Unique - 1. existing as the only one or as the sole example; single; solitary in type or characteristics: a unique copy of an ancient manuscript. 2. having no like or equal; unparalleled; incomparable: Bach was unique in his handling of counterpoint. 3. limited in occurrence to a given class, situation, or area: a species unique to Australia. 4. limited to a single outcome or result; without alternative possibilities: Certain types of problems have unique solutions. 5. not typical; unusual: She has a very unique smile.
By those definitions, their planets are not unique. If your definition of unique differs from those established by the language we are using, then you have to specify this.
I wonder how many arguments ultimately boil down to this kind of misunderstandings over words. And it doesn't help that marketers will happily use loaded words like "unique" to create hype.
I think it could be done online since there is no strict text limit and it helps with understanding.
Will try it next time.