Nicholas Gray Heavens

How will climate change affect the composition of the seabed? Ongoing climate change impacts nearly every area of our oceans. While coastal impacts of flooding and erosion are well studied, less attention has been paid to the impact of increased storminess and regional sea level rise on the seafloor, its sediments, and the benthic habitats which rely on it. Making use of a set of 3D hydrodynamic and wave models, and CMIP5 climate projections, we investigate and quantify the drivers of seafloor stresses. Our study maps the potential for grain size mobilisation in current and future projections, highlighting areas where seabed composition is likely to change in future. Sea level rise not only alters absolute water depth but also modifies current stresses by shifting the phase and magnitude of the tides. Rising sea levels also reduce exposure of the seabed to ocean waves. However, increased storm intensity in a warming world will lead to more frequent periodic disturbance of an otherwise increasingly immobile seabed. These predicted changes and their expected impact on the benthic environment are discussed in the context of the increasing anthropogenic activity in the marine environment and the associated challenges in marine spatial management.

To date, Mars’s weather has been monitored mainly from spacecraft in polar or quasi-polar orbits, which sample only a narrow range of local times, or several local times over multiple sols with discontinuous spatial coverage (Fig.1). When observations have been made and/or analyzed at different local times, a high magnitude of diurnal variability often has been found [see e.g. 1 to 5]. The significance of diurnal meteorological variability at Mars argues for orbital observations that span the diurnal cycle. The rapid dynamics of meteorological phenomena such as dust storms (typical timescale of a few hours) and water/CO2 ice clouds (typical timescale of half an hour or less), together with their spatial extension (up to the planetary scale for dust events) and duration/repeatability, argues for continuous and simultaneous observations across the planet (Fig.1). As it happened for the study of meteorology on Earth in the 1970s, now is the right time to introduce monitoring to the observation paradigm for the martian atmosphere, so far almost exclusively focused on mapping. The Emirates Mars Mission (EMM), which entered Mars’s orbit in February 2021, is the first orbiter fully dedicated to the study of its climate. Thanks to its high, eccentric, low inclination orbit, it is also the first satellite that can reasonably observe the evolution of meteorological phenomena over multiple local times simultaneously, thus operating the transition from the mapping to the monitoring paradigm. Although unique so far, EMM alone cannot provide what has been identified as a high priority requirement to improve the spatiotemporal coverage of existing data and to enable future human exploration missions, i.e. global, continuous, and simultaneous monitoring, leading to forecasting of meteorological phenomena [6].Quasi-global monitoring (excluding the polar regions) can be achieved by a constellation of areostationary platforms, i.e. satellites in equatorial, circular orbits in which the orbital period of the satellite matches the rotational period of Mars. The minimum number required for covering all equatorial longitudes is three [7]. The required number to cover all longitudes in a continuous latitude band extending from nearly 80°S to nearly 80°N with some large overlapping in longitude is four (Fig.2). If the areostationary constellation is coupled with at least one satellite in low polar orbit, the continuous (high cadence) and simultaneous (all locations at once) monitoring becomes nearly global [8].Areostationary observations would revolutionize Mars weather forecasting as geostationary satellite imagery did for Earth weather forecasting in the 1970s. The quasi-global, continuous, and simultaneous view that observations from an areostationary network provide would allow forecast initialization from atmospheric states that properly account for teleconnections, large-scale weather and dust events, tides, and other diurnally varying, global-scale phenomena (Fig. 3). Operational monitoring coupled to modelling will enable forecasting, allowing to take preventive actions and minimize risks. It will take several attempts to optimize an operational monitoring and forecasting system, primarily because extreme events such as dust storms attaining the planetary scale occur at irregular times. It is thus essential to send precursor missions aimed at developing the operative infrastructure well in advance of the first human mission. Areostationary platforms do not only offer advantages in meteorology. Satellites in areostationary orbit would spend nearly 75% of their time outside the bow shock of Mars, offering monitoring of the upstream solar wind at an unobstructed vantage point (Fig. 4). The high distance of an areostationary orbit from Mars could also allow for globally mapping the escape of atmospheric species in response to changes in upstream drivers, a task only partially fulfilled by EMM. Last but not the least, areostationary relay satellites could advance telecommunication capabilities for future robotic and human Mars missions far beyond current capabilities [9 to 11]. They are also ideal to support the communication requirements of a future generation of small, low-cost Mars science orbiters and be part of a Global Navigation Satellite System (GNSS), which would greatly improve mission safety and reliability for sustainable, long-term exploration [12]. See [7] for more information on the benefits and applications of satellites in areostationary orbit. Furthermore, the architecture of the constellation, and recent advancements on on-board computational capabilities, would enable significant degrees of autonomy, such as coordination of observations, event-driven operations, and goal-based monitoring.In order to fully shift paradigm from mapping to monitoring, therefore, we have developed a mission concept to send a constellation of at least three satellites in the second half of the current decade, place them in an areostationary orbit, and monitor atmospheric and space weather over the course of at least two Martian years. We name our concept MACAWS, which stands for "Monitoring Areostationary Constellation for Atmosphere and Weather in Space" (Fig. 5). The nature and objectives of this novel mission lend themselves to the use of SmallSats to reduce costs and accept higher risks, while maximizing impact. The scientific and operational achievements of this precursor mission will directly feed into the subsequent planning of larger-scale monitoring constellations.The stated goal of MACAWS is to be a low-cost, precursor, orbital mission to monitor atmospheric and space weather events continuously and simultaneously at most locations on the planet and in the upstream solar wind, in preparation for the human exploration of Mars. The scientific payload, mission architecture, and ConOps are defined accordingly (Fig. 6). The planned outcomes are a better scientific understanding of...

