Complex sentence: As of 2006 there were two theories for what could cause such a shift in shape: the orbit of Enceladus may have migrated inward, leading to an increase in Enceladus's rotation rate.
Split into simpler sentences: As of 2006 there were two theories for what could cause such a shift in shape. First, the orbit of Enceladus may have migrated inward, leading to an increase in Enceladus's rotation rate.