Signatures of the Martian rotation parameters in the Doppler and range observables

The position of a Martian lander is affected by different aspects of Mars' rotational motions: the nutations, the precession, the length-of-day variations and the polar motion. These various motions have a different signature in a Doppler observable between the Earth and a lander on Mars' surface. Knowing the correlations between these signatures and the moments when these signatures are not null during one day or on a longer timescale is important to identify strategies that maximize the geophysical return of observations with a geodesy experiment, in particular for the ones on-board the future NASA InSight or ESA-Roscosmos ExoMars2020 missions. We provide first-order formulations of the signature of the rotation parameters in the Doppler and range observables. These expressions are functions of the diurnal rotation of Mars, the lander position, the planet radius and the rotation parameter. Additionally, the nutation signature in the Doppler observable is proportional to the Earth declination with respect to Mars. For a lander on Mars close to the equator, the motions with the largest signature in the Doppler observable are due to the length-of-day variations, the precession rate and the rigid nutations. The polar motion and the liquid core signatures have a much smaller amplitude. For a lander closer to the pole, the polar motion signature is enhanced while the other signatures decrease. We also numerically evaluate the amplitudes of the rotation parameters signature in the Doppler observable for landers on other planets or moons.Comment: 30 pages 7 figures, In press PS

The coupling between inertial and rotational eigenmodes in planets with liquid cores

The Earth is a rapidly rotating body. The centrifugal pull makes its shape resemble a flattened ellipsoid and Coriolis forces support waves in its fluid core, known as inertial waves. These waves can lead to global oscillations, or modes, of the fluid. Periodic variations of the Earth's rotation axis (nutations) can lead to an exchange of angular momentum between the mantle and the fluid core and excite these inertial modes. In addition to viscous torques that exist regardless of the shape of the boundaries, the small flattening of the core-mantle boundary (CMB) allows inertial modes to exert pressure torques on the mantle. These torques effectively couple the rigid-body dynamics of the Earth with the fluid dynamics of the fluid core. Here we present the first high resolution numerical model that solves simultaneously the rigid body dynamics of the mantle and the Navier-Stokes equation for the liquid core. This method takes naturally into account dissipative processes in the fluid that are ignored in current nutation models. We find that the Free Core Nutation (FCN) mode, mostly a toroidal fluid flow if the mantle has a large moment of inertia, enters into resonance with nearby modes if the mantle's moment of inertia is reduced. These mode interactions seem to be completely analogous to the ones discovered by Schmitt (2006) in a uniformly rotating ellipsoid with varying flattening.Comment: 30 pages, 19 figures. Published in the Geophysical Journal Internationa

Inertial modes of a freely rotating ellipsoidal planet and their relation to nutations

We compute the inertial modes of a freely rotating two-layer planetary model with an ellipsoidal inviscid fluid core and a perfectly rigid mantle. We present a method to derive analytical formulae for the frequencies of the Free Core Nutation (FCN) and Chandler Wobble (CW) which are valid to all orders of the dynamical flattening of the core and mantle, and we show how the FCN and CW are the direct generalisation of the purely fluid Spin-Over mode (SO) and of the Eulerian Wobble (EW) to the case where the mantle can oscillate freely around a state of steady rotation. Through a numerical computation for an axisymmetric (oblate spheroidal) planet, we demonstrate that all other inertial modes of the steadily rotating fluid core are also free modes of the freely rotating two-layer planet.Comment: 19 pages, 4 figures, accepted for publication in Planetary Science Journal (AAS

Short Report of IVS Working Group 5 (WG5) on Space Science Applications - An IVS Perspective

No abstract availabl

Exploring planets and asteroids with 6DoF sensors: Utopia and realism

A 6 degrees-of-freedom (6DoF) sensor, measuring three components of translational acceleration and three components of rotation rate, provides the full history of motion it is exposed to. In Earth sciences 6DoF sensors have shown great potential in exploring the interior of our planet and its seismic sources. In space sciences, apart from navigation, 6DoF sensors are, up to now, only rarely used to answer scientific questions. As a first step of establishing 6DoF motion sensing deeper into space sciences, this article describes novel scientific approaches based on 6DoF motion sensing with substantial potential for constraining the interior structure of planetary objects and asteroids. Therefore we estimate 6DoF-signal levels that originate from lander–surface interactions during landing and touchdown, from a body’s rotational dynamics as well as from seismic ground motions. We discuss these signals for an exemplary set of target bodies including Dimorphos, Phobos, Europa, the Earth’s Moon and Mars and compare those to self-noise levels of state-of-the-art sensors

Planned Products of the Mars Structure Service for the InSight Mission to Mars

Abstract The InSight lander will deliver geophysical instruments to Mars in 2018, including seismometers installed directly on the surface (Seismic Experiment for Interior Structure, SEIS). Routine operations will be split into two services, the Mars Structure Service(MSS) and Marsquake Service (MQS), which will be responsible, respectively, for defining the structure models and seismicity catalogs from the mission. The MSS will deliver a series of products before the landing, during the operations, and finally to the Planetary Data System (PDS) archive. Prior to the mission, we assembled a suite of a priori models of Mars, based on estimates of bulk composition and thermal profiles. Initial models during the mission will rely on modeling surface waves and impact-generated body waves independent of prior knowledge of structure. Later modeling will include simultaneous inversion of seismic observations for source and structural parameters. We use Bayesian inversion techniques to obtain robust probability distribution functions of interior structure parameters. Shallow structure will be characterized using the hammering of the heatflow probe mole, as well as measurements of surface wave ellipticity. Crustal scale structure will be constrained by measurements of receiver function and broadband Rayleigh wave ellipticity measurements. Core interacting body wave phases should be observable above modeled martian noise levels, allowing us to constrain deep structure. Normal modes of Mars should also be observable and can be used to estimate the globally averaged 1D structure, while combination with results from the InSight radio science mission and orbital observations will allow for constraint of deeper structure