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Triton and Pluto are believed to share a common origin, both forming initially in the Kuiper Belt but Triton being later captured by Neptune. Both objects display similar sizes, densities, and atmospheric and surface ice composition, with the presence of volatile ices N2, CH4, and CO. Yet their appearance, including their surface albedo and ice distribution strongly differ. What can explain these different appearances? A first disparity is that Triton is experiencing significant tidal heating due to its orbit around Neptune, with subsequent resurfacing and a relatively flat surface, while Pluto is not tidally activated and displays a pronounced topography. Here we present long-term volatile transport simulations of Pluto and Triton, using the same initial conditions and volatile inventory, but with the known orbit and rotation of each object. The model reproduces, to first order, the observed volatile ice surface distribution on Pluto and Triton. Our results unambiguously demonstrate that obliquity is the main driver of the differences in surface appearance and in climate properties on Pluto and Triton, and give further support to the hypothesis that both objects had a common origin followed by a different dynamical history. [ABSTRACT FROM AUTHOR]

The Perseverance rover is carrying out an original acoustic experiment on Mars: the SuperCam microphone records the spherical acoustic waves generated by laser sparks at distances from 2 m to more than 8 m. These N-shaped acoustic waves scatter from the multiple local heterogeneities of the turbulent atmosphere. Therefore, large and random fluctuations of sound travel time and intensity develop as the waves cross the medium. The variances of the travel times and the scintillation index (normalized variance of the sound intensity) are studied within the mathematical formalism of the propagation of spherical acoustic waves through thermal turbulence to infer statistical properties of the Mars atmospheric temperature fluctuation field. The comparison with the theory is made by simplifying assumptions that do not include wind fluctuations and diffraction effects. Two Earth years (about one Martian year) of observations acquired during the maximum convective period (10:00–14:00 Mars local time) show a good agreement between the dataset and the formalism: the travel time variance diverges from the linear Chernov solution exactly where the density of occurrence of the first caustic reaches its maximum. Moreover, on average, waves travel faster than the mean speed of sound due to a fast path effect, which is also observed on Earth. To account for the distribution of turbulent eddies, several power spectra are tested and the best match to observation is obtained with a generalized von Karman spectrum with a shallower slope than the Kolmogorov cascade, ϕ (k) ∝ (1 + k 2 L 2) − 4 / 3 . It is associated with an outer scale of turbulence, L, of 11 cm at 2 m above the surface and a standard deviation of 6 K over 9 s for the temperature. These near-surface atmospheric properties are consistent with a weak to moderate wave scattering regime around noon with little saturation. Overall, this study presents an innovative and promising methodology to probe the near-surface atmospheric turbulence on Mars. [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]

Acoustics is new on Mars: it allows the characterization of turbulence at smaller scales than previously possible within the lowest part of the Planetary Boundary Layer. Sound speed measurements, by the SuperCam instrument and its microphone onboard the NASA Perseverance rover, allow the retrieval of atmospheric temperatures at 0.77 m above the ground, at 3 Hz, with a ∼10 ms response time that is 20–100 times shorter than for typical thermocouple sensors used on Mars. Here we report on the first measurements of the sound speed‐derived temperature and its fluctuations near the surface. Data highlight large and rapid fluctuations up to ±7 K/s, whose amplitude over such a timescale has never been reported, nor predicted by atmospheric models. These fluctuations follow the daytime pattern of the turbulence and highlight occasional high amplitude events that are likely due to the conjunction of low thermal inertia and strong winds. Plain Language Summary: The atmospheric surface layer of Mars, is prone to various interactions between the surface and the atmosphere, which control most of the climate and the weather of the red planet. There, large temperature gradients generate an intense turbulence during the daytime. Hence, the measurement of the air temperature variations close to the surface is important to understand the spatial and temporal scales of this turbulence. The SuperCam instrument onboard the NASA Perseverance rover enables the retrieval of the near‐surface atmospheric temperatures, and their fluctuations, at an unprecedented short timescale. Sound speed‐derived temperatures, also call sonic temperatures, collected over the Northern spring and summer of Martian Year 36 reveal large and rapid thermal fluctuations up to ±7 K/s, whose amplitude over such a timescale is not reported by any weather station sensors, nor predicted by models that simulate small‐scale eddies. These fluctuations follow the daytime pattern of the turbulence with a maximum amplitude early afternoon. Some occasional high temperature fluctuation events are observed, suggesting a complex effect of ground properties and local meteorological conditions on the turbulence. Overall, acoustics is a new and promising technique that records a unique view of atmospheric temperature variations near the surface of Mars. Key Points: Sound speed derived temperature is used to study the microscale turbulence at an unprecedented short response timeAir temperature experiences fluctuations as high as ±7 K/s, which has never been reported in situ, nor resolved by mesoscale atmospheric modelsSonic temperature fluctuations follow the daytime turbulence pattern and find their origin in complex surface‐atmosphere interactions [ABSTRACT FROM AUTHOR]

