Marty, J. C., Balmino, G., Duron, J., Rosenblatt, P., Le Maistre, S., Rivoldini, A., Dehant, V., & Van Hoolst, T. (2009). Martian gravity field model and its time variations from MGS and Odyssey data. Planetary and Space Science, 57(3), 350-363. https://doi.org/10.1016/j.pss.2009.01.004 (Original work published 2009)