The issue with that translation is that you are breaking up what is predicated of the planetary societies.

(Every planetary society) (will be endangered by impacts from space.)

The word "by" is a modifier that explains the type of endangerment. If you split it up as you have, you then lose this modification and your predicate becomes "will be endangered" which is losing the specificity of the claim. Those specifics are very important on the LSAT and ignoring the "by" is a misinterpretation of the claim that will lead to wrong answers.

your username gave me a chuckle. the struggle is real.

Cogent is a term used to describe inductive arguments. An inductive argument is "strong" if the conclusion is very likely to follow from the premises. A "Cogent" argument is a strong inductive argument, with all of its premises actually being true.

Think of it this way: when you first read the stimulus, it's pretty clear that there are two conclusions: 1- The proposal to allow phone use on planes is ill-advised. 2- Cell phone use on planes would be far more annoying than on trains and buses. Ask yourself, does the proposal being ill-advised somehow lend support to the idea that using phones on planes would be far more annoying? or the other way around? I think once you ask yourself that, it becomes clear that extreme annoyance would more lend itself to something being ill-advised, rather than the other way around. Whichever conclusion lends support to another is your sub-conclusion, whichever is supported by another conclusion is your main conclusion.