<p>New data show that saturn's rings probably orbiting the planet billions of years ago, overturning scientist's earlier belief that the rings are only about 100 million years old. </p>
<p>I know why my answer was wrong but I don't understand why this one is right.
Isn't it a run on sentence? </p>
<p>A run-on sentence contains multiple independent clauses separated by no punctuation. A comma splice is the same, except that the clauses are separated by a comma. Neither of those describes the sentence you have posted.</p>
<p>I’m assuming that you have typed the sentence incorrectly, and that “orbiting” should be something else. If you typed the sentence exactly as it appears in the original, then there is no independent clause. Technically, that would make it a sentence fragment, but it is more likely misprinted.</p>
<p>New data show that saturn’s rings were probably orbiting the planet billions of years ago, overturning scientist’s earlier belief that the rings are only about 100 million years old.
You’re right a forgot the were</p>
<p>There is nothing wrong with that sentence. Everything before the comma is an independent clause. Everything after is a participial phrase; you can think of that phrase as an adjective modifying “data” or as an adverb that modifies the entire clause; I’m partial to the adjectival analysis myself, but it doesn’t really matter.</p>
<p>You can recognize a participle by the “-ing” ending or the preterite form ("-ed" in the case of regular verbs); the implied subject is frequently in an adjacent clause. Participial phrases are not clauses themselves, so the rules about run-ons and comma splices do not apply.</p>
<p>Is there something in particular about this sentence that makes you think it’s incorrect? I would think you’ve seen this pattern thousands of times.</p>
<p>I thought the second part was independent but now I see why it isn’t.
Thx</p>