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The 'two-box model' of planetary climate is discussed. This model has been used to demonstrate consistency of the equator-pole temperature gradient on Earth, Mars and Titan with what would be predicted from a principle of maximum entropy production (MEP). While useful for exposition and for generating first-order estimates of planetary heat transports, it has too low a resolution to investigate climate systems with strong feedbacks. A two-box MEP model agrees well with the observed day : night temperature contrast observed on the extrasolar planet HD 189733b.

Convective vortices (whirlwinds) and dust devils (dust‐loaded vortices) are one of the most common phenomena on Mars. 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 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 (∼13,000 events) using 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 between seismic and pressure signals, are compiled as a catalog. Using these parameters, we investigated (a) the vortex structure and (b) the subsurface physical properties. Regarding the first topic, we tried to illustrate the vertical vortex structure and its link to the shape of the pressure profiles by combining the asymmetrical features seen in the observed pressure drops and the terrestrial observations of dust devils. Our results indicate that most of the vortices move with the wall tilted in the advection direction. Concerning the second topic, selecting the highly correlated events between pressure perturbation and ground response, we estimated the subsurface rigidity at the InSight landing site down to 100 m depth. Our results indicate that the subsurface structure can be modeled with two layers having a transition at 5–15 m depth. Plain Language Summary: As frequently observed on Earth, convective vortices or dust‐loaded vortices are also seen on Mars. They reflect the local atmospheric structure and are the main driving force to lift the fine dust from the ground. In 2018, NASA's InSight succeeded in installing the meteorological and geophysical packages on Mars. That brought us, in particular, meteorological data with an extremely high temporal resolution, contributing to resolving local phenomena such as convective vortices. In this study, using InSight's meteorological (e.g., pressure, air temperature) and seismic data, we quantitatively characterize convective vortices to understand this phenomenon from both meteorological and geophysical aspects. Especially focusing on the asymmetricity of pressure drop profiles at vortex encounters and the correlation between the pressure variations and seismic signals, we investigated (a) a link between the shape of pressure drop profiles and the vertical vortex structure and (b) the ground rigidity structure by measuring the ground responses against the vortex‐related pressure variations. Consequently, first, we found that most of the vortices move with the wall tilted in the advection direction. Second, our results indicated that the subsurface structure can be modeled with two layers down to 100 m with a transition at 5–15 m depth. Key Points: We quantitatively characterized the Martian convective vortices observed by InSight's seismometer and meteorological instrumentsFocusing on the pressure drop profiles, we inferred a link between the asymmetricity and the vertical vortex structureWith the cataloged parameters, we performed a compliance analysis and evaluated the ground rigidity at the InSight landing site [ABSTRACT FROM AUTHOR]

We utilize SuperCam's Mars microphone to provide information on wind speed and turbulence at high frequencies on Mars. To do so, we first demonstrate the sensitivity of the microphone signal level to wind speed, yielding a power law dependence. We then show the relationship between the microphone signal level and pressure, air and ground temperatures. A calibration function is constructed using Gaussian process regression (a machine learning technique) taking the microphone signal and air temperature as inputs to produce an estimate of the wind speed. This provides a high rate wind speed estimate on Mars, with a sample every 0.01 s. As a result, we determine the fast fluctuations of the wind at Jezero crater which highlights the nature of wind gusts over the Martian day. To analyze the turbulent behavior of this wind speed estimate, we calculate its normalized standard deviation, known as gustiness. To characterize the behavior of this high frequency turbulent intensity at Jezero crater, correlations are shown between the evaluated gustiness statistic and pressure drop rates/sizes, temperature and energy fluxes. This has implications for future atmospheric models on Mars, taking into account turbulence at the finest scales. Plain Language Summary: The NASA Perseverance mission sent microphones to the surface of Mars. This microphone has recorded signals due to the wind. We examine how these recorded signals vary with other sensor data from Perseverance, which shows a link between the microphone signal, the dedicated wind speed sensor and air temperature. Based on this finding, we develop a way to predict the wind speed from the microphone data using a machine learning technique. The microphone records data at a very high rate compared with sensors so far sent to Mars. This means that the wind speed predicted from the microphone data can be used to study the chaotic and variable wind behavior on Mars to a level never seen before. We show that this chaotic and variable behavior has links to temperature and the number of whirlwinds observed. This will lead us to better weather models for Mars. Key Points: Wind‐induced noise is observed by the SuperCam Mars microphone on PerseveranceMicrophone and air temperature data are used to estimate the wind speed at high frequencies, using a machine learning modelThe wind speed estimate is used to examine the relationships between turbulent intensity, pressure drops, temperature, and energy flux [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]

