Five small cosmic bodies, discovered in 2002 and 2003,

Answer: A

The discovery of five cosmic bodies has already been made. the total, however, has been added to 13.

Bringing fits the flow better than any other option.

Discovery caused ---> bringing to 13 the total of ...

Official explanation:
Read the Original Sentence Carefully, Looking for Errors:

To introduce action that occurs at the same time as the main action, the present participle -ing form is proper. Verbs in the gerund form (-ing form) should be treated with skepticism on the GMAT. Here, however, the "bringing to 13" happens at the same time as the designating; therefore, the -ing form "bringing" is appropriate. Suspect (A) is correct, but check all the answer choices to make sure.

Scan and Group the Answer Choices:

It's interesting to note that four answers add "and" at the beginning. Also note the split among "bringing," "brings," and "brought."

Eliminate Wrong Answer Choices:

Eliminating the remaining answer choices requires understanding what subject goes with the verb "brings" or "brought." What brought the number of moons up to 13? The designation of the cosmic bodies as moons caused the count to increase. However, the sentence uses the verb "designated" but never presents "the designation" as a noun (and hence, never as a subject). Thus, (B) and (E) cannot be correct, as the verbs "brings" and "brought" do not have a corresponding subject.

(C) and (D) use the pronoun "it," which would create a subject. However, pronouns on the GMAT must have a specific antecedent (the noun replaced by the pronoun) stated elsewhere in the sentence. "The designation" (which "it" probably refers to) was never stated. Thus, (C) and (D) cannot be correct.

With no clear error and concise, proper grammar, (A) is the correct answer.

TAKEAWAY: The -ing verb form is often questionable on the GMAT, but is acceptable for describing a secondary action that occurred alongside the main action (for example, Brady took the train home after work, reading his favorite magazine the whole time)