Martian Dust Devils Research Articles

Spectral location for the universal scaling regime in Martian atmospheric turbulence

Atmospheric turbulence, irregular fluctuations of the fluid state, is studied on Mars. Universality of the turbulence spectrum underpins atmospheric models where computational requirements preclude full fidelity simulations of the smallest scales. However, there are discrepancies among reports on the existence and spectral location of universal scaling in Martian atmospheric data. Here, results indicate the smallest resolvable structures from Martian wind speed data are still associated with the energetic regime, which may ultimately explain why multiple reports have not found a consistent Kolmogorov-like spectral regime on Mars. Universal spectral scaling of wind data from Perseverance’s Mars Environmental Dynamics Analyzer is used to estimate the thresholds that separate three turbulence regimes: energetic, inertial, and molecular dissipation. Wind measurements at 2-Hz, the fastest sampling rate for direct wind sensor measurements on Mars, resolves turbulence in the energetic regime and approaches the inertial regime, which is consistent with reported Martian dust devil sizes.

First quantitative characterization of the Martian dust devil dimensions determined from InSight data

In a pioneer study, the dimensions height H and width D of Martian dust devils are determined considering a simple model, in which the principal contribution to the magnetic field generated by a dust devil, comes from the swirling motion of their negatively charged lighter particles. Finally, a linear relation between H/D and the pressure drop associate to the dust devils is found. This relationship is a new and very conspicuous result determined in the present study. The reliability of this result should be assured revisiting this work with the data provided by future missions, as the Exobiology on Mars (ExoMars) project, when these data sets be available.

Novel design of multi-point injection system for laboratory simulation of Martian low-pressure dust devils

The Martian surface is frequently traversed by dust devils, presenting formidable challenges to exploration missions and posing significant safety risks. Establishing a ground-based simulation device for low-pressure Martian dust devils is essential for conducting reliability testing and research on extreme environments relevant to Mars rovers. This study introduces a Martian dust devil simulator comprising a simulation cabin and multi-point injectors. This apparatus facilitates the investigation of velocity and pressure distribution patterns within the flow field under varying operational conditions by adjusting injector positions, inlet pressure, and internal pressure. The simulator's design allows it to replicate Martian dust devil velocity fluctuations from 0 to 50 m/s and pressure variations spanning 100–1500 Pa, thereby meeting crucial criteria for simulating Martian atmospheric conditions. Through computational fluid dynamics (CFD) simulation, we analyzed the characteristics of dust devils generated by the simulation device and scrutinized the flow field properties following the coupling of sand-dust particles with airflow. The observed dust devil flow field closely resembles the Vastitas Borealis vortex. Additionally, experimental research was conducted. Comparing experimental, simulated, and theoretical models revealed a high degree of consistency in the internal flow field characteristics of the simulated dust devils. The apparatus's versatility extends to simulating various dust devil morphologies, offering significant potential for conducting model experiments pertinent to Martian probes and facilitating future crewed Mars exploration endeavors.

Martian Dust Devil Detection Based on Improved Faster R-CNN

Martian Dust Devil Detection Based on Improved Faster R-CNN

The sound of a Martian dust devil

Dust devils (convective vortices loaded with dust) are common at the surface of Mars, particularly at Jezero crater, the landing site of the Perseverance rover. They are indicators of atmospheric turbulence and are an important lifting mechanism for the Martian dust cycle. Improving our understanding of dust lifting and atmospheric transport is key for accurate simulation of the dust cycle and for the prediction of dust storms, in addition to being important for future space exploration as grain impacts are implicated in the degradation of hardware on the surface of Mars. Here we describe the sound of a Martian dust devil as recorded by the SuperCam instrument on the Perseverance rover. The dust devil encounter was also simultaneously imaged by the Perseverance rover’s Navigation Camera and observed by several sensors in the Mars Environmental Dynamics Analyzer instrument. Combining these unique multi-sensorial data with modelling, we show that the dust devil was around 25 m large, at least 118 m tall, and passed directly over the rover travelling at approximately 5 m s−1. Acoustic signals of grain impacts recorded during the vortex encounter provide quantitative information about the number density of particles in the vortex. The sound of a Martian dust devil was inaccessible until SuperCam microphone recordings. This chance dust devil encounter demonstrates the potential of acoustic data for resolving the rapid wind structure of the Martian atmosphere and for directly quantifying wind-blown grain fluxes on Mars.

