Detecting seismic activity on Saturn's icy moon Titan during the Dragonfly mission could provide crucial information on its internal structure. The geological complexity of the moon's surface suggests significant cyclic tidal deformation, likely leading to the fracturing of the ice shell. Considering realistic source locations and fault geometries, we assess whether a vertical short-period seismometer can detect body waves from a 4.0 icequake. Signal-to-noise ratios are evaluated by comparing the high-frequency content with the expected background noise and instrument capabilities for several ice attenuation scenarios and 1D interior models. Our results indicate that the high-frequency content (Hz) of tidal-induced icequakes is likely undetectable under the most unfavorable attenuation scenarios and atmospheric conditions. However, seismic signals in the 0.5-1 Hz band-where P wave reflections dominate-may still be observable for events occurring in potential seismically active regions at similar to 800-1,000 km from the Dragonfly's landing site. These signals could provide constraints on the thickness of Titan's outer ice shell, provided that intrinsic attenuation is low and environmental conditions are favorable.

Mars is drying, yet how water is supplied to the free atmosphere during the escape season remains unresolved. Here we identify a southern mid-latitude storm corridor (15–40°S) that activates near perihelion, when radiative and dynamical conditions are most favourable for deep dust–water transfer. Across this belt, near-daily mesoscale storms—including a newly identified family of cyclones, from 10–30-km compact spirals with winds approaching 100 m s⁻¹ to >300-km vortices—repeatedly inject dust and water above the daytime boundary layer, feeding a recurrent seasonal band of enhanced water aloft. Individual storm injections can dominate the hemispheric day-to-day increase in water-ice loading up to 20 km altitude, showing that perihelion-season supply is organised primarily by episodic storm "chimneys" rather than diffuse ascent alone. Tracer simulations show that replenishment of high-altitude water is dominated by corridor injections, which are rapidly exported poleward and reach escape-relevant altitudes within days. Together, these results define a perihelion-gated pathway between near-surface reservoirs and the free atmosphere, coupling mesoscale weather to modern Martian desiccation.

The current effort presents novel investigations of rotor-wake–surface interactions for the Dragonfly lander, NASA's rotorcraft lander to explore Titan. The numerical framework couples unsteady RANS with blade-element and virtual disk rotor models and a coupled Lagrangian particle tracking method to examine rotor–ground interactions and brownout. Simulations span a range of complexity, from isolated rotor benchmarks and rotor pairs to full eight-rotor configurations without a fuselage and the eight-rotor configuration with a simplified Dragonfly fuselage. To quantify model fidelity and near-ground shear, blade-resolved simulations of the isolated rotor are performed using Spalart–Allmaras and Reynolds Stress turbulence models with vorticity confinement, demonstrating that virtual blade models under-predict tip-vortex strength and local inflow distortion but reproduce wall shear reasonably well, whereas blade-resolved RSM solutions yield higher peak shear levels relevant to brownout prediction. These findings improve understanding of planetary rotorcraft aeromechanics and sediment transport in ground-effect while supporting ongoing efforts to assess environmental risks for Dragonfly operations and inform multi-rotor VTOL design for terrestrial applications.

Turbulent winds are a regular occurrence in planetary boundary layers. Turbulence affects mixing, energy fluxes and forcing on the surface environment. Energy injected into an atmosphere generates eddies of many scales down to a size where molecular viscous forces dominate, termed the Kolmogorov length scale. Here, we present an analysis of the turbulent energy cascade at this scale, the transition between the inertial and dissipative regimes, for the first time on Mars. This analysis is based on data from the SuperCam microphone on the Perseverance mission. We find a distribution of power laws in the inertial regime predominantly between -3 and -1 and the distribution of the Kolmogorov length scale from 0.005 to 0.03 m. This yields estimates of the dissipation rate of turbulence between 0.0001 and 1 . We compare these values to those calculated using Monin-Obukhov similarity theory, identifying potential shortcomings for its application on Mars without modification.

