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We investigated the possible seismic signatures of dust devils on Mars, both at long and short period, based on the analysis of Earth data and on forward modeling for Mars. Seismic and meteorological data collected in the Mojave Desert, California, recorded the signals generated by dust devils. In the 10-100 s band, the quasi-static surface deformation triggered by pressure fluctuations resulted in detectable ground-tilt effects: these are in good agreement with our modeling based on Sorrells' theory. In addition, high-frequency records also exhibit a significant excitation in correspondence to dust devil episodes. Besides wind noise, this signal includes shallow surface waves due to the atmosphere-surface coupling and is used for a preliminary inversion of the near-surface S-wave profile down to 50 m depth. In the case of Mars, we modeled the long-period signals generated by the pressure field resulting from turbulence-resolving Large-Eddy Simulations. For typical dust-devil-like vortices with pressure drops of a couple Pascals, the corresponding horizontal acceleration is of a few nm/s for rocky subsurface models and reaches 10-20 nm/s for weak regolith models. In both cases, this signal can be detected by the Very-Broad Band seismometers of the InSight/SEIS experiment up to a distance of a few hundred meters from the vortex, the amplitude of the signal decreasing as the inverse of the distance. Atmospheric vortices are thus expected to be detected at the InSight landing site; the analysis of their seismic and atmospheric signals could lead to additional constraints on the near-surface structure, more precisely on the ground compliance and possibly on the seismic velocities. [ABSTRACT FROM AUTHOR]

The atmospheric pressure fluctuations on Mars induce an elastic response in the ground that creates a ground tilt, detectable as a seismic signal on the InSight seismometer SEIS. The seismic pressure noise is modeled using Large Eddy Simulations (LES) of the wind and surface pressure at the InSight landing site and a Green's function ground deformation approach that is subsequently validated via a detailed comparison with two other methods: a spectral approach, and an approach based on Sorrells' theory (Sorrells, Geophys. J. Int. 26:71-82, 1971; Sorrells et al., Nat. Phys. Sci. 229:14-16, 1971). The horizontal accelerations as a result of the ground tilt due to the LES turbulence-induced pressure fluctuations are found to be typically $\sim 2 \mbox{--} 40~\mbox{nm}/\mbox{s}^{2}$ in amplitude, whereas the direct horizontal acceleration is two orders of magnitude smaller and is thus negligible in comparison. The vertical accelerations are found to be $\sim 0.1\mbox{--}6~\mbox{nm}/\mbox{s}^{2}$ in amplitude. These are expected to be worst-case estimates for the seismic noise as we use a half-space approximation; the presence at some (shallow) depth of a harder layer would significantly reduce quasi-static displacement and tilt effects. We show that under calm conditions, a single-pressure measurement is representative of the large-scale pressure field (to a distance of several kilometers), particularly in the prevailing wind direction. However, during windy conditions, small-scale turbulence results in a reduced correlation between the pressure signals, and the single-pressure measurement becomes less representative of the pressure field. The correlation between the seismic signal and the pressure signal is found to be higher for the windiest period because the seismic pressure noise reflects the atmospheric structure close to the seismometer. In the same way that we reduce the atmospheric seismic signal by making use of a pressure sensor that is part of the InSight Auxiliary Payload Sensor Suite, we also the use the synthetic noise data obtained from the LES pressure field to demonstrate a decorrelation strategy. We show that our decorrelation approach is efficient, resulting in a reduction by a factor of $\sim 5$ in the observed horizontal tilt noise (in the wind direction) and the vertical noise. This technique can, therefore, be used to remove the pressure signal from the seismic data obtained on Mars during the InSight mission. [ABSTRACT FROM AUTHOR]

