Convective vortices (whirlwinds) and dust devils (dust-loaded vortices) are one of the most common phenomena on Mars, observable on a daily basis. They reflect the local thermodynamical structure of the atmosphere and are the driving force of the dust cycle. Additionally, they cause an elastic ground deformation, which is useful for retrieving the subsurface rigidity. Therefore, investigating Martian convective vortices with the right instrumentation can lead to a better understanding of the Martian atmospheric structures as well as the subsurface physical properties. In this study, we quantitatively characterized the convective vortices detected by NASA’s InSight mission (~13,000 events) using both meteorological (e.g., pressure, wind speed, temperature) and seismic data. The evaluated parameters, such as the signal-to-noise ratio, event duration, asymmetricity of pressure drop profiles, and cross-correlation coefficient between seismic and pressure signals, are compiled as a catalog. To demonstrate how our catalog can contribute to scientific investigations, we show two analysis results about (i) asymmetrical features seen in the vortex-related pressure drops and (ii) atmospheric-ground interaction to retrieve the subsurface physical properties.

A document by Antoine Lucas. Click on the document to view its contents.

A document by Antoine Lucas. Click on the document to view its contents.

Titan is a prime target for astrobiological research. Organic materials from atmospheric chemistry precipitate on the surface and are subject to geological processes (e.g. eolian and fluvial erosion) that lead to the formation of dune fields, river networks and seas similar to their terrestrial counterparts. The analysis of the surface reflectance in the near-infrared (NIR) allows to constrain the surface composition, which is crucial to understand these atmosphere/surface interactions. However, Titan’s atmosphere prevents the surface from being probed in the NIR, except in 7 transmission windows where the methane absorption is sufficiently low (centered at 0.93, 1.08, 1.27, 1.59, 2.01, 2.7- 2.8 and 5 μm). We use an updated version of the Radiative Transfer (RT) model of Hirtzig et al. (2013), with updated gases and aerosols opacities, in order to better simulate atmospheric absorption and scattering and retrieve surface albedos in the 7 NIR transmission windows with an enhanced accuracy. Our RT model is based on the SHDOMPP and CDISORT (Evans, 2007 and Buras, 2011) solvers to solve the RT equations in plane-parallel and pseudo-spherical approximations respectively. We recently improved atmospheric inputs of the model with up-to-date gaseous CH4, CH3D, 13CH4, C2H2, HCN and CO abundances profiles and absorption coefficients (Vinatier et al. 2007, Niemann et al. 2010; Maltagliati et al. 2015; Serigano et al. 2016; Rey et al. 2018; Thelen et al. 2019; Gautier et al. 2021), and improved aerosol optical properties. In particular, optical properties of Titan’s aerosols are now computed from a fractal aggregate model (Rannou et al. 2003) constrained by measurements of the Huygens probe (Tomasko et al. 2008 and Doose et al. 2016). The new version of our RT model is benchmarked with the help of the most recent RT model for Titan (Coutelier et al. 2021) and validated using observations of the Descent Imager/Spectral Radiometer (DISR) onboard Huygens. Coupled with an efficient inversion scheme, our model can be apply to the Cassini’s Visual and Infrared Mapping Spectrometer (VIMS) dataset to retrieve atmospheric opacity and surface albedos at regional and global scales. This will help to analyze future James Webb Space Telescope (JWST) observations of Titan (Nixon et al. 2016) and prepare the Dragonfly mission (Lorenz et al. 2018).

The NASA InSight mission to Mars successfully landed on November 26th, 2018 in Elysium Planitia. It aims to characterize the seismic activity and constrain the internal structure of Mars. We focus on the Cerberus Fossae region, a giant fracture network of ~1200 km long situated east of the InSight landing site, and where M~3 marsquakes were detected during the past two years. It is formed of five main fossae located on the southeast of the Elysium Mons volcanic rise. We perform a detailed mapping of the entire system based on high resolution satellite images and Digital Elevation Models. The refined cartography reveals a range of morphologies associated with dike activities at depth. Width and throw measurements of the fossae are linearly correlated, suggesting a possible tectonic control on the shapes of the fossae. Widths and throws decrease toward the east, indicating the long-term direction of propagation of the dike-induced graben system. They also give insights into the geometry at depth and how the possible faults and fractures are rooted in the crust. The exceptional preservation of the fossae allows us to detect up to four scales of segmentation, each formed by a similar number of 3-4 segments/subsegments. This generic distribution is comparable to continental faults and fractures on Earth. We anticipate higher stress and potential for marsquakes within intersegment zones and at graben tips.

Mapping Titan’s surface albedo is a necessary step to give reliable constraints on its composition. However, even after the end of the Cassini mission, surface albedo maps of Titan, especially over large regions, are still very rare, the surface windows being strongly affected by atmospheric contributions (absorption, scattering). A full radiative transfer model is an essential tool to remove these effects, but too time-consuming to treat systematically the ~50000 hyperspectral images VIMS acquired since the beginning of the mission. We developed a massive inversion of VIMS data based on lookup tables computed from a state-of-the-art radiative transfer model in pseudo-spherical geometry, updated with new aerosol properties coming from our analysis of observations acquired recently by VIMS (solar occultations and emission phase curves). Once the physical properties of gases, aerosols and surface are fixed, the lookup tables are built for the remaining free parameters: the incidence, emergence and azimuth angles, given by navigation; and two products (the aerosol opacity and the surface albedo at all wavelengths). The lookup table grid was carefully selected after thorough testing. The data inversion on these pre-computed spectra (opportunely interpolated) is more than 1000 times faster than recalling the full radiative transfer at each minimization step. We present here the results from selected flybys. We invert mosaics composed by couples of flybys observing the same area at two different times. The composite albedo maps do not show significant discontinuities in any of the surface windows, suggesting a robust correction of the effects of the geometry (and thus the aerosols) on the observations. Maps of aerosol and albedo uncertainties are also provided, along with absolute errors. We are thus able to provide reliable surface albedo maps at pixel scale for entire regions of Titan and for the whole VIMS spectral range.

Orbital and surface observations demonstrate that aeolian activity is occurring on Mars. Here we report the aeolian changes observed in situ by NASA's InSight lander during the first 400 sols of operations. Aeolian changes include creep of grains with diameters of up to 3 mm, dust removal, dark trails left by passing vortices and possible saltation. InSight has observed such changes by using, for the first time, simultaneous imaging and continuous, high-frequency meteorological, seismological, and magnetic measurements. We show that this multi-instrument combination constrains both the timing, and specific atmospheric conditions during which, aeolian changes occur. The observed changes are infrequent and episodic, consistently occur between noon and 3 pm, and are systematically associated with the passage of convective vortices. The sudden onset of peak vortex wind speeds promotes particle motion during sequences of enhanced vortex activity and stronger ambient winds. Aeolian changes are correlated with excursions in ground acceleration and magnetic field strength, suggesting vortex-induced ground deformation and charged-particle motion.