Which of the following would MOST LIKELY act as a transition sentence?

This is correct because it begins with the transition phrase, “on the contrary”, which signals a change in the direction of the discussion.
"Ultimately, no one is certain whether or not life exists elsewhere." This is incorrect because the use of the word “ultimately” suggests that it is a concluding sentence.
"Have you ever considered the possibility of life on other planets?". This is incorrect because a question would best serve as a thought-provoking topic or closing sentence.
"Scientists previously identified what appeared to be tracks on the moon." This is incorrect because it is a detail that supports a main idea.