TTVs measured for Kepler-139d (red), Kepler-139b (blue), and Kepler-139c (green). In the top row, the black curves are based on a model fitted to the TTVs and RVs that includes only the four previously known planets. The four-planet model fails to reproduce the 30 minute TTVs of planet c. In the bottom row, the black curves are based on a five-planet model, including a 45 M_⊕ nontransiting planet with a period of 354 days, placing it wide of the 2:1 MMR with planet c. The five-planet model provides a far superior fit (﹩{\rm{\Delta }}{\chi }_{{\rm{TTV}}}^{2}\,=\,60﹩).