Automated detection of dust-devil-induced pressure signatures

Dust devils are common on Mars and in Earth’s arid regions. On Mars, studying the dust devil population is important for understanding dust loading of the Martian climate and has important consequences for robotic and future human exploration. Studying dust devils on Mars is difficult due to insufficient spatio-temporal coverage. Our team is analyzing an infrasound dataset encompassing 7 years of data recorded at the Nevada Nuclear Security Site in the Mojave desert, to identify and characterize terrestrial dust devils as analogues for Martian dust devils. However, the size of this long-duration dataset mandates the use of automated techniques for the detection of dust devils.The automated detection scheme that we have developed follows a two-step process. The first step comprises of significance testing in the time-frequency domain using wavelet transforms and an empirical background red noise model. The second step is a correlation-based, template-matching detector, which utilizes the “heartbeat” pressure signal produced by the dust devil convolved with the microbarometer’s impulse response. In this presentation, we will discuss our automated dust devil detection algorithm, error characterization in the identification of signatures using Monte Carlo analysis and the application of the automated detector to the long-term monitoring dataset.

Numerical Simulation of Dust Lifting Within a Steady State Dust Devil

AbstractOn Mars, dust devils play an important role in injecting dust grains into the atmosphere. The exact amount that they contribute to the dust budget of the atmosphere is yet not clearly known. In this study, we model the spatial distribution of dust concentration within a steady state Martian dust devil for the first time. We numerically solve the equations of motion for dust particles to determine their velocity inside a dust devil, 10 m wide and 1,000 m tall, and consequently determine the dust loading using the continuity equation. We consider an initial wind profile, which is dependent on the circulation strength of the vortex (Γ) and viscosity of the air (ν). Our simulations indicate a maximum concentration of ∼1,400 cm−3 near the surface and at the boundary of the vortex. The larger size particles are lifted to lower heights. The radial and tangential particle velocities peak at ∼60 m, while the vertical velocity peaks at ∼100 m. A higher circulation strength (Γ), leads to a higher loading of dust, whereas a change in the air viscosity (ν) does not have a significant effect on the dust loading inside the steady state dust devil. From the simulated dust distribution in our vortex, the estimations of a dust flux of ∼5 × 10−5 kgm−2s−1, a total optical depth of 0.2 and a near‐surface heating rate of , are consistent with observations. Our calculations can provide useful inputs to study the effect of dust devils on boundary layer processes.

Detection of spark discharges in an agitated Mars dust simulant isolated from foreign surfaces

Numerous laboratory experiments, starting in the Viking Lander era, have reported that frictional interactions between Martian analog dust grains can catalyze electrostatic processes (i.e. triboelectrification). Such findings have been cited to suggest that Martian dust devils and dust storms may sustain lightning storms, glow discharges, and other complex electrostatic phenomena. However, in many cases (if not most), these experiments allowed Martian dust simulant grains to contact foreign surfaces (for instance, the wall of an environmental chamber or other chemically-dissimilar particles). A number of authors have noted that such interactions could produce charging that is not representative of processes occurring near the surface of Mars. More recently, experiments that have identified and corrected for collisions between dust simulants and chemically dissimilar laboratory materials have either failed to replicate near-surface Martian conditions or directly measure discharging. In this work, we experimentally characterize the triboelectrification of a Martian dust simulant resulting from both isolated particle–particle collisions and particle–wall collisions under a simulated Martian environment. We report the direct detection of spark discharges in a flow composed solely of natural basalt grains and isolated from artificial surfaces. The charge densities acquired by the fluidized grains are found to be of order 10-6 Cm-2 (in excess of the theoretical maximum charge density for the near-surface Martian environment). Additionally, we demonstrate that the interaction of simulant particles with experimental walls can modulate the polarity of spark discharges. Our work supports the idea that small-scale spark discharges may indeed be present in Martian granular flows and may be qualitatively similar to small-scale discharges in terrestrial volcanic vents.

Modelling martian dust devils using in-situ wind, pressure, and UV radiation measurements by Mars Science Laboratory

NASA's Mars Science Laboratory rover Curiosity (MSL) has measured simultaneous fluctuations in wind and atmospheric pressure caused by passing convective vortices, i.e. dustless dust devils. We study the dynamics of these vortices by fitting a mathematical vortex model to the wind and pressure measurements of MSL. The model matches the data adequately well in 29 out of the 33 studied vortex pass events having sufficient data quality. Clockwise and counterclockwise rotating directions are equally common among the studied convective vortices. The vortices seem to prefer certain trajectories, e.g. avoiding steep slopes. However, our results show that due to sensitivity constraints of the method, central pressure drops of Martian dust devils can usually not be accurately determined by fitting a theoretical vortex model to simultaneous pressure and wind measurements of a single station. We also present a methodology extension for further constraining the trajectories and the strengths of dust laden vortices (i.e. dust devils), based on concurrent in-situ solar irradiance measurements. We apply this methodology to the only evidently dust laden vortex in our data set and show that its dust lifting capacity is probably based not only on wind stress lifting.