Titan is an object of great interest in studying the chemical origins of life, but it is intensely cold and cannot support 'life as we know it': it is therefore designated a Planetary Protection Category II* target. Titan is thought to have an internal water ocean, but it is isolated beneath an approximately 100 km thick ice crust. Herein, the particulars of the Dragonfly rotorcraft lander mission and the Titan environment are reviewed, demonstrating that inoculation of the ocean with viable terrestrial biota by the mission is a very low-probability event (much less than 10-4), thereby consistent with a mission designation of Category II. This article is part of the theme issue 'Planetary Protection for sustainable space exploration'.

We used attitude data from the Mars Ingenuity helicopter with a simple steady-state model to estimate windspeeds and directions at altitudes of 3 meters up to 24 meters, the first time winds at such altitudes have been probed on Mars. We compared our estimates to concurrent wind data at 1.5 m height from the meteorology package MEDA onboard the Mars 2020 Perseverance rover and to predictions from meteorological models. Wind directions inferred from the Ingenuity data agreed to within uncertainties with the directions measured by MEDA, when the latter were available, but deviated from model-predicted directions by as much as 180 deg in some cases. Also, the inferred windspeeds are often much higher than expected. For example, meteorological predictions tailored to the time and location of Ingenuity's 59th flight suggest Ingenuity should not have seen windspeeds above about 15 m/s, but we inferred speeds reaching nearly 25 m/s. By contrast, the 61st flight was at a similar time and season and showed weaker winds then the 59th flight, suggesting winds shaped by transient phenomena. For flights during which we have MEDA data to compare to, inferred windspeeds imply friction velocities exceeding 1 m/s and roughness lengths of more than 10 cm based on a boundary layer model that incorporates convective instability, which seem implausibly large. These results suggest Ingenuity was probing winds sensitive to aerodynamic conditions hundreds of meters upwind instead of the conditions very near Mars 2020, but they may also reflect a need for updated boundary layer wind models. An improved model for Ingenuity's aerodynamic response that includes the effects of transient winds may also modify our results. In any case, the work here provides a foundation for exploration of planetary boundary layers using drones and suggests important future avenues for research and development.

A model of turbulence in the Venus atmosphere is developed for simulating the dynamics of vehicles such as balloons or descent probes, with particular application to the low-latitude daytime descent of the DAVINCI probe currently in development. A discrete ‘random-walk’ turbulence formulation of continuous gusts is used, which offers simple implementation for numerical flight simulations. The model is validated against Doppler observations of the Venera 11 and 12 landers and other data, and some features and challenges of interpreting models and observations are discussed. Model parameter variations as a function of latitude and local time are suggested.

Convective vortices, and their particle-laden counterparts dust devils, are an important feature of the meteorology of both Mars and terrestrial desert areas. In addition to being interesting phenomena in their own right, they can cause occasional damage and even death. The last 12 years has seen the generation of statistically-robust catalogs of vortex encounters from long-lived (>1000 Sol) landers and rovers equipped with meteorological instrumentation, namely MSL, InSight and Mars 2020. Although previous landers (Phoenix and Pathfinder, lasting ~100 Sols) yielded catalogs that were enough to indicate useful analytic function descriptions of vortex population functions (e.g. power laws or exponentials of number versus measured pressure drop), the new generation of missions provide much more robust statistics, and also have had more extensive instrumentation, permitting the documentation of wind speed, dust loading and even seismic characteristics of vortex encounters.In the 2000s, the Mars statistics were in fact rather better than those available for the Earth, but the advent of inexpensive and low-power data logging systems with flash memory permitted the long-duration (months) acquisition of high-cadence (>1/second) pressure and other data required to detect small vortices in unattended field measurement campaigns. Inexpensive timelapse cameras have also permitted optical surveys of dust devils that are comparable with those from Mars landed and orbital missions.In many respects the populations of vortex events are surprisingly similar on the two worlds, when expressed as a normalized peak pressure drop (pressure drop divided by ambient pressure : this quantity is proportional to the peak wind speed at the wall of the vortex). The cumulative rate of encounters typically varies as a power law with an exponent of about -2, and Martian rates are a factor of several higher than those on Earth. Although the convective heating rates of the respective surfaces are somewhat different, a key difference is that the Martian Planetary Boundary Layer, which sets the upper limit on vortex size, is much deeper, and Martian dust devils are typically larger than Earth’s as a result. I will review these population functions and their implications for meteorology, dust lifting and safety.