The recent discoveries of telluric exoplanets in the habitable zone of different stars have led to questioning the nature of their atmosphere, which is required to determine their habitability. Atmospheric escape is one of the challenging problems to be solved: simply adapting what is currently observed in the solar system is doomed to fail due to the large variations in the conditions encountered around other stars. A better strategy is to review the different processes that shaped planetary atmospheres and to evaluate their importance depending upon the stellar conditions. This approach allowed us to show that processes like ion-pickup were a more important way to lose atmosphere at Mars in the past. We reviewed the different escape mechanisms and their magnitude in function of the different conditions. This led us to discover discrepancies in the current literature concerning problems such as the Xenon paradox or the importance of a magnetic field in protecting an atmosphere.This shows that one should be very careful before claiming the presence of an atmosphere on planets in the habitable zone of their M-dwarfs: new criteria such as the Alfven surface location with respect to the planet should be taken into account a-priori.Overall, the habitability of a planet should not be claimed only on by its location in the habitable zone but also after careful analysis of the interaction between its atmosphere and its parent star [Gronoff et al. 2020]. Gronoff, G., Arras, P., Baraka, S., Bell, J. M., Cessateur, G., Cohen, O., et al. ( 2020). Atmospheric Escape Processes and Planetary Atmospheric Evolution. Journal of Geophysical Research: Space Physics, 125, e2019JA027639. https://doi.org/10.1029/2019JA027639

The kinetic temperature of the Martian seasonal caps is controlled by the partial pressure of atmospheric CO₂ at the surface. When carbon dioxide condenses, typically near the poles, light non‐condensable species (Ar, N₂, CO, etc.) accumulate in the atmosphere, resulting in a decrease of the CO₂ partial pressure and depressing the local frost point temperature. The buoyant air should mix laterally and vertically within the polar vortices. Observations show that the Martian seasonal caps' kinetic temperatures are ∼0–4 K below the expected CO₂ frost point, depending on latitude and season, indicating atmospheric CO₂ gas depletion at the surface/atmosphere interface. In the North and South, we find relatively similar non‐condensable peak enhancement factors (e.g., EF_NC ∼ 6–8, up to ∼8.7 in the North) at most latitudes, confirming the efficient meridional mixing within the polar vortices, despite steep surface condensation gradients. In the South, this surface enhancement is similar to column‐integrated values derived from Gamma Ray Spectrometer data, indicating efficient vertical mixing. But in the North, the surface depletion is much larger than in the entire column, suggesting poor vertical mixing. Reduced infrared emission of the seasonal caps stemming from CO₂ depletion is not a major energy balance factor. This work illustrates how the atmosphere's composition at the surface can be significantly different from column‐integrated values.

Gravity waves (GW) transfer energy and momentum from the lower to the middle and upper atmospheres of Earth and Mars. Momentum transfer can occur through the wave dissipative process of saturation associated with convective or shear instability. GW saturation both impacts the atmospheric circulation where saturation occurs and also mediates the GW flux above the level of saturation. It was previously demonstrated that convective instabilities are observable in Mars’s middle atmosphere. Here we characterize the seasonal, interannual, and dust event-driven variability in convective instability in Mars’s atmosphere using retrieved temperature profiles from more than 7 Martian yr of observations by the Mars Climate Sounder on board the Mars Reconnaissance Orbiter. The mean probability of convective instability in the middle atmosphere is <1%, except in the upper portions of the winter westerly jets (≈70 km altitude, 60°–75° N/S), near 30°–40° S and ≈60 km altitude on the dayside in southern summer, and in the tropics at 40–50 km altitude around northern fall equinox. Probabilities of convective instability in or near these three regions can increase by an order of magnitude during planetary-scale dust events and some regional-scale dust events. GW-driven drag on both the equatorial easterly jet and winter westerly jet therefore could increase by an order of magnitude during these dust events, as long as changes in GW properties and the local winds do not provide a compensating reduction of the drag.