Dust devils on Mars

Whirlwinds, familiar on Earth, can be informative probes of the Martian surface environment.

Lifting grains by the transient low pressure in a martian dust devil

Lifting dust and sand into the thin Martian atmosphere is a challenging problem. Atmospheric pressure excursions within dust devils have been proposed to support lifting. We verify this idea in laboratory experiments. Pressure differences up to a few Pa are applied along particle layers of 50 to 400 μm. As samples we used glass beads of ∼50 μm diameter and irregular basalt grains of ∼20 μm in size. The total ambient pressure of air was set to 600 Pa. Particles are ejected at pressure differences as low as 2.0 ± 0.8 Pa. In the case of glass beads, the ejected grains returning to the particle bed can trigger new particle ejections as they reduce cohesion and release the tension from other grains. Therefore, few impacting grains might be sufficient to sustain dust lifting in a dust devil at even lower pressure differences. Particle lift requires a very thin, ∼100 μm, low permeability particle layer on top of supporting ground with larger pore space. Assuming this, our experiments support the idea that pressure excursions in Martian dust devils release grains from the ground.

On the relationship between dust devil radii and heights

The influence of dust devils on the martian atmosphere depends on their capacity to loft dust, which depends on their wind profiles and footprint on the martian surface, i.e., on their radii, R. Previous work suggests the wind profile depends on a devil’s thermodynamic efficiency, which scales with its height, h. However, the precise mechanisms that set a dust devil’s radius have remained unclear. Combining previous work with simple assumptions about angular momentum conservation in dust devils predicts that R∝h1∕2, and a model fit to observed radii and heights from a survey of martian dust devils using the Mars Express High Resolution Stereo Camera agrees reasonably well with this prediction. Other observational tests involving additional, statistically robust dust devil surveys and field measurements may further elucidate these relationships.

On the statistical distribution of pressure drops in convective vortices: Applications to martian dust devils

A theoretical approach based on the Abel transform is proposed to infer the statistical distribution of the pressure drop in the center of convective vortices, including dust devils, based on measurements of peak pressure drops at a ground-based meteorological station, when the vortices pass over or near the barometric sensor. We show that if the pressure inside the vortex is modeled realistically, then the statistics of observed pressure drops is related to the statistics of pressure drops in vortex centers of the subpopulation of vortices detected by the pressure sensor. This relationship holds for an arbitrary size-frequency distribution of dust devils. The relationship between the observed statistics of pressure drops and the statistics of central pressure drop values for the whole population of vortices depends on the correlation between the dust-devil diameter (defined either optically or as twice the radius of the maximum circumferential velocity in the vortex) and the maximum pressure drop in its center. If the observed statistics can be approximated with a truncated power-law distribution then this approximating distribution is generally biased toward overestimation of the contribution from vortices with larger pressure drops. In a case of no apparent correlation between the vortex diameter and the maximum pressure drop in its center, the measurements provide an unbiased power-law estimate of the actual central pressure drop-frequency distribution. These theoretical results are applied to three sets of observations of Martian convective vortices, including dust devils.

Reaction: Chemistry Driven by the Harsh Space Environment

Dr. Bill Farrell is a plasma physicist at NASA's Goddard Space Flight Center. He is a co-investigator on the Cassini mission to Saturn and the Parker Solar Probe mission. He is also principal investigator of the DREAM2 Center for Space Environments (http://ssed.gsfc.nasa.gov/dream/), which examines the exosphere formation, radiation effects, and plasma interactions of the Moon and other airless bodies. Dr. Farrell has authored or co-authored over 200 journal articles on various aspects of space science, including the hydroxylation at the Moon, the curious plasma effects within the Enceladus plume, and the possibility of electricity generated in Martian dust devils.

Automatic detection of typical dust devils from Mars landscape images

This paper presents an improved algorithm for automatic detection of Martian dust devils that successfully extracts tiny bright dust devils and obscured large dust devils from two subtracted landscape images. These dust devils are frequently observed using visible cameras onboard landers or rovers. Nevertheless, previous research on automated detection of dust devils has not focused on these common types of dust devils, but on dust devils that appear on images to be irregularly bright and large. In this study, we detect these common dust devils automatically using two kinds of parameter sets for thresholding when binarizing subtracted images. We automatically extract dust devils from 266 images taken by the Spirit rover to evaluate our algorithm. Taking dust devils detected by visual inspection to be ground truth, the precision, recall and F-measure values are 0.77, 0.86, and 0.81, respectively.

