Abstract
AbstractThe tidal response of Mars, due to the Sun and the Martian moons, Phobos and Deimos, provides information about the interior structure of Mars. By using the Very Broad Band (VBB) seismometer of Seismic Experiment for Interior Structure (SEIS) as a gravimeter on the surface of Mars, the InSight mission will provide the long‐period data suited to tidal analysis: most notably, the proximity of Phobos implies that degree 2, 3, 4, and further tides will be detectable by the VBB and are expected to provide information about the rheology at different depths within Mars. In order to expedite the recovery of these tidal signals in the SEIS measurements, we model the tides raised by Phobos using a tidal potential deduced from JPL Horizons ephemerides. From this potential, we calculate the expected tidal acceleration at InSight's location and gravimetric factors using a set of plausible interior models of Mars. To simulate the expected long period signal on the VBB seismometer, we use the InSight Auxiliary Payload Sensor Suite data to model the noise seen at low frequency by SEIS mainly due to temperature and pressure variations. Based on this synthetic signal, by applying filtering methods such as stacking and matched filtering to these synthetic data, we show that by recovering the gravimetric factors, it should be possible to constrain the state of the core and its size with an accuracy of 125 km after two Earth years.
Highlights
The tides of Phobos raised on Mars can help constraining the internal structure of Mars (Bills et al, 2005; Lognonné & Mosser, 1993)
By using the Very Broad Band (VBB) seismometer of Seismic Experiment for Interior Structure (SEIS) as a gravimeter on the surface of Mars, the InSight mission will provide the long-period data suited to tidal analysis: most notably, the proximity of Phobos implies that degree 2, 3, 4, and further tides will be detectable by the VBB and are expected to provide information about the rheology at different depths within Mars
We construct a forward model of the Phobos tides up to a degree l = 4, and update the noise model experienced by SEIS at low frequencies with the new environmental data measured with InSight's Auxiliary Payload Sensor Suite (APSS) at the surface of Mars (Banerdt et al, 2020; Banfield et al, 2020)
Summary
The tides of Phobos raised on Mars can help constraining the internal structure of Mars (Bills et al, 2005; Lognonné & Mosser, 1993). The Seismic Experiment for Interior Structure instrument (SEIS) of the InSight mission, when being used as a gravimeter on the surface of Mars, has a resolution that is good enough to be able to detect the gravitational signature induced by Phobos tides of degree 2, 3, and 4 (Lognonné et al, 2019). We construct a forward model of the Phobos tides up to a degree l = 4, and update the noise model experienced by SEIS (based on previous works from Mimoun et al, 2017 and Pou et al, 2018) at low frequencies with the new environmental data measured with InSight's Auxiliary Payload Sensor Suite (APSS) at the surface of Mars (Banerdt et al, 2020; Banfield et al, 2020). While the decorrelation process is currently less effective due to nonlinear effects, the current trend indicates that the real Phobos tides should be detectable enough to constrain the core radius with two Earth years’ worth of the data
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