Martian gravity waves (GW) greatly impact the atmospheric circulation and formation of clouds, but many GW observations of the lower atmosphere are confined to specific orientations and wavelengths, leaving many gaps in the continuum of waves. To overcome the issue, we analyze eight Mars years of data during the season of L _s = 120°–150° from Band 10 (14.9 µm) of the Thermal Emission Imaging System (THEMIS), sensitive to GWs at ∼25 km altitude. All horizontal orientations at wavelengths below ∼40 km are detectable, with the potential to detect north‐south oriented GWs up to ∼1,000 km in length. Most THEMIS observations have brightness temperature variances compatible with GW disturbances. Intense GW activity concentrates poleward of 60°S, with normalized magnitudes up to 10 ⁻⁴ K ² K ⁻² ; activity decreases toward the equator and remains low throughout the northern hemisphere. The interannual intensity of GWs varies by latitude within three regimes of GW length: short (100 km). Gravity wave orientations that are detectable in all directions do not favor a single direction; that is, Martian GWs at 25 km altitude are isotropic. Finally, interannual variability seems to emerge from interactions with dust storms, orography, and planetary waves.

Global climate models typically simulate climate at much larger spatial scales than tropical mountain glaciers and many of the world’s lakes. Yet some of the proxy data that can be used to validate models of past climate on land come from and are related to these geographic features. Validating global climate models using these proxies requires some method of downscaling global climate model output to the resolution of the relevant geographic feature. One possible downscaling technique is to use the global climate model to generate a time-evolving atmospheric state that can be used to force the model’s own land component at much higher resolution than the global model to resolve the relevant geographic features and/or local topography as well as the processes of interest. This dataset contains the output from 50 experiments that use the Community Earth System Model version 2 (CESM2) and its land component, the Community Land Model (version 5) to downscale climate simulations of pre-industrial, Last Glacial Maximum, and an extreme glacial climate with gross similarities to hypothetical late Paleozoic conditions (but within a Last Glacial Maximum paleogeography) to better resolve tropical mountain glaciers in various parts of the world and in one case, a lake. These experiments largely interpolate the land properties assumed by the relevant global climate model simulation to a 100 point per degree grid in a domain that is 1 in longitude and 2 in latitude. Global, high-resolution topography, and sometimes lake distribution datasets are then used to provide information about topography and other properties on the 100 ppd grid. The experiments are then run for 30 or 60 years. The dataset also contains global climate model simulation output of the model experiments used to generate the atmospheric forcing, simple analyses of tropical mountain glacier stability and extent in the experiments, and the code necessary to reproduce these experiments or apply them to other spatial domains.

Connecting upper-atmospheric gravity waves (GW) to their lower- and middle-atmospheric (0–30 and 30–100 km altitude) origins can improve understanding of the evolution of Mars’s atmosphere as well as its present thermal structure and general circulation. A recent study using observations from the Mars Climate Sounder (MCS) on board the Mars Reconnaissance Orbiter (MRO) characterized the climatology of lower-atmospheric GW with 10–100 km horizontal wavelengths, but GW observed in the upper atmosphere have horizontal wavelengths of up to 500 km, motivating more careful attention to the horizontal wavelength spectrum of lower-atmospheric GW. A previous study of observations by the Thermal Emission Spectrometer (TES) on Mars Global Surveyor (MGS) reported substantial interannual variability in the horizontal wavelength spectrum of wave activity defined broadly, including GW. Here, we derive the horizontal wavelength spectrum of wave activity from the brightness temperature variance spectrum of MGS–TES observations resampled to the MRO–MCS spectral channels during L _s = 120°–150°, Mars Years 24 and 25. Lower-atmospheric wave activity is strongest at wavelengths 1000 km, which appears to be a mixture of tides and planetary waves. We find that interannual variability in GW activity previously identified using MGS–TES data largely arises from a change in the instrumental noise characteristics of MGS–TES during the first quarter of MY 25.

Gravity waves are one way Mars’s lower atmospheric weather can affect the circulation and even composition of Mars’s middle and upper atmosphere. A recent study showed how on-planet observations near the center of the 15 μm CO₂ band by the A3 channel (635–665 cm⁻¹) of the Mars Climate Sounder on board the Mars Reconnaissance Orbiter could sense horizontally short, vertically broad gravity waves at ≈25 km above the surface by looking at small-scale radiance variability in temperature-sensitive channels. This approach is extended here to two additional channels closer to the wings of the 15 μm CO₂ band, A1 (595–615 cm⁻¹) and A2 (615–645 cm⁻¹), to sense gravity waves throughout the lower atmosphere. Using information from all three channels demonstrates that gravity-wave activity in Mars’s lowermost atmosphere is dominated by orographic sources, particularly over the extremely rough terrain of Valles Marineris. Much of this orographic population is either trapped or filtered in the lowest two scale heights, such that variations in filtering and nonorographic sources shape the gravity-wave population observed at 25 km above the surface. During global dust storms, however, gravity-wave activity in the first scale height decreases by approximately a factor of 2, yet trapping/filtering of what activity remains in the tropics substantially weakens. Exceptionally high radiance variability at night in the tropics during the less dusty part of the year is the result of observing mesospheric clouds rather than gravity waves.