To the theory of particle lifting by terrestrial and Martian dust devils

The combined Rankine vortex model is applied to describe the radial profile of azimuthal velocity in atmospheric dust devils, and a simplified model version is proposed of the turbulent surface boundary layer beneath the Rankine vortex periphery that corresponds to the potential vortex. Based on the results by Burggraf et al. (1971), it is accepted that the radial velocity near the ground in the potential vortex greatly exceeds the azimuthal velocity, which makes tractable the problem of the surface shear stress determination, including the case of the turbulent surface boundary layer. The constructed model explains exceeding the threshold shear velocity for aeolian transport in typical dust-devil vortices both on Earth and on Mars.

Lifting particles in martian dust devils by pressure excursions

The passage of a dust devil vortex goes along with a pressure reduction above ground. This leads to a sub-soil overpressure. It has been suggested that this enhances the lift on particles and facilitates dust entrainment by dust devils. We quantify the necessary pressure difference to lift fine sand from sand beds with thickness of 50, 150, and 250 mm in laboratory experiments with basalt samples consisting of 63–125 μm grains. The absolute pressure was varied between 1,300 and 3,600 Pa. In general, a pressure differences of about 30 Pa per mm depth is needed to lift sand grains. With slight systematic variations this is in agreement to simply accounting for the weight of a lifted particle layer. On Mars observed absolute pressure difference are several Pa. This limits particle lift to a layer smaller than 100 μm. However, it clearly allows Δp lifting if the top layer has a decreased permeability. This might be the case for dust layers sitting on top of a coarse grained sand bed. These measurements support the idea of enhanced dust entrainment due to the Δp-effect in Martian dust devils under certain conditions.

Modeling of Ground Deformation and Shallow Surface Waves Generated by Martian Dust Devils and Perspectives for Near-Surface Structure Inversion

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/s2 for rocky subsurface models and reaches 10–20 nm/s2 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.

The Martian dust devil electron avalanche: Laboratory measurements of the E-field fortifying effects of dust-electron absorption

Analogous to terrestrial dust devils, charged dust in Mars dust devils should become vertically stratified in the convective features, creating large scale E-fields. This E-field in a Martian-like atmosphere has been shown to stimulate the development of a Townsend discharge (electron avalanche) that acts to dissipate charge in regions where charge build-up occurs. While the stratification of the charged dust is a source of the electrical energy, the uncharged particulates in the dust population may absorb a portion of these avalanching electrons, thereby inhibiting dissipation and leading to the development of anomalously large E-field values. We performed a laboratory study that does indeed show the presence of enhanced E-field strengths between an anode and cathode when dust-absorbing filaments (acting as particulates) are placed in the avalanching electron flow. Further, the E-field threshold condition to create an impulsive spark discharge increases to larger values as more filaments are placed between the anode and cathode. We conclude that the spatially separated charged dust creates the charge centers and E-fields in a dust devil, but the under-charged portion of the population acts to reduce Townsend electron dissipation currents, further fortifying the development of larger-than-expected E-fields.

Diurnal variation in martian dust devil activity

We show that the dust devil parameterisation in use in most Mars Global Circulation Models (MGCMs) results in an unexpectedly high level of dust devil activity during morning hours.Prior expectations of the diurnal variation of Martian dust devils are based mainly upon the observed behaviour of terrestrial dust devils: i.e. that the majority occur during the afternoon. We instead find that large areas of the Martian surface experience dust devil activity during the morning in our MGCM, and that many locations experience a peak in dust devil activity before mid-sol.We find that the diurnal variation in dust devil activity is governed by near-surface wind speeds. Within the range of daylight hours, higher wind speeds tend to produce higher levels of dust devil activity, rather than the activity simply being governed by the availability of heat at the planet’s surface, which peaks in early afternoon.Evidence for whether the phenomenon we observe is real or an artefact of the parameterisation is inconclusive. We compare our results with surface-based observations of Martian dust devil timings and obtain a good match with the majority of surveys. We do not find a good match with orbital observations, which identify a diurnal distribution more closely matching that of terrestrial dust devils, but orbital observations have limited temporal coverage, biased towards the early afternoon.We propose that the generally accepted description of dust devil behaviour on Mars is incomplete, and that theories of dust devil formation may need to be modified specifically for the Martian environment. Further surveys of dust devil observations are required to support any such modifications. These surveys should include both surface and orbital observations, and the range of observations must encompass the full diurnal period and consider the wider meteorological context surrounding the observations.