SC Pronoun Question

[rjcesaro]

I have a question from the sentence correction bin of questions on the MGMAT website. The sentence is:

Though viewed from a distance, Saturn's main rings may appear to be smooth and continuous, they are in fact composed of thousands of separate icy ringlets when viewed up close.

All of the answer choices include "they" or "them" in order to refer back to Saturn's main rings. In the pronoun chapter, however, it says that according to the Possessive Poison rule, possessive nouns can only serve as antecedents to possessive pronouns, not to subject or object pronouns. The correct answer uses "them", which is an object pronoun. It seems to me that "Saturn's main rings" is possessive but perhaps I am missing something.......Could someone please provide me with an explanation? Thanks for your help and time. Here is the correct answer:

When viewed from a distance, Saturn's main rings may appear smooth and continuous, but closer viewing reveals them to be composed of thousands of separate icy ringlets.

[StaceyKoprince]

This rule is very confusing and people almost always apply it incorrectly. In addition, it is almost never tested on the test. Honestly? I'd forget about this rule entirely.

In the phrase "Saturn's main rings," the word "Saturn's" is a possessive noun - ONLY the word "Saturn's." The word "rings" is a regular noun. The pronoun is referring to the regular noun.