Mars atmospheric pressure variations induce ground deformations that are the main source of environmental noise on the InSight SEIS instrument. Phenomena generating pressure variations, such as meteorological wavefronts, gravity waves, convective vortices and small-scale turbulence are covering the whole frequency range of SEIS broadband seismometers. These signals impact the capability of SEIS sensors to detect seismic waves propagating in Mars interior. However, the relation between pressure variations measured by the InSight pressure sensor and ground movements measured by SEIS being essentially linear, it is possible to invert both signals to find the transfer function between pressure and ground motion. Then, pressure generated ground movements can be substracted from SEIS records in order to improve their sensitivity to seismic waves. The transfer function, usually called compliance, depends on the ground properties. Thus, the decorrelation of SEIS records from pressure effects will also allow us to constrain the subsurface properties at the InSight landing site.Our study compares two different pressure decorrelation methods applied to Mars synthetic data, and records by both short period and very broadband SEIS sensors. The pressure-decorrelation methods are presented and their differences in terms of underlying assumptions and implementations are explained. Their performances and drawbacks, analyzed on realistic synthetic datasets, are discussed. We plan to apply these methods to real Mars data and use them to retrieve the ground compliance at the InSight landing site over a broad frequency range. Accordingly, we expect to extract elastic properties of the subsurface through the compliance measurements. Wind measurements by the TWINS wind sensor will be integrated in order to separate the effects of various atmospheric phenomena. This sensor is almost identical to the Rover Environmental Monitoring Station sent to Mars as part of the Mars Science Laboratory (MSL), which operated even after the damage suffered during the MSL landing for more than two Martian years. Thus, wind measured by TWINS will provide valuable inputs to the decorrelation on the InSight SEIS instrument. Finally, the variations of decorrelation performances and compliance measurements with the diurnal Mars cycle will be analyzed. [ABSTRACT FROM AUTHOR]

• Hf/W ages of magmatic iron meteorites define a common thermal evolution. • We propose a convective model based on lab-scale experiments with internal sources. • Inversion of the Hf/W record defines a universal accretion scenario. • Accretion starts by the ≈ instantaneous formation of 60 ±30 km nuclei. • Accretion continues by ≈3 Myr of continuous pebbles accretion. The timing of formation of 100-300 km size planetesimals in the protoplanetary disk remains largely unconstrained. Recent models show that gravitational collapse of boulders in overdense regions of a dusty accretion disk can overcome the meter-sized barrier and lead to rapid formation of planetesimals with size of several km that further grow by pebble accretion. Hf/W ages indicate that the first large planetesimals to form could be the parent bodies of magmatic iron meteorites. These ages have been so far used to constrain timing of accretion considering (i) instantaneous accretion, and (ii) purely conductive heat transfer in the planetesimal. To relax these hypotheses we model the thermal evolution of a planetesimal in course of accretion and we take into account the possibility of convection onset. Our model is further based on considering the possibility of a common thermal evolution for all the parent bodies of iron meteorites. Within that framework we show that the planetesimals could have grown following a universal accretion law starting at the very beginning of the history of the disk by a nearly instantaneous formation of 60 ± 30 km size nuclei, followed by a growth via pebble accretion at a much slower pace to reach final sizes of 150–300 km in about 3 Myr. In this universal scenario, complete melting and total differentiation are not bound to happen in the parent body due to the continuous accretion of cold pebbles. The model, though calibrated here on iron meteorites, is general and can in principle be applied to other types of planetesimals such as for instance the parent bodies of CV chondrites. [ABSTRACT FROM AUTHOR]

Based on an updated model of the regolith’s elastic properties, we simulate the ambient vibrations background wavefield recorded by InSight’s Seismic Experiment for Interior Structure (SEIS) on Mars to characterise the influence of the regolith and invert SEIS data for shallow subsurface structure. By approximately scaling the synthetics based on seismic signals of a terrestrial dust devil, we find that the high-frequency atmospheric background wavefield should be above the self-noise of SEIS’s SP sensors, even if the signals are not produced within 100-200 m of the station. We compare horizontal-to-vertical spectral ratios and Rayleigh wave ellipticity curves for a surface-wave based simulation on the one hand with synthetics explicitly considering body waves on the other hand and do not find any striking differences. Inverting the data, we find that the results are insensitive to assumptions on density. By contrast, assumptions on the velocity range in the upper-most layer have a strong influence on the results also at larger depth. Wrong assumptions can lead to results far from the true model in this case. Additional information on the general shape of the curve, i.e. single or dual peak, could help to mitigate this effect, even if it cannot directly be included into the inversion. We find that the ellipticity curves can provide stronger constraints on the minimum thickness and velocity of the second layer of the model than on the maximum values. We also consider the effect of instrumentation resonances caused by the lander flexible modes, solar panels, and the SEIS levelling system. Both the levelling system resonances and the lander flexible modes occur at significantly higher frequencies than the expected structural response, i.e. above 35 Hz and 20 Hz, respectively. While the lander and solar panel resonances might be too weak in amplitude to be recorded by SEIS, the levelling system resonances will show up clearly in horizontal spectra, the H/V and ellipticity curves. They are not removed by trying to extract only Rayleigh-wave dominated parts of the data. However, they can be distinguished from any subsurface response by their exceptionally low damping ratios of 1% or less as determined by random decrement analysis. The same applies to lander-generated signals observed in actual data from a Moon analogue experiment, so we expect this analysis will be useful in identifying instrumentation resonances in SEIS data. [ABSTRACT FROM AUTHOR]