Dust devils are likely the dominant source of dust for the martian atmosphere, but the amount and frequency of dust-lifting depend on the statistical distribution of dust devil parameters. Dust devils exhibit pressure perturbations and, if they pass near a barometric sensor, they may register as a discernible dip in a pressure time-series. Leveraging this fact, several surveys using barometric sensors on landed spacecraft have revealed dust devil structures and occurrence rates. However powerful they are, though, such surveys suffer from non-trivial biases that skew the inferred dust devil properties. For example, such surveys are most sensitive to dust devils with the widest and deepest pressure profiles, but the recovered profiles will be distorted, broader and shallow than the actual profiles. In addition, such surveys often do not provide wind speed measurements alongside the pressure time series, and so the durations of the dust devil signals in the time series cannot be directly converted to profile widths. Fortunately, simple statistical and geometric considerations can de-bias these surveys, allowing conversion of the duration of dust devil signals into physical widths, given only a distribution of likely translation velocities, and the recovery of the underlying distributions of physical parameters. In this study, we develop a scheme for de-biasing such surveys. Applying our model to an in-situ survey using data from the Phoenix lander suggests a larger dust flux and a dust devil occurrence rate about ten times larger than previously inferred. Comparing our results to dust devil track surveys suggests only about one in five low-pressure cells lifts sufficient dust to leave a visible track. [ABSTRACT FROM AUTHOR]

Abstract: In a survey of dust devil activity at a desert playa using continuous monitoring by a pressure logger, we have detected a number of pressure drops with complex structures: simple and symmetric drops make up only 25–30% of the total. In contrast to the simple, symmetric single-dip profiles expected for single-cell vertical vortices gliding past the pressure sensor, many profiles have an asymmetric shape, double dips, or ‘shoulders’ where a broad shallow dip is superposed on a narrow deeper one. A double dip in Mars Phoenix data was attributed in prior work to a near-simultaneous encounter with two dust devils, while laboratory experiments with two-cell vortices find a local peak in pressure at the center, also yielding a double dip in a transect profile. However, we suggest instead that a likely explanation for many complex pressure profiles measured in the field and on Mars is in fact the trochoidal path of a dust devil across the terrain, rather than the straight-line constant-speed path usually assumed. Images of the Martian surface show that many dust devil tracks have such a trochoidal or cycloidal path, which can be parametrically described. A model of the pressure profile driven by this parametric path description can reproduce observations. [Copyright &y& Elsevier]

Abstract: The amplitudes of seismic signals on a planetary surface are discussed in the context of observable physical quantities – displacement, velocity and acceleration – in order to assess the number of events that a sensor with a given detection threshold may capture in a given period. Spacecraft engineers are generally unfamiliar with expected quantities or the language used to describe them, and seismologists are rarely presented with the challenges of accommodation of instrumentation on spacecraft. This paper attempts to bridge this gap, so that the feasibility of attaining seismology objectives on future missions – and in particular, a long-lived Venus lander – can be rationally assessed. For seismometers on planetary landers, the background noise due to wind or lander systems is likely to be a stronger limitation on the effective detection threshold than is the instrument sensitivity itself, and terrestrial data on vehicle noise is assessed in this context. We apply these considerations to investigate scenarios for a long-lived Venus lander mission, which may require a mechanical cooler powered by a Stirling generator. We also consider wind noise: the case for decoupling of a seismometer from a lander is strong on bodies with atmospheres, as is the case for shielding the instrument from wind loads. However, since the atmosphere acts on the elastic ground as well as directly on instruments, the case for deep burial is not strong, but it is important that windspeed and pressure be documented by adequate meteorology measurements. [Copyright &y& Elsevier]

Abstract: Data from the Pathfinder and Phoenix landers on Mars show transient pressure drops (∼1–4 per day) attributed to nearby encounters with dust devils or dust-free vortices. The distribution of pressure drop amplitudes is consistent with a truncated power law distribution with a slope of −2, similar to that suggested previously for the optical diameters of dust devils. Comparable data from terrestrial field observations are very sparse: the only published dataset is half a century old and lists only 19 pressure drops. That dataset is too small to permit a robust comparison with Mars and likely suffers from a low detection efficiency at small dust devil sizes. Observed pressure drops in these fixed-station Mars datasets (30–300μbar) are 10× lower than those typically observed on Earth (0.3–3mbar): some higher drops have been reported for large terrestrial devils sampled by pursuing vehicles. The needed terrestrial data for comparison with Mars in-situ data (soon to be augmented, we hope, by the Mars Science Laboratory mission) is noted. Prospects for obtaining such data via field campaigns using new data acquisition technology, and with microbarographs for nuclear test monitoring, are discussed. [Copyright &y& Elsevier]