Thermal infrared spectra taken by the Emirates Mars Infrared Spectrometer (EMIRS) on‐board the Emirates Mars Mission (EMM) spacecraft are well suited for the retrieval of surface temperatures, the atmospheric temperature profile from the surface to ∼40 km, and the column abundance of dust aerosols, water ice clouds, and water vapor. A constrained linear inversion retrieval routine that includes multiple scattering has been developed and optimized for this purpose. Here, we present a brief overview of the retrieval algorithm and first atmospheric science results from observations taken by EMIRS over the first Earth year of EMM Science Phase operations. These retrievals show extensive water ice clouds, typical for the aphelion season of these observations, and the expected north polar summer maximum and subsequent equatorward transport of water vapor is well documented. An unusually strong and early regional dust storm and its associated thermal response were also observed. Plain Language Summary: Data returned from the Emirates Mars Infrared Spectrometer (EMIRS) have been used to characterize the atmosphere of Mars. These data allow estimates of atmospheric temperature as a function of height, the amount of dust and water ice clouds in the atmosphere, and the abundance of water vapor. In this work we describe the process for estimating these quantities and we give a brief overview of our first results. The results show that Mars was relatively cool, relatively cloudy, but with little dust. This was expected given the season on Mars that was observed. More surprising was the observation of a dust storm that occurred earlier in the Martian year than usual. Key Points: Thermal infrared spectra of Mars taken by the Emirates Mars Infrared Spectrometer have been used to characterize the atmospheric stateThese aphelion season observations show the expected relatively cool atmosphere with prominent water ice clouds and generally little dustThe initiation and evolution of a regional dust storm that occurred unusually early in the season was observed [ABSTRACT FROM AUTHOR]

Abstract: The origin of the detached dust layers observed by the Mars Climate Sounder aboard the Mars Reconnaissance Orbiter is still debated. Spiga et al. (2013, https://doi.org/10.1002/jgre.20046) revealed that deep mesoscale convective “rocket dust storms” are likely to play an important role in forming these dust layers. To investigate how the detached dust layers are generated by this mesoscale phenomenon and subsequently evolve at larger scales, a parameterization of rocket dust storms to represent the mesoscale dust convection is designed and included into the Laboratoire de Météorologie Dynamique (LMD) Martian Global Climate Model (GCM). The new parameterization allows dust particles in the GCM to be transported to higher altitudes than in traditional GCMs. Combined with the horizontal transport by large‐scale winds, the dust particles spread out and form detached dust layers. During the Martian dusty seasons, the LMD GCM with the new parameterization is able to form detached dust layers. The formation, evolution, and decay of the simulated dust layers are largely in agreement with the Mars Climate Sounder observations. This suggests that mesoscale rocket dust storms are among the key factors to explain the observed detached dust layers on Mars. However, the detached dust layers remain absent in the GCM during the clear seasons, even with the new parameterization. This implies that other relevant atmospheric processes, operating when no dust storms are occurring, are needed to explain the Martian detached dust layers. More observations of local dust storms could improve the ad hoc aspects of this parameterization, such as the trigger and timing of dust injection. [ABSTRACT FROM AUTHOR]

Large-Eddy Simulations (LES) for Mars resolve the Planetary Boundary Layer (PBL) turbulent dynamics by using a very fine horizontal resolution of a few tens of meters. LES modeling is becoming a more and more useful tool to prepare the robotic exploration of Mars by providing means to evaluate the intensity of convective plumes and vortices, horizontal wind gustiness, and turbulent fluctuations of temperature in the Martian PBL. In such context, and given the relative paucity of turbulence-related measurements on Mars, an intercomparison of LES models is a fruitful way to evaluate the models' predictions and to indicate possible areas of improvement. Thus, to prepare the landing of the ExoMars Schiaparelli lander (also named ExoMars Demonstrator Module, EDM), scheduled for October 2016, the results of the Laboratoire de Météorologie Dynamique (LMD) and South-West Research Institute (SwRI) LES models have been compared. The objective of this study is to determine the range of uncertainties, and dispersions, of the two numerical models' predictions, for the critical phase of the spacecraft's descent in the Martian daytime turbulent PBL. First, a strategy is defined to ensure similar radiative forcing in both the LMD and SwRI models. Then, LES are performed over a flat terrain with and without large-scale ambient horizontal wind. The LMD and SwRI Martian LES models predict similar temporal evolution of the PBL and organization in the horizontal and vertical wind fields. However, the convective motions in the daytime PBL are more vigorous by a factor 1.5-2 in SwRI results than in LMD results, independently of the presence or not of ambient horizontal wind. This discrepancy is further investigated through sensitivity studies to surface conditions, ambient wind, and airborne dust loading. [ABSTRACT FROM AUTHOR]

The topography of Neptune's large icy moon Triton could reveal important clues to its internal evolution, but has been difficult to determine. New global digital color maps for Triton have been produced as well as topographic data for <40% of the surface using stereogrammetry and photoclinometry. Triton is most likely a captured Kuiper Belt dwarf planet, similar though slightly larger in size and density to Pluto, and a likely ocean moon that exhibited plume activity during Voyager 2′s visit in 1989. No surface features or regional deviations of greater than ±1 km amplitude are found. Volatile ices in the southern terrains may take the form of extended lobate deposits 300–500 km across as well as dispersed bright materials that appear to embay local topography. Limb hazes may correlate with these deposits, indicating possible surface–atmosphere exchange. Triton's topography contrasts with high relief up to 6 km observed by New Horizons on Pluto. Low relief of (cryo)volcanic features on Triton contrasts with high-standing massifs on Pluto, implying different viscosity materials. Solid-state convection occurs on both and at similar horizontal scales but in very different materials. Triton's low relief is consistent with evolution of an ice shell subjected to high heat flow levels and may strengthen the case of an internal ocean on this active body. [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]