An extraterrestrial submarine was studied to explore Saturn's moon Titan, under a Phase II NASA Innovative Advanced Concepts (NIAC) study. One of the primary design concerns for the submarine is the effect of effervescence on submarine operation. Nitrogen gas is highly soluble in Titan's methane-rich sea, Ligeia Mare. Waste heat from the submarine power system may cause this dissolved nitrogen gas to come out of solution; in a quiescent case, bubbles that form may interfere with science instruments, and in a moving case, bubbles that form along the submarine may coalesce at the aft end and cause cavitation in the propellers. This paper introduces the Phase II orbiter-supported submarine, updated mission profile, critical subsystems, as well as relevant models needed to quantify effervescence as a function of the location and operation within Ligeia Mare. Phase I and Phase II submersible designs are also compared and contrasted.

As a phenomenon that occurs on Earth and on Mars, the diameter of a dust devil helps determine the amount of dust the devil injects into the atmosphere for both worlds—for a given dust flux density (dust lifted per area per time), a wider devil will lift more dust into the air. However, the factors that determine a dust devil’s diameter D and how it might relate to the ambient conditions have remained unclear. Moreover, estimating the contribution to an atmospheric dust budget from a population of dust devils with a range of diameters requires an accurate assessment of the differential diameter distribution, but considerable work has yet to reveal the best representation or explain its physical basis. In this study, we propose that this distribution follows a power law ∝ D ^−5/3 and provide a simple physical explanation for why the distribution takes this form. By fitting diameter distributions of Martian dust devil diameters reported in several studies, we show that the data from several studies support this proposed form. Using a previous model that treats dust devils as thermodynamic heat engines, we also show that the areal density of dust devils (number per unit area) N _0 scales with the product of their thermodynamic efficiency η and the sensible heat flux F _s as N _0 ∝ ηF _s .

Electrical discharges such as lightning are among the most energetic and remarkable phenomena in planetary atmospheres. Both laboratory experiments and modeling studies have predicted that triboelectric charging of wind-blown particles in dust events on Mars should lead to significant electrification. However, there have been no direct measurements of a Martian electric field or observations of discharges. Here, using acoustic recordings from the SuperCam microphone onboard the Perseverance rover, we report evidence for an atmospheric discharge in a dust devil, based on the electromagnetic and acoustic signatures observed in the microphone signal. This is the first direct detection of a triboelectric discharge in the Mars atmosphere. It shows that the electric field in a dust devil can reach 25 kV/m, which is the expected breakdown threshold of the Mars atmosphere. Electrical discharges on Mars may have implications for dust dynamics, the chemistry of oxidants and methane in the atmosphere, and ultimately robotic and human exploration.

Dust devils are dust‐raising atmospheric vortices that leave tracks of surface disturbance. In the first high‐resolution global survey of martian dust devil tracks (DDTs), we find them in 4% of High Resolution Imaging Science Experiment images 2014–2018. They are concentrated near ±60° latitude and peak in local summer, more frequently in the southern hemisphere summer (L S ∼ 250°–320°), coinciding with peak heating. DDT formation does not correlate with elevation, indicating it does not depend on ambient atmospheric pressure. Locations and timing of DDTs are similar to active dust devils, with several regional exceptions. DDTs are most common in areas characterized by low albedo and moderate thermal inertia, where thin layers of dust overlie larger‐grained material that provides an albedo contrast when uncovered by the passage of an atmospheric vortex. In addition to revealing the nature and formation of DDTs, this study has implications for solar‐powered exploration of Mars, identifying potential dust‐clearing event regions.