Abstract: Penetrators, which emplace scientific instrumentation by high-speed impact into a planetary surface, have been advocated as an alternative to soft-landers for some four decades. However, such vehicles have yet to fly successfully. This paper reviews in detail, the origins of penetrators in the military arena, and the various planetary penetrator mission concepts that have been proposed, built and flown. From the very limited data available, penetrator developments alone (without delivery to the planet) have required ∼$30M: extensive analytical instrumentation may easily double this. Because the success of emplacement and operation depends inevitably on uncontrollable aspects of the target environment, unattractive failure probabilities for individual vehicles must be tolerated that are higher than the typical ‘3-sigma’ (99.5%) values typical for spacecraft. The two pathways to programmatic success, neither of which are likely in an austere financial environment, are a lucky flight as a ‘piggyback’ mission or technology demonstration, or with a substantial and unprecedented investment to launch a scientific (e.g. seismic) network mission with a large number of vehicles such that a number of terrain-induced failures can be tolerated. [Copyright &y& Elsevier]

Abstract: We describe for the first time the generation and measurement of capillary waves in a water surface in a wind tunnel running with air at pressures of 15–1000 mbar. These experiments suggest a stronger dependence of wave generation on atmospheric density than the simple proportionality that might be expected from energy transfer arguments. Additionally, airflow over a nonaqueous fluid (kerosene) was found to produce waves of higher amplitude than for water under the same conditions. These preliminary results may indicate different efficiencies of wave generation on other planets, for which empirical terrestrial relations therefore do not apply, and thus may have a bearing on the lack of strong shoreline features on Mars and the possibility of specular glints from hydrocarbon lakes on Titan. [Copyright &y& Elsevier]

The degradation in electrical output of solar arrays on Mars landers and rovers is reviewed. A loss of 0.2% per Sol is typical, although observed rates of decrease in 'dust factor' vary between 0.05% and 2% per Sol. 0.2%/Sol has been observed throughout the first 800 Sols of the ongoing InSight mission, as well as the shorter Mars Pathfinder and Phoenix missions. This rate was also evident for much of the Spirit and Opportunity missions, but the degradation there was episodically reversed by cleaning events due to dust devils and gusts. The enduring success of those rover missions may have given an impression of the long-term viability of solar power on the Martian surface that is not globally-applicable: the occurrence of cleaning events with an operationally-useful frequency seems contingent upon local meteorological circumstances. The conditions for significant cleaning events have apparently not been realized at the InSight landing site, where, notably, dust devils have not been detected in imaging. Optical obscuration by dust deposition and removal has also been observed by ultraviolet sensors on Curiosity, with a similar (but slightly higher) degradation rate. The observations are compared with global circulation model (GCM) results: these predict a geographically somewhat uniform dust deposition rate, while there is some indication that the locations where cleaning events were more frequent may be associated with weaker background winds and a deeper planetary boundary layer. The conventional Dust Devil Activity metric in GCMs does not effectively predict the different dust histories. • Presents solar array dust factor evolution for 6 landed missions. • Evaluates statistics of solar array output decline, typically 0.2%/Sol but ranging 0.05–2%/Sol. • Determines statistics of cleaning events. • Compares evolution with meteorological predictions at the different landing sites. [ABSTRACT FROM AUTHOR]

Using rotorcraft to explore extraterrestrial bodies will allow future missions to explore terrain that is inaccessible to traditional lander/rover missions, and will enable spacecraft to explore much larger distances than previous missions. The upcoming Mars 2020 Rover mission will include the Mars Helicopter (named Ingenuity), a small (< 2 kg) counter-rotating co-axial vehicle, which, if successful, will be the first rotorcraft to fly on a non-terrestrial body. The Dragonfly mission, recently selected through the NASA New Frontier's program, is expected to fly a much larger vehicle on Titan (∼ 750 kg) arriving in the early 2030s. On Earth it is commonly observed that both sub-scale and full-scale rotorcraft can mobilize sediment, to varying degrees of magnitude, when a vehicle is operating over regolith. In order to determine the feasibility of performing sediment mobilization experiments (e.g. saltation investigations) beneath a rotorcraft through intentional sediment mobilization (due to the wake produced by the rotating rotors) for future missions, the scaling of aerodynamic and aeolian parameters should be accounted for. Furthermore, in an extreme case, this analysis can also be used as a low-fidelity method to begin to understand any potential risk associated with brownout (large-scale sediment mobilization due to the helicopter rotor wake) to the rotorcraft itself. In this work, a scaling analysis is presented that allows a vehicle designer to quickly investigate the magnitude of sediment mobilization beneath a rotorcraft, without requiring detailed CFD simulations. The analysis confirms that the upcoming Mars Helicopter and Dragonfly missions could be used for sediment mobilization experiments. [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]

Abstract: Estimates from visual surveys of the frequency of dust devils, even at terrestrial localities known for their abundance, vary by some four orders of magnitude, making a quantitative hazard assessment difficult. Here I show (1) that new high-quality observations from Mars fit a power law size distribution, (2) that such a power law population can unify the discrepant terrestrial surveys, and (3) that the populations on the two planets appear similar. [Copyright &y& Elsevier]

