InSight for seismically detectability and seismically triggered avalanches on Mars

International audienceGranular avalanches such as slope streaks, have been observed on Mars since the beginning of the high resolution era with MOC on MGS. Such mass wasting processes are active and their dynamics has a few implications in terms of climatic conditions. However, understanding the slope streaks dynamics is still undergoing. Many authors have proposed dry spreading of fine dust or wet processes (e.g., Schorghofer et al., 2002; 2007). For instance, Head et al., (2007) have proposed spring discharge involving salty ground-water. Many of those studies have been performed from interpretations of geomorphic features by comparing knowing processes occurring on Earth and/or a few comparisons with experimental works. Consequently, a key parameter is the triggering conditions, along with the dynamical behavior of these avalanches. We hence propose a combined approach involving numerical simulations, seismology and orbital imagery in order to provide new insights.</p> <p><strong>Orbital image constraints</strong></p> <p>We investigate the orbital images from CTX and HiRISE cameras, both onboard MRO spacecraft. They provide a complete coverage of the two regions of interest being the InSight landing site (135.61ºE 4.49ºN) and the vicinity of the large quake (170.85ºE, 7.05ºS, being at 37º from the SEIS instrument) named 1222 which occurred on 5 May 2020. In both areas, we identified many past avalanche events (Figure 1-A). More specifically, we investigate the complete set of orbital data (imagery, topography, and thermo-physical properties) to estimate in particular the rate of formation of these avalanches in the vicinity of the 1222 event location (Fig. 1-B,C). This has led to request new orbital observations targeted to the most favorable areas for avalanches and hence try to link the ground acceleration resulting from the 1222 event with the triggering of new avalanches by using detection techniques (Fig. 1-D). This work, essentially observational, is combined with the following part on the detectability of this type of source by the SEIS sensor.</p> <p><img src="" alt="" /></p> <p><strong>Figure 1 -</strong> (A) Location of identifiable landslides and avalanches (rockfall sign) around the InSight landing site (symbolized with the SEIS/WTS sign). The circles show epicentral distance from the receiver at 5º (red), 10º (orange), 15º (yellow) and 20º (light gray), which correspond to ∼300, ∼600, ∼900 and ∼1200 km respectively. Active avalanches (slope streaks) are detected at 150°E. (B) Location of active avalanches (rockfall sign) around the 1222 event location (green flag). (C) Examples of avalanches in the vicinity of the 1222 event location as seen by the CTX camera. This image was taken in May 2011 and reflects the high occurrence of such processes in the area. (D) Detection of slope streaks (and old craters) from neural networks (i.e., using darknet algorithm). </p> <p> </p> <p> </p> <p><strong>Dynamics and source function of avalanches from numerical simulations</strong></p> <p>In order to generate synthetic seismic sources due to gravity-driven sediment transport we based our simulations on a depth-averaged Saint-Venant equations model, named SHATLOP, which accounts for the curvature of the topography and on various frictional behavior for the source term following (Lucas & Mangeney, 2007; Lucas et al., 2011;2014). Volumes involved are around 8,000-40,000 m3 with a total drop height up to 1 km.  The typical duration of the event is of a few minutes up to 20 minutes for a +2 km runout slope streaks, depending on the frictional law considered and small fluctuation on the bottom topography, which  generates surges as shown on Fig. 2-A. ​​The source is considered as a point force applied at the surface from the spatial integration of the avalanche resultant force, where the velocity, the resistance force, the density of the flow and the acceleration due to gravity accounting for the bottom topography curvature are all taken into account (Fig. 2-B). The velocity models are obtained after geological considerations after Pan et al., (2019), where active mass wasting processes have been identified (Fig. 2-C). Examples of resulting seismograms are shown in Fig. 2-D.  The velocity model, still under investigation for Mars, is also an important open issue that has a strong impact on the resulting seismic signal. Finally, depending on source functions, velocity models, such an event may be detectable, in particular when occurring during the night at local time of the sensors, when the noise level is low and when spectral content is above SEIS sensitivity (Fig. 2-E).</p> <p> </p> <p><img src="" alt="" width="503" height="741" /></p> <p><strong>Figure 2 -</strong> (A) Example numerical simulation of a martian dust avalanche over a DTM generated from HiRISE stereo pair (Color scales with the velocity). (B) Resulting source force history. (C) Example of a velocity and attenuation model for Mars. (D) Synthetic seismograms accounting source distance for various velocity models and epicentral distances. (E) ADS example for a small event at 140 km.</p> <p> </p> <p><strong>References</strong></p> <p>Head, J., Marchant, D., Dickson, J.,Levy, J., Morgan, G. Slope streaks in the Antarctic Dry Valleys: Characteristics, candidate formation mechanisms, and implications for slope streak formation in the Martian environment. 7 th International Conf. (2007)</p> <p>Lucas A., and A. Mangeney. “Mobility and topographic effects for large Valles Marineris landslides on Mars”. In: <em>Geophys. Res. Lett., 34, L10201 </em>(2007)</p> <p>Lucas A., et al. “Influence of the scar geometry on landslide dy-namics and deposits: Application to Martian landslides”. In: <em>J. Geophys. Res. - Planets, 116, E10001 </em>(2011)</p> <p>Lucas, A., A. Mangeney, and J-P. Ampuero. “Frictional velocity-weakening in landslides on Earth and on other planetary bodies”. In: <em>Nature Comm.,5:3417 </em>(2014)</p> <p>Pan L.,  et al. “Crust stratigraphy and heterogeneities of the first kilometers at the dichotomy boundary in western Elysium Planitia and implications for InSight lander”. In: Icarus (2019)</p> <p>Schorghofer N., Aharonson O., and Khatiwala S. “Slope streaks on Mars: Correlations with surface properties and the potential role of water”. In: <em>Geophys. Res. Lett.,29(23) </em>(2002)</p> <p>Schorghofer, N., Aharonson, O.,  Gerstell, M. & Tatsumi, L. Three decades of slope streak activity on Mars. Icarus. 191. 132-140 (2007)</p> <p><br /><br /><br /></p&gt

