics we are polluting the earth with, we will end up with plastic everywhere. It is already a major pollutant in the oceans and responsible for countless deaths of sea life.
I do agree we have no proof of any life outside our Earth. Consider though how many exoplanets did we know of twenty years ago, zero?
Opinion or hypotheses count for nothing but at least it opens the mind to look for the evidence.
Titan looks like a good place to start.
Bert