Dragonfly, NASA’s 4 th New Frontiers mission, is a radioisotope-powered rotorcraft arriving at Saturn’s moon Titan in the 2030s which carries several payloads to explore this organic-rich ocean world. Among these payloads is a Geophysics and Meteorology package (DraGMet) which hosts a variety sensors to observe the Titan environment. Among these is a set of microphones (MICRO) mounted around the rotorcraft. These microphones will provide situational awareness, diagnosing the health of Dragonfly’s rotors, fans, and drill. The experience with the microphones on Mars 2020 demonstrates powerful scientific discovery potential, with possible measurements including sound propagation (speed and attenuation) in the Titan atmosphere, wind noise and turbulence, and saltating sand grain impact. Thus, among the few microphones ever flown to other planetary bodies, MICRO promises to make observations of interest to scientists, engineers, and everyday people alike. Titan’s cryogenic atmosphere, as well as the radiation environment of deep space and of Dragonfly itself, present challenges for the selection of electronics and materials. Following the example of Mars 2020, a commercial-off-the-shelf (COTS) microphone was chosen for its low size, weight and power (SWaP), ruggedness, and suprising compatibility with the hostile Titan environment. An extensive qualification campaign characterized the performance of several COTS microphones and op amps under the stresses of the Dragonfly mission, including radiation dosage and cryogenic temperatures. In addition, mechanical enclosures were designed in order to maximize sound acceptance, while avoiding intrusion of dust and sand. This paper provides an overview of Dragonfly’s MICRO sensor suite, including science impetus, component qualification, design, and test.

Saturn's moon Titan was explored by the Cassini spacecraft from 2004 to 2017. While Cassini revealed a lot about this Earth-like world, its radar observations could only provide limited information about Titan's liquid hydrocarbons seas Kraken, Ligeia and Punga Mare. Here, we show the results of the analysis of the Cassini mission bistatic radar experiments data of Titan's polar seas. The dual-polarized nature of bistatic radar observations allow independent estimates of effective relative dielectric constant and small-scale roughness of sea surface, which were not possible via monostatic radar data. We find statistically significant variations in effective dielectric constant (i.e., liquid composition), consistent with a latitudinal dependence in the methane-ethane mixing-ratio. The results on estuaries suggest lower values than the open seas, compatible with methane-rich rivers entering seas with higher ethane content. We estimate small-scale roughness of a few millimeters from the almost purely coherent scattering from the sea surface, hinting at the presence of capillary waves. This roughness is concentrated near estuaries and inter-basin straits, perhaps indicating active tidal currents.