Widespread Exposures of Extensive Clean Shallow Ice in the Mid-Latitudes of Mars

International audienceAlthough ice in the Martian midlatitudes is typically covered by a layer of dust or regolith, it is exposed in some locations by fresh impact craters or in erosional scarps. In both cases, the exposed ice is massive or excess ice with a low lithic content. We find that erosional scarps occur between 50° and 61° north and south latitude and that they are concentrated in and near Milankovič crater in the northern hemisphere and southeast of the Hellas basin in the southern hemisphere. These may represent locations of particularly thick or clean bodies of ice. Pits created by retreat of the scarps represent sublimation‐thermokarst landforms that evolve in a manner distinct from other ice‐loss landforms on Mars. New impact craters reveal that clean subsurface ice is widespread at middle‐ and high‐latitudes in both hemispheres at depths less than 1 m. Both the depth to ice and the ice content appear to exhibit significant variability over tens to hundreds of meters. The lowest‐latitude exposed ice is near 39°N and is at the edge of a region where impact exposures between 40° and 50°N are common, consistent with other indications of a high ice content. This lowest‐latitude ice may be currently unstable and subliming. Impact craters on lineated valley fill excavate ice blocks that may represent the top of debris‐covered glacial ice. Together, these landforms indicate widespread, clean subsurface ice at middle‐latitudes on Mars. The distribution and properties of this ice could provide information about past climate conditions

