Detection of the Chandler Wobble of Mars from Orbiting Spacecraft

AbstractFor the first time for any planetary body other than the Earth, the free wobble of the pole called the or Chandler wobble of the pole has been detected for Mars with a period of 206.9 ± 0.5 days and amplitude of 10-cm from the tracking observations of the Mars Odyssey spacecraft, Mars Reconnaissance Orbiter (MRO), and Mars Global Surveyor (MGS), in order of decreasing sensitivity. The motion of the rotation pole location on the surface of Mars or polar motion, is observed using two different approaches: (1) global estimates of the Mars’ orientation together with the gravity field of Mars, and (2) as observed through the time-varying solutions of the C21 and S21 gravity coefficients. For Mars interior models, the Chandler wobble period is combined with other Mars measurements of the interior including the moments of inertia from an updated precession rate ψ ̇=-7603.9±1.3 "mas/yr" and the tidal Love number k2 = 0.169 ± 0.006 from Konopliv et al. (2016). The Chandler wobble period allows to better constrain the rheology of the Martian mantle and in particular its long term frequency dependence.