Despite its ground installation at about 1.5 meter from the lander, SEIS (Seismic Experiment for Interior Structure) will be sensitive to the ground displacement generated by the lander, in addition to direct forces from the lander propagating along the tether. This lander noise is also expected in the VBB (Very Broad Band seismometers) bandwidth, including below the gravest resonance mode of the lander, expected close or below 10 Hz. In the VBB bandwidth, the lander deck acceleration has been monitored by the SPs (Short Period seismometers) when the latter were operating on it. These measurements provide key constrains on the level of deck acceleration and possibly deck rotation and can therefore be used to predict the forces generated by the lander on the ground and to compare them with the observations made by the SEIS VBBs on the ground. We use formalism developed by Fayon et al. (2017) to model the lander and its 3 feet and complete the approach of Murdoch et al (2017) by adding the torques generated on each foot by the lander rotations, which might likely be important in the bandwidth of the VBB sensors, e.g. [0-10 Hz]. We then identify on the ground VBB signals the largest resonances in the 0-10 Hz bandwidth, including in term of polarized signals on the 3 axes components and analyze their amplitude as a function of wind level and pressure fluctuation. For all the identified VBB resonances, we repeat the analysis using the SP data on the deck. We present preliminary results and tests on a noise rejection algorithm, in order to improve the capability of the VBBs to detect non-lander atmospheric signals and seismic signals in the DC-10 Hz bandwidth. We finally conclude by discussing the opportunity offered by this lander signal to better characterize the wind flow on the lander. [ABSTRACT FROM AUTHOR]

The InSight spacecraft landed in the flat regions of Elysium Planitia on November 26th 2018. The instruments on board InSight make it capable of acting as a meteorological station at the surface of Mars. A pressure sensor (PS), two temperature and wind sensor booms (TWINS), along with the InSight FluxGate (IFG) magnetometer, form the Auxiliary Sensor Payload Suite (APSS). This is complemented by capabilities to measure surface brightness temperature by the radiometer in the Heat-Flow and Physical Properties Package (HP3) suite, to explore the impact of atmospheric processes on seismic measurements by SEIS, and to use InSight cameras to estimate atmospheric opacity (notably caused by suspended dust particles) and other atmospheric phenomena such as clouds and dust devils. We will discuss results drawn from atmospheric measurements on board InSight over the first two months of operation, highlighting new perspectives permitted by the high-frequency, continuous nature of the InSight acquisitions. Surface pressure measurements record global-to-local atmospheric phenomena: CO2 condensation (annual), dust cycle and storms (seasonal), baroclinic waves (weekly), thermal tides (daily), gravity waves (thousands of seconds), convective cells (hundreds of seconds), convective vortices (tens of seconds, leading to dust devils if dust particles are transported in the vortex). Two main large-scale wind regimes were expected from Global Climate Modeling at the InSight landing site during a typical year: towards the northwest in northern spring and summer, then in the opposite direction in southern summer. Existing in-situ measurements on Mars and Large-Eddy Simulations indicate that daytime convective vortices and cells not only impact pressure, but also temperature and winds; the nighttime atmosphere on Mars is comparatively much less turbulent and dominated by shear-driven turbulence, in contrast to the buoyancy-driven turbulence active in daytime. All such existing measurements and model predictions will be compared and challenged with InSight measurements. Seismic signatures associated with atmospheric phenomena will also be discussed, with a particular emphasis on the knowledge gained by the unprecedented measurements performed by InSight's seismometers. [ABSTRACT FROM AUTHOR]