A Large New Crater Exposes the Limits of Water Ice on Mars

Abstract Water ice in the Martian mid‐latitudes has advanced and retreated in response to variations in the planet's orbit, obliquity, and climate. A 150 m‐diameter new impact crater near 35°N provides the lowest‐latitude impact exposure of subsurface ice on Mars. This is the largest known ice‐exposing crater and provides key constraints on Martian climate history. This crater indicates a regional, relatively pure ice deposit that is unstable and has nearly vanished. In the past, this deposit may have been tens of meters thick and extended equatorward of 35°N. We infer that it is overlain by pore ice emplaced during temporary stable intervals, due to recent climate variability. The marginal survival of ice here suggests that it is near the edge of shallow ice that regularly exchanges with the atmosphere

Two seismic events from InSight confirmed as new impacts on Mars

We report confirmed impact sources for two seismic events on Mars detected by the NASA InSight mission. These events have been positively associated with fresh impact craters identified from orbital images, which match predicted locations and sizes to within a factor of three, and have formation time constraints consistent with the seismic event dates. They are both of the Very High Frequency family of seismic events and present with chirps (dispersed infrasound/acoustic waves). This brings the total number of confirmed martian impact-related seismic events to eight thus far. All seismic events with chirp signals have now been confirmed as having been caused by impact cratering events. This includes all seismic activity within 100 km of the lander, and two out of the four events with source locations between 100-300 km distance

Two Seismic Events from InSight Confirmed as New Impacts on Mars

We report confirmed impact sources for two seismic events on Mars detected by the NASA InSight mission. These events have been positively associated with fresh impact craters identified from orbital images, which match predicted locations and sizes to within a factor of 3, and have formation time constraints consistent with the seismic event dates. They are both of the very high frequency family of seismic events and are present with chirps (dispersed infrasound/acoustic waves). This brings the total number of confirmed Martian impact-related seismic events to eight thus far. All seismic events with chirp signals have now been confirmed as having been caused by impact cratering events. This includes all seismic activity within 100 km of the lander and two out of the four events with source locations between 100 and 300 km distance.ISSN:2632-333

Newly formed craters on Mars located using seismic and acoustic wave data from InSight

International audienceMeteoroid impacts shape planetary surfaces by forming new craters and alter atmospheric composition. During atmospheric entry and impact on the ground, meteoroids excite transient acoustic and seismic waves. However, new crater formation and the associated impact-induced mechanical waves have yet to be observed jointly beyond Earth. Here we report observations of seismic and acoustic waves from the NASA InSight lander’s seismometer that we link to four meteoroid impact events on Mars observed in spacecraft imagery. We analysed arrival times and polarization of seismic and acoustic waves to estimate impact locations, which were subsequently confirmed by orbital imaging of the associated craters. Crater dimensions and estimates of meteoroid trajectories are consistent with waveform modelling of the recorded seismograms. With identified seismic sources, the seismic waves can be used to constrain the structure of the Martian interior, corroborating previous crustal structure models, and constrain scaling relationships between the distance and amplitude of impact-generated seismic waves on Mars, supporting a link between the seismic moment of impacts and the vertical impactor momentum. Our findings demonstrate the capability of planetary seismology to identify impact-generated seismic sources and constrain both impact processes and planetary interiors

Newly formed craters on Mars located using seismic and acoustic wave data from InSight

International audienc

Isotope ratios of H, C, and O in CO2 and H2O of the Martian atmosphere

Stable isotope ratios of H, C, and O are powerful indicators of a wide variety of planetary geophysical processes, and for Mars they reveal the record of loss of its atmosphere and subsequent interactions with its surface such as carbonate formation. We report in situ measurements of the isotopic ratios of D/H and O-18/O-16 in water and C-13/C-12, O-18/O-16, O-17/O-16, and (CO)-C-13-O-18/(CO)-C-12-O-16 in carbon dioxide, made in the martian atmosphere at Gale Crater from the Curiosity rover using the Sample Analysis at Mars (SAM)'s tunable laser spectrometer (TLS). Comparison between our measurements in the modern atmosphere and those of martian meteorites such as ALH 84001 implies that the martian reservoirs of CO2 and H2O were largely established similar to 4 billion years ago, but that atmospheric loss or surface interaction may be still ongoing