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We present the first observations of seismic waves propagating through the core of Mars. These observations, made using seismic data collected by the InSight geophysical mission, have allowed us to construct the first seismically constrained models for the elastic properties of Mars' core. We observe core-transiting seismic phase SKS from two farside seismic events detected on Mars and measure the travel times of SKS relative to mantle traversing body waves. SKS travels through the core as a compressional wave, providing information about bulk modulus and density. We perform probabilistic inversions using the core-sensitive relative travel times together with gross geophysical data and travel times from other, more proximal, seismic events to seek the equation of state parameters that best describe the liquid iron-alloy core. Our inversions provide constraints on the velocities in Mars' core and are used to develop the first seismically based estimates of its composition. We show that models informed by our SKS data favor a somewhat smaller (median core radius = 1,780 to 1,810 km) and denser (core density = 6.2 to 6.3 g/cm3) core compared to previous estimates, with a P-wave velocity of 4.9 to 5.0 km/s at the core-mantle boundary, with the composition and structure of the mantle as a dominant source of uncertainty. We infer from our models that Mars' core contains a median of 20 to 22 wt% light alloying elements when we consider sulfur, oxygen, carbon, and hydrogen. These data can be used to inform models of planetary accretion, composition, and evolution. [ABSTRACT FROM AUTHOR]

Constraining the thermal and compositional state of the mantle is crucial for deciphering the formation and evolution of Mars. Mineral physics predicts that Mars’ deep mantle is demarcated by a seismic discontinuity arising from the pressureinduced phase transformation of the mineral olivine to its higher-pressure polymorphs, making the depth of this boundary sensitive to both mantle temperature and composition. Here, we report on the seismic detection of a midmantle discontinuity using the data collected by NASA’s InSight Mission to Mars that matches the expected depth and sharpness of the postolivine transition. In five teleseismic events, we observed triplicated P and S waves and constrained the depth of this discontinuity to be 1,006 ± 40 km by modeling the triplicated waveforms. From this depth range, we infer a mantle potential temperature of 1,605 ± 100 K, a result consistent with a crust that is 10 to 15 times more enriched in heat-producing elements than the underlying mantle. Our waveform fits to the data indicate a broad gradient across the boundary, implying that the Martian mantle is more enriched in iron compared to Earth. Through modeling of thermochemical evolution of Mars, we observe that only two out of the five proposed composition models are compatible with the observed boundary depth. Our geodynamic simulations suggest that the Martian mantle was relatively cold 4.5 Gyr ago (1,720 to 1,860 K) and are consistent with a present-day surface heat flow of 21 to 24 mW/m². [ABSTRACT FROM AUTHOR]

Records of solar array currents recorded by the InSight lander during its first 200 sols on Mars are presented. In addition to the geometric variation in illumination on seasonal and diurnal timescales, the data are influenced by dust suspended in the atmosphere and deposited on the solar panels. Although no dust devils have been detected by InSight's cameras, brief excursions in solar array currents suggest that at least some of the vortices detected by transient pressure drops are accompanied by dust. A step increase in array output (i.e., a "cleaning event") was observed to be directly associated with the passage of a strong vortex. Some quasiperiodic variations in solar array current are suggestive of dust variations in the planetary boundary layer. Nonzero array outputs before sunrise and after sunset are indicative of scattering in the atmosphere: A notable increase in evening twilight currents is observed associated with noctilucent clouds, likely of water or carbon dioxide ice. Finally, although the observations are intermittent (typically a few hours per sol) and at a modest sample rate (one to two samples per minute), three single‐sample light dips are seen associated with Phobos eclipses. These results demonstrate that engineering data from solar arrays provide valuable scientific situational awareness of the Martian environment. Key Points: Solar array current telemetry gives situational awareness of the Mars surface environmentDust in the atmosphere is observed to varyTwilight currents indicate clouds [ABSTRACT FROM AUTHOR]

Seismic observations of impacts on Mars indicate a higher impact flux than previously measured. Using six confirmed seismic impact detections near the NASA InSight lander and two distant large impacts, we calculate appropriate scalings to compare these rates with lunar-based chronology models. We also update the impact rate from orbital observations using the most recent catalog of new craters on Mars. The snapshot of the current impact rate at Mars recorded seismically is higher than that found using orbital detections alone. The measured rates differ between a factor of 2 and 10, depending on the diameter, although the sample size of seismically detected impacts is small. The close timing of the two largest new impacts found on Mars in the past few decades indicates either a heightened impact rate or a low-probability temporal coincidence, perhaps representing recent fragmentation of a parent body. We conclude that seismic methods of detecting current impacts offer a more complete dataset than orbital imaging. [ABSTRACT FROM AUTHOR]

The InSight spacecraft landed successfully on Mars on November 26, 2018 at 4.50°N, 135.62°E. A large number of color images from an arm-mounted camera, including stereo coverage at two resolutions of the instrument deployment workspace and a 290° panorama (320° to 250° azimuth), provide information on the geology of the landing site. The lander is located within a degraded impact crater, dubbed Homestead hollow, with a smooth surface adjacent to a slightly rougher terrain with rocky ejecta craters nearby. The near surface is characterized by 1-10 m diameter impact craters in various stages of degradation, partly associated with eolian bedforms. Some like Homestead hollow have very little relief and are filled with fine-grained material. Farther afield, bright circular patches suggest soil-filled craters are common. No bedrock has been observed. The surface of Homestead hollow is made of smooth plains with low rock abundance (~2%), and the re-solvable particle size distribution is dominated by pebbles with slightly buried cobbles. Cobble and pebble shape and form are equant to sub-equant and angular to sub-angular, respectively, consistent with an origin via fragmentation. Some of the clasts closest to the lander have a dark grey color and appear aphanitic, consistent with fine-grained, dark mafic rocks (basalts). Other clasts appear lighter in albedo as if covered by dust and/or weathering rinds. At least one rock appears fluted, suggesting eolian abrasion (ventifact).Post-landing HiRISE images show a dark spot centered on the lander. In the workspace nearest the lander, the surface appears scoured, with multi-millimeter-relief ridges and troughs that extend radially from the lander. Some pebbles and protrusions have what appear to be wind tails that extend radially away from the lander. At least one rounded rock rolled across the surface creating divots and elongated depressions. These observations are consistent with the pulsed-descent motor exhaust removing surficial dust and granules to create the dark spot, as well as sculpting loose sand to create the scours and moving some pebbles.Three 10-20 cm-deep pits excavated by the retrorockets beneath the lander provide clues to the near surface structure. In one pit, the subsurface material is poorly sorted with pebbles and cobbles. Another pit has a steep slope (greater than the angle of repose) composed of small clasts and pebbles cemented in a finer-grained matrix (duricrust). Two footpads show evidence for slight sliding into place, creating a depression on one side and bulge in the direction of travel. These observations suggest a near surface stratigraphy of surficial dust over thin cohesionless sand, lying over a variable thickness (centimeters) duricrust, underlain by poorly sorted, cohesionless sand and clasts. Orbital thermal inertia measurements are consistent with a surface dominated by sand-sized particles, consistent with the cohesionless fines and the low rock abundance.In summary, the observations are consistent with a surface formed dominantly by impact, mass wasting, and eolian processes that created an impact-generated regolith composed dominatly of sand-sized particles with decreasing abundance of pebbles, cobbles and boulders, consistent with expectations established from remote sensing data prior to landing. [ABSTRACT FROM AUTHOR]