InSight landed on Mars on November 26th, 2018 with several geophysical instruments including a short-period seismometer and a broadband seismometer (SEIS, Seismic Experiment for Interior Structure). Both seismometers are now installed directly on the Mars surface and enable to analyze the continuous seismic signal. The purpose of this study is to analyze autocorrelations of Mars continuous seismic signal. Seismic interferometry by ambient noise autocorrelations is a special case of Green's function retrieval for single-station analysis. High-frequency noise autocorrelations can be used to extract the zero-offset reflectivity and basin resonances beneath of the landing site while low-frequency noise autocorrelations contain mainly orbiting surface waves and are useful to extract normal modes. We analyze the signal by using both the classical and phase autocorrelations. Correlograms are stacked using the phase weighted stack method in order to enhance the signal to noise ratio.The method was tested also on the two blindtest datasets provided by the Marsquake Service (MQS) and by the Mars Structure Service (MSS). It is further applied to analyze the first data recorded on Mars by the co-located broadband and short period seismometers. [ABSTRACT FROM AUTHOR]

The NASA InSight mission to Mars successfully landed on November 26th, 2018 in Elysium Planitia. One of its goal is to characterize the seismic activity of Mars, which can be triggered by three main types of sources: tectonic, meteoritic, and atmospheric (e.g. turbulence). Reiss and Lorenz (2016) reported numerous tracks in the close vicinity of the InSight landing site, denoting surface changes caused by the passage of dust devils in Elysium Planitia. Large-Eddy Simulations also indicated that large pressure drops caused by dust-devil-like convective vortices are expected to be ubiquitous at the InSight landing site (Spiga et al. 2018). In this study we validate our methodology on high resolution satellite images (HiRISE) that have been acquired before the landing of InSight (May and July 2014) and analyze a preliminary set of images acquired after the landing (e.g., December 6th and 11th, 2018). We will explore how the formation of new dust devil tracks can be evidenced in sets of successive HiRISE images acquired a couple of sols apart. Tracks are characterized by dark linear traces ranging from a few meters to more than ten meters wide and oriented in the ambient wind direction, that can be directly compared to wind direction recorded by the InSight lander's meteorological package. Detailed analyses are performed in order to determine the distribution of azimuths, sizes, and distances from the lander, of each dust devil passage identified on the HiRISE images. All the information will be useful to better link dust devils with their signatures recorded by the pressure and seismic measurements carried out by the APSS and SEIS instruments on board InSight. Moreover, forthcoming HiRISE observations will be used to further characterize ongoing dust devil activity and improve the statistics of those events. The set of HiRISE images collected during the InSight mission can also be employed to detect potential new meteoritic impact that could act as seismic sources. [ABSTRACT FROM AUTHOR]

The upper part of the Mars’ interior (comprising crust and upper mantle) can be described byclassical well-known elastic isotropic parameters (V P, V S, and ρ) and further byinferring additional anisotropic parameters carried by seismic waveforms. In theview of providing a mean 1D reference model for at least the first 300 km of theMars’ interior, surface waves are well-suited since they are travelling guided bythe planet’s surface. At first order, the dispersive property of these waves reflectsradial heterogeneities of the sampled medium, integrated along the travel path.In the event of a marsquake, the surface waves are propagating along minor- andmajor arcs then providing informations on different media. Although Rayleighwaves are widely used to infer the isotropic seismic structure, Love waves can beused to constrain anisotropy. Since azimuthal dependence of seismic waves cannotbe resolved with a single station as InSight, only the polarization anisotropy canbe retrieve. In the framework of the Mars Structure Service blind test, providinga single event dataset, we present results and show that vertical polarization ofS-waves significantly differs from horizontal only within the first 20 km depth. Thetransverse anisotropy measured by η seems to be inexistent in the input model. [ABSTRACT FROM AUTHOR]

