Do some topics make something ‘de-facto’ sci-fi?
For example is any story that involves time travel by default considered sci-fi? Other topics that might fit this question extra-planetary space travel, aliens, parallel universes, ect.
I'd say all those automatically count as scifi (well... mostly). From wikipedia, the definition of scifi is
Science fiction is a genre of fiction dealing with imaginary but more or less plausible (or at least non-supernatural) content such as future settings, futuristic science and technology, space travel, aliens, and paranormal abilities. Exploring the consequences of scientific innovations is one purpose of science fiction, making it a "literature of ideas".
Science fiction is largely based on writing rationally about alternative possible worlds or futures. It is similar to, but differs from fantasy in that, within the context of the story, its imaginary elements are largely possible within scientifically established or scientifically postulated laws of nature (though some elements in a story might still be pure imaginative speculation).
Generally, science fiction is taking established facts of science and adding a "what if" to it, either in the form of "what if X happens in the future", or "what if Y happens right now". The problem is that it's almost impossible to have a single solid definition, since almost any piece of fiction could be viewed as science fiction, depending on how you define it.
That said, most science fiction as viewed by the general public will consist of aliens, time travel, the future (at least 10 years into the future), parallel universes, travel between planets (other than the moon, unless there's a space station and moon base), or robots. Any of the above, or combination of the above is enough to label something science fiction in most people's minds.
It gets harder when science fiction starts to blur with contemporary fiction, or horror or spy fiction. Often, supernatural elements (ghosts, werewolves, vampires) aren't scifi, but horror, or fantasy, mostly because there's no science behind them. At some point, it becomes a question of what is the main focus? Often, the exploration of "what if" is the best possible answer to "what is scifi".
Time travel yes, until such time as technology can produce it.
Extra-planetary space travel? No. Apollo 13 is not a science fiction movie. I wouldn't consider Deep Impact or Armageddon to be scifi. They use advanced space ships, but not outside the realm of engineering possibility.
Something that steps just on the edge of today's accomplishments shouldn't be considered scifi (or fantasy), it has to go a little beyond that. I.e. Limitless wouldn't be a scifi, but Jurassic Park is.