The surface of Titan is composed of varied geomorphic units indicative of a vivid depositional, erosional and tectonic history. Dominant at Titan's equatorial regions are vast eolian landscapes of dunes, sand sheets, yardangs and wind streaks. These features reveal the action of wind in time and space, which has moved and shaped unconsolidated materials across the surface. Cassini Visual and Infrared Mapping Spectrometer (VIMS) spectra of these materials are most consistent with organics, and particle sizes from Cassini Synthetic Aperture Radar (SAR) vary from dust to cobbles [1]. Most grains appear to be sand-sized, based on the predominance of SAR-dark (smooth at 2 cm) material organized into dune forms at the equator, and models for wind requirements to build dunes on Titan [2]. Dunes cover ~15% of Titan’s surface, or 13 million km2 [3, 4] in the form of linear dunes 1-2 km wide and spaced by 1-4 km [5]. This type and size of dune is dominant in the Arabian and African deserts and is also known as longitudinal [6], referring to the net direction of the transport of sand, which aligns with dune crests [7, 8]. All dunes visible in the Cassini SAR imagery have now been traced down their long axes, revealing regional and global orientations (proxy for wind) and distributions, controlled by obstacles and regional elevations. Over 30,000 dunes have been traced (Fig. 1), and given SAR image coverage, this represents ~40% of all dunes thought to be present based on sand sea locations from the Cassini Imaging Science Subsystem (ISS), meaning we may expect as many as 75,000 dunes to exist on Titan. A total dune length of 1.309 million km has now been calculated from the measured dunes; extrapolated to all of Titan, this length would be 3.273 million km. Using an average dune width of 1 km and corresponding height of 100 m from a 0.1-0.2 dune height:width relationship [9] and isolated measurements [10] we find a total measured dune sand volume of 130,900 km3. If scaled up to all dunes thought to be present, the total volume of sand from dunes alone of 327,250 km3 falls within previous estimates for sand volumes [11, 4, 12]; however, those studies also included sand sheets without detectable dunes. Thus, this new measurement may reveal greater sand volumes from dunes alone than previously thought. This represents a significant material volume that has been moved through wind action, even if from locations close to the (unknown) source. At higher latitudes, several distinct regions of SAR-bright dunes or wind-carved ridges or yardangs are also present (Fig. 2). These can be found in flat plains [13], where they may be inactive dunes, or on the elevated, fluvially carved domes of the midlatitudes, postulated to be volcanic laccoliths [14]. Ash or otherwise derived fine organic grains would be ideally soft yardang materials, comparable to those on Earth, and reveal that winds can also remove substrate on Titan, similar to the action of wind in locations on Mars [15]. Statistical comparisons between possible yardangs support their existence on the domes but are consistent with them being dunes in other locations [16]. The dome yardangs would have resulted from removal of fine-grained materials and loss to the atmosphere as airborne particles and eventually other surfaces – new estimates of the volume of yardang erosion on one small dome, based on yardang heights of ~100 m from shadows, is ~125 km3, and there are a handful of identified other similar yardang regions. Creation of dust from dune sand movement has not yet been estimated (and there are significant uncertainties about material properties) but with yardang processes could yield large volumes that now reside in unknown locations, including interdunes, high latitude plains, lakes and seas. SAR and ISS bright streaks are visible at low to midlatitudes on Titan, similar in orientation to the dunes where they overlap, and found behind obstacles [17, 18]. Their SAR brightness is consistent with a larger particle size, which may be supported by lower density materials, but wind streaks are also often identified with fine particle sizes. This reveals yet another sand and dust location on Titan. Yardangs and wind streaks, along with the ubiquitous equatorial dunes, confirm a general W-E flow of wind, with some N or S deviations that may be reflections of a global undulatory wind pattern at high latitudes. The Dragonfly mission will study dune regions in depth and will reveal particle sizes and compositions, nature of the interdune, level of dune activity and sand (and perhaps dust) movement at the present day, and magnitude and direction of modern winds [19]. These observations will anchor our understanding of eolian processes in the Solar System. [1] Le Gall, A. et al. 2010, Icarus 207, 948-958. [2] Lorenz, R.D. et al. 2006, Science 312, 724-727. [3] Le Gall, A. et al. 2011, Icarus 213, 608-624. [4] Rodriguez, S. et al. 2014, Icarus 230, 168-179. [5] Radebaugh, J. et al. 2008, Icarus 194, 690-703. [6] Courrech du Pont et al. 2024; Earth-Science Reviews, 104772. [7] Lorenz and Radebaugh 2009; Geophysical Research Letters 36. [8] Lucas et al. 2014; Geophysical Research Letters 41, 6093-6100. [9] Lancaster, N. 1995, Geomorphology of Desert Dunes. [10] Neish, C.D. et al. 2010. Icarus 208, 385-394. [11] Arnold, K. 2013, BYU MS Thesis. [12] Lorenz, R.D. et al. 2008, Geophysical Research Letters 35. [13] Lopes, R. et al. 2020. Nature Astronomy 4, 228-233. [14] Schurmeier, L. et al. 2023, Icarus 404, 115664. [15] Kerber, L. et al. 2011. Icarus 216, 212-220. [16] Northrup, D. et al. in progress. [17] Malaska, M.J. et al. 2016. Icarus 270, 183-196. [18] Cohen-Zada, A. et al. 2016. Aeolian Research 20, 108-125. [19] Barnes, J.W. et al. 2021. The Planetary Science Journal 2, 130.Fig. 1. Dunes traced in Shangri-La region of Titan. ISS basemap. Dunes may still be present in large, dark areas, though there is not SAR coverage.Fig. 2. SAR-bright yardangs on an eroded dome. From T64, northern midlatitudes. Arrow shows SAR illumination direction.

