I'm aware that the English translation of this expression is simply including. However, I came across this article in which they explained that although in English it is correct to use including to make an enumeration, in French, y compris doesn't quite work like that.
This year my students are studying several planets, including Mars, Venus and Earth.
Cette année, mes élèves étudient plusieurs planètes, *y compris Mars, Vénus et la Terre.
Nonetheless, I'm not entirely sure if I understand why? There is this example that shows the correct use of the expression:
Il a servi à boire à tout le monde, y compris à ses ennemis.
If I rephrase the original sentence about planets & make it similar to the one above so it looks like this, would it be okay?
This year my students are studying several planets, including the planets of the solar system.
Cette année, mes élèves étudient plusieurs planètes, y compris aux planetes du systeme solaire.
But, if that is correct, how come it turns out to be incorrect when I replace "planets of the solar system" for the actual planets?