The InSight lander successfully delivered geophysical instrument package on the Martian surface on November 26th, 2018, including a broadband and a short-period seismometer (Seismic Experiment for Interior Structure, SEIS). The seismic instrument package is specifically designed to record marsquakes and meteoritic impacts in Martian conditions. Routine operations are split into two services: the Mars Structure Service (MSS) and the Marsquake Service (MQS), which are responsible for defining structure models and seismicity catalogs, respectively. The first "deliverable" of the MSS will be a model based on the events detected during the first 3 months of seismic monitoring of the mission, for which only a few quakes might be expected based on current estimates of Mars seismic activity. To test our approach of determining the interior model of Mars and to prepare the InSight science team for data return, we made use of a "blind test" time series for which the Marsquake parameters (location, depth, origin time, and moment tensor) and interior model were unknown to the group at large.In preparation for the mission, the goal was to develop mature algorithms to handle the data as efficiency as possible. Synthetic seismic waveforms were computed in a 1D mantle model with a 3D crust on top using AxiSEM and Salvus. The time series were created by adding seismic noise that relies on pre-landing estimates of noise generated by the sensors, electronic system, environment, and nearby lander. To characterize what we could learn about Mars interior structure with only one station and with the first seismic event, we performed inversions of a synthetic data following a blind test process, where the interior model was unknown to all team members carrying out data analysis and inversion. We detail and compare the results of this "blind test" using different methods including inversion of surface wave dispersion data, body waves travel times, and the waveforms themselves. We have used mainly Bayesian techniques to obtain robust probability density functions of interior structure parameters. The effects on the retrieved model distributions of fixing mars quake location and origin time are investigated, as is the effect of using fixed Vs flexible parameterizations. To allow for tighter constraints, we also test the use of priors based on thermodynamically-constrained models together with seismic observations, as well as seismic confirmation/rejection of models purely based on thermodynamical modelling. These techniques considered here form a large part of the planned modeling of the MSS that will be ultimately employed with the first recording of a seismic event by InSight. [ABSTRACT FROM AUTHOR]

In November 2018, for the first time a dedicated geophysical station, the InSight lander, will be deployed on the surface of Mars. Along with the two main geophysical packages, the Seismic Experiment for Interior Structure (SEIS) and the Heat-Flow and Physical Properties Package (HP3), the InSight lander holds a highly sensitive pressure sensor (PS) and the Temperature and Winds for InSight (TWINS) instrument, both of which (along with the InSight FluxGate (IFG) Magnetometer) form the Auxiliary Sensor Payload Suite (APSS). Associated with the RADiometer (RAD) instrument which will measure the surface brightness temperature, and the Instrument Deployment Camera (IDC) which will be used to quantify atmospheric opacity, this will make InSight capable to act as a meteorological station at the surface of Mars. While probing the internal structure of Mars is the primary scientific goal of the mission, atmospheric science remains a key science objective for InSight. InSight has the potential to provide a more continuous and higher-frequency record of pressure, air temperature and winds at the surface of Mars than previous in situ missions. In the paper, key results from multiscale meteorological modeling, from Global Climate Models to Large-Eddy Simulations, are described as a reference for future studies based on the InSight measurements during operations. We summarize the capabilities of InSight for atmospheric observations, from profiling during Entry, Descent and Landing to surface measurements (pressure, temperature, winds, angular momentum), and the plans for how InSight’s sensors will be used during operations, as well as possible synergies with orbital observations. In a dedicated section, we describe the seismic impact of atmospheric phenomena (from the point of view of both “noise” to be decorrelated from the seismic signal and “signal” to provide information on atmospheric processes). We discuss in this framework Planetary Boundary Layer turbulence, with a focus on convective vortices and dust devils, gravity waves (with idealized modeling), and large-scale circulations. Our paper also presents possible new, exploratory, studies with the InSight instrumentation: surface layer scaling and exploration of the Monin-Obukhov model, aeolian surface changes and saltation / lifing studies, and monitoring of secular pressure changes. The InSight mission will be instrumental in broadening the knowledge of the Martian atmosphere, with a unique set of measurements from the surface of Mars. [ABSTRACT FROM AUTHOR]