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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
Geophysical and cosmochemical evidence for a volatile-rich Mars
Constraints on the composition of Mars principally derive from chemical analyses of a set of Martian meteorites that rely either on determinations of their refractory element abundances or isotopic compositions. Both approaches, however, lead to models of Mars that are unable to self-consistently explain major element chemistry and match its observed geophysical properties, unless ad hoc adjustments to key parameters, namely, bulk Fe/Si ratio, core composition, and/or core size are made. Here, we combine geophysical observations, including high-quality seismic data acquired with the InSight mission, with a cosmochemical model to constrain the composition of Mars. We find that the FeO content of Mars' mantle is 13.7±0.4 wt%, corresponding to a Mg# of 0.81±0.01. Because of the lower FeO content of the mantle, compared with previous estimates, we obtain a higher mean core density of 6150±46 kg/m3 than predicted by recent seismic observations, yet our estimate for the core radius remains consistent around 1840±10 km, corresponding to a core mass fraction of 0.250±0.005. Relying on cosmochemical constraints, volatile element behaviour, and planetary building blocks that match geophysical and isotopic signatures of Martian meteorites, we find that the liquid core is made up of 88.4±3.9 wt% Fe-Ni-Co with light elements making up the rest. To match the mean core density constraint, we predict, based on experimentally-determined thermodynamic solution models, a light element abundance in the range of ≈9 wt% S, ⩾3 wt% C, ⩽2.5 wt% O, and ⩽0.5 wt% H, supporting the notion of a volatile-rich Mars. To accumulate sufficient amounts of these volatile elements, Mars must have formed before the nebular gas dispersed and/or, relative to Earth, accreted a higher proportion of planetesimals from the outer protoplanetary disk where volatiles condensed more readily.ISSN:0012-821XISSN:1385-013