Radio links from probes descending into deep planetary atmospheres (Venus, Titan and Outer Planets) show power fluctuations on short timescales (seconds – minutes). These are due to several factors: generally the most significant is the vehicle dynamics which may cause antenna depointing. Propagation factors such as absorption by certain atmospheric gases like ammonia (Jupiter) or sulfuric acid (Venus) can play a role on long timescales. Additional factors, prominent in grazing incidence raypaths, are refractive bending and multipath due to atmospheric inhomogeneities (turbulence, gravity waves) which can cause strong scintillation. The signal power histories from Pioneer Venus, Galileo and Huygens will be reviewed, and expectations for DAVINCI discussed.

Power fluctuations have been noted on radio signals propagating through the Venus atmosphere since the very first descent probe there (Venera 4) and have been observed as a routine feature in radio occultations, where the grazing ray geometry amplifies the effect of refractive scattering structures. Motivated by DAVINCI and other missions currently in development, a physical model of refraction variations in the Venus atmosphere is developed using the VEGA-2 high-resolution temperature profile down to the surface and other data, which suggest several distinct layers of more intense scattering. The resultant modeled radio scintillations are compared with observed scintillations and assessed for the DAVINCI relay link. High-time-resolution radio signal power measurements on the DAVINCI radio link promise to be an interesting probe of the Venus atmosphere

One of the science objectives for Dragonfly, NASA's 4th New Frontiers mission which will explore Titan with a rotorcraft lander, is to measure wind speed and direction on Titan's surface. This will help understand Titan's methane meteorological cycle, and the relationship of Titan's sand dunes to its climate. The Johns Hopkins University Applied Physics Lab (APL) has fabricated and tested a wind sensor patterned closely on the thermal anemometer flown on the Beagle 2 and Schiaparelli Mars missions. An array of 4 such WIND sensors form part of the Dragonfly Geophysics and Meteorology (DraGMet) package, each mounted at the end of one of the rotor arms such that one is always upstream of, and thus unperturbed by, the lander while it is stationary on the surface. This paper describes the design of the WIND sensor, a model for the expected response, the design of a test facility to measure the performance of the wind sensor in its relevant environment, as well as the test data. The challenge for this sensor, and the entire Dragonfly spacecraft, is the environment on the Titan surface, a NitrogenMethane atmosphere at a pressure of 1.5 atmospheres and a temperature of -180 degrees C. The WIND sensor will only be used to measure wind speed and direction on the ground, not during powered flight. APL has built a Titan Pressure Environment Chamber (TPEC) that replicates both the pressure and temperature on Titan, albeit with pure nitrogen (the 5% methane on Titan has only a minimal effect on bulk transport properties such as heat capacity or conductivity). The WIND test enclosure for inside the TPEC creates a microenvironment free of turbulence and houses a motor-driven rotating platform that can accommodate 8 wind sensors for batch testing and can generate relative flow velocities from 0.05 to 5 m/s with a 360-degree directional control for each sensor. Seven generations of prototype sensors have been designed and built, exploring a number of deposition approaches, seed layers, and Rohacell coatings. Each sensor comprises custom platinum (Pt) film resistors that perform a combined heating and temperature sensing function. Three such resistors on a 1cmlong Kapton substrate are mounted on a lightweight Rohacell foam cylinder. The combination of readings from the three films allows retrieval of wind azimuth and speed. The current design, with a 70 nm Pt sputtered film showed the best performance with respect to overall uniformity and resistance variation. Tests have been performed to confirm the film is not significantly affected by erosion. An epoxy coating to mitigate contamination release from the foam has been added. Calibration measurements show that the response to the wind speed, expressed by the Nusselt number, follows the functional dependence derived in a sensor model. The direction dependence is expressed by an angular shear factor, that is the same for all sensors, but, for small Reynolds numbers, depends on the wind speed as well. The TPEC performance tests show that the sensors comfortably meet the measurement requirements outlined for the Dragonfly mission.