Scientists calculated that the asteroid, traveling at 46,000 miles an

Scientists calculated that the asteroid, traveling at 46,000 miles an hour, is on an elliptical path that orbits the Sun once a year and regularly brings it back toward Earth.

(A) hour, is on an elliptical path that orbits the Sun once a year and regularly brings it -> "it" refers back to "Sun" or "the asteroid". Pronoun error. Incorrect.

(B) hour, is orbiting the Sun once a year on an elliptical path that regularly brings it -> Now, "it" refers back to "the asteroid" which makes sense. Further, Orbiting is taking about "the asteroid". Meaning wise, progressive tense makes sense too. Let's keep it. If we get a better one, we can drop the option.

(C) hour, once a year orbits the Sun, regularly bringing it on an elliptical path -> again we have "it" refers back to "sun". Incorrect.

(D) hour and orbiting the Sun once a year on an elliptical path, regularly bringing it -> we don't have verb here. Incorrect.

(E) hour, orbits the Sun on an elliptical path once a year and that regularly brings it -> It is the closest to correct option. There is a small issue, "and" conjunction is not required. Incorrect.

So, I think B.