Dust devils are one of the most effective phenomena able to inject dust grains into the atmosphere. On Mars, they play an important role to maintain the haze and can significantly affect the global dust loading, especially outside the dust storm season. Despite dust devils having been studied for a century and a half, many open questions regarding their physics still exist. In particular, the nature of the dust lifting mechanisms inside the vortices, the development of the induced electric field and the exact contribution to the global atmospheric dust budget are still debated topics. In this paper, we analyze the dust devil activity observed in the Moroccan Sahara desert during a 2014 field campaign. We have acquired the most comprehensive field data set presently available for the dust devils: including meteorological, atmospheric electric field and lifted dust concentration measurements. We focus our attention on the electric field induced by vortices, using this as the principal detection parameter. We present, for the first time, the statistical distribution of dust devil electric field and its relationships with the pressure drop, the horizontal and vertical vortex velocity and the total dust mass lifted. We also compare the pressure drop distribution of our sample with the ones observed on the martian surface showing the similarity of the dust devils samples and the usefulness of this study for the next martian surface missions. [ABSTRACT FROM AUTHOR]

Acoustics has become extraterrestrial and Mars provides a new natural laboratory for testing sound propagation models compared to those ones on Earth. Owing to the unique combination of a microphone and two sound sources, the Ingenuity helicopter and the SuperCam laser-induced sparks, the Mars 2020 Perseverance rover payload enables the in situ characterization of unique sound propagation properties of the low-pressure CO 2 -dominated Mars atmosphere. In this study, we show that atmospheric turbulence is responsible for a large variability in the sound amplitudes from laser-induced sparks. This variability follows the diurnal pattern of turbulence. In addition, acoustic measurements acquired over one Martian year reveal a variation of the sound intensity by a factor of 1.8 from a constant source due to the seasonal cycle of pressure and temperature that significantly modifies the acoustic impedance and shock-wave formation. Finally, we show that the evolution of the Ingenuity tones and laser spark amplitudes with distance is consistent with one of the existing sound absorption models, which is a key parameter for numerical simulations applied to geophysical experiments on CO 2 -rich atmospheres. Overall, these results demonstrate the potential of sound propagation to interrogate the Mars environment and will therefore help in the design of future acoustic-based experiments for Mars or other planetary atmospheres such as Venus and Titan. • A microphone and two sound sources are used to study sound propagation on Mars. • Atmospheric turbulence scatters the acoustic signals recorded on Mars. • The amplitude scattering follows the daytime turbulence pattern. • Sounds intensity varies by a factor of 1.8 over a Martian year. • The sound amplitude evolution with distance matches with the sound attenuation model. [ABSTRACT FROM AUTHOR]

The NASA InSight lander has recorded many pressure drops attributed to convective vortices during its first full year of data collection. However, although dust-carrying vortices (dust devils) are a common phenomenon on Mars, they have not been observed in InSight images. On Earth, magnetic signals associated with some dust devils have been reported. Data from the InSight Fluxgate Magnetometer (IFG) provide the first opportunity for similar investigations on Mars. Here, we evaluate whether magnetic signals are associated with daytime vortices. We incorporate observations of environmental conditions, measurements of ground tilt from seismic data, and data from the lander's solar panels, and consider the potential for dust-laden vortices to generate observable magnetic field signals. We find that 7.7% of pressure drop events greater than 1 ​Pa show a resolvable magnetic field signal at the time of the pressure drops. The resolvable magnetic signals, typically seen on the horizontal field components, are less than 1 ​nT in amplitude, and have no clear correlation with local time, duration, or pressure drop magnitude. During nine pressure drop events we found smoothly varying magnetic signals of at least 0.3 ​nT on any one component. To investigate the origin of these magnetic signals we evaluated three possible sources: solar array currents (SAC), ground and lander tilt, and triboelectric effects of lofted dust. We find that SAC and tilt could contribute a change in the magnetic field but cannot solely explain the observed signals. The observed changes in field strength could theoretically be produced via triboelectric effects, but only in the case of exceptionally large dust devils that pass close to the lander. The lack of imaged dust devils and the small number of observed magnetic signatures despite numerous measured pressure drops is consistent with at most a small proportion of dust laden convective vortices at InSight and associated predicted triboelectric effects. • We investigate magnetic field signatures of vortices on Mars with InSight data. • 7.7% of 862 pressure drop events >1 ​Pa exhibit magnetic field signals < ∼1 ​nT. • Dust-laden convective vortices in close approach could cause magnetic field signals. • Most pressure drop events lack magnetic signals, matching dearth of dust devil images. [ABSTRACT FROM AUTHOR]