Complex sentence: Prior to the rendevouz with Earth, the asteroid had a poorly constrained orbit, but often will make close approaches to our planet, and the predictions was calculated to occur sometime between March 6--10,2016.
Split into simpler sentences: Prior to the rendevouz with Earth, the asteroid had a poorly constrained orbit, but often will make close approaches to our planet. One such approach was calculated to occur sometime between March 6--10,2016.