One of the most exciting features of astronomy today is the search for exoplanets offering life conditions suitable for life (see http://www.space.com/159-strangest-alien-planets.html). Things are far less simple than they may look at first sight. Being in HZ-range (the so-called habitable zone) is what we could define a necessary but by no means sufficient condition for sustaining life (without considering that even its delimitation changes over time. (See: http://www.spacedaily.com/reports/Habitable_zones_around_stars_ten_times_wider_than_we_thought_999.html). There are many other parameters that need to be taken into account when assessing the possibility of an alien presence, and when I say life, I don’t hint at intelligent life: even an amoeba qualifies here. One thing that has always greatly disturbed me when reading sci-fi is spotting some obvious mistakes when describing alien-life scenarios. An example: no name dropping here, but imagine somebody illustrating a giant planet with intelligent, human-like life happily sauntering on its surface. First consideration: how the hell they do that? If it is a giant, chances are that is a gaseous one like Jupiter or Saturn. No solid ground for hopping onto. Second, if by any chance (first suspension of disbelief) planet is fit-for-walk, what is the likelihood that the humanoid can actually move instead of being grounded flat on it by its gravity? It may or may be not. More parameters needs to be taken into account to answer, planet’s mass and radius for sure, which rarely happens.
Epsilon Eridani b, the closest to Earth with only 10.5 light years of distance.
(Credit: NASA, ESA)
Analyses of this kind can go on and on, in terms of noticing all sort of incongruence when not of blatant mistakes. Now, what separates SF from fantasy (which I appreciate, but on a different ground) is the presence of that sci in the acronym. Give me winged dragons breathing flames and all-powerful micro-organisms with psycho-powers: I can accept it. But as a scientist, and (even worse) a mathematician, I am open to the impossible, not to the unlikely.