sometimes its funny how these scientists are trying to find deviance of life in other planets...
the success for the search is always depends on what to look for.. If you are looking for the images of Spider Man or Barak Obama in the mars's surface, chances are less to get evidence for life in outer space!!!!
the most common method they follow is to search for certain organic compounds...
But still I see a weakness in this as well, since they are searching for the life that can be found and originated in planet earth..
If there is a living being in the planet neptune, we cant expect them to be as us, since the conditions in the neptune is very different.