Van Hoolst, T., Dehant, V., & Defraigne, P. (2000). Sensitivity of the Free Core Nutation and the Chandler Wobble to changes in the interior structure of Mars. Physics of the Earth and Planetary Interiors, 117(1-4), 397-405. https://doi.org/10.1016/S0031-9201(99)00109-0 (Original work published 2000)