Abstracts 2022
Session One: Terrestrial Worlds
Theory, models, and methods: Translating Earth science to planetary atmospheres
William Seviour, Department of Mathematics and Statistics, University of Exeter
Spacecraft observations during the past two decades have given us the first truly global measurements of atmospheres beyond our own. In this talk, I will draw parallels between our knowledge of Earth’s atmosphere at the dawn of the satellite age and our knowledge of some solar system planetary atmospheres today. I will focus on the large-scale circulation of terrestrial planetary bodies, particularly Mars and Titan, where these parallels relate to the theoretical approaches to understanding atmospheric circulations, the numerical modelling used, and the methods to process and interpret data.
Theoretical parallels include the calculation of global potential vorticity (PV) fields for Mars and Titan, echoing the low-resolution ‘knobbly-glass’ calculations for Earth’s stratosphere in the early 1980s. PV is a key dynamical variable, and these calculations have recently enabled deeper insight into the dynamics of planetary polar vortices and the processes driving their structures. Modelling parallels come not just in the development of ever-more complex general circulation models, including aerosols, clouds, and hydrological cycles, but also in the use of idealised modelling approaches to probe the roles of different physical processes. Such idealised modelling includes 2D shallow water and 3D dry primitive equation simulations, both of which have a rich history in understanding Earth’s atmospheric circulation. Methodological parallels include the recent development of reanalysis datasets for Mars. These reanalyses are powerful tools, first developed for Earth’s atmosphere in the 1990s as a method to combine a wealth of observational data to provide global state estimates, and are already leading to valuable new insights.
Investigating the 2007 global dust storm at Mars with Mars Express
Catherine Regan
Global dust storms at Mars cover the entire planet causing increases in temperature and ion escape as dust is lifted up to 80 km in altitude. The two most recent storms occurred in 2007 (Mars Year (MY) 28) and 2018 (MY34), and have been observed by spacecrafts such as Mars Express (MEx). MEx has been operating at Mars since 2004, and has produced a long time-base of plasma measurements from as low as 250 km. Using MEx, we investigate whether the 2007 dust storm has influenced the magnetosphere of Mars by looking at the position of the bow shock and induced magnetospheric boundary, compared to the expected position provided by 3D magnetohydrodynamical models. To identify boundary positions, we use data from the ASPERA-3 instrument (Analyser of Space Plasma and EneRgetic Atoms) onboard MEx, which contains an electron spectrometer (ELS), ion mass analyser (IMA), neutral particle imager (NPI) and neutral particle detector (NPD). For this study, we use data from ELS and IMA. We consider a number of influences on the boundary position, including the solar wind conditions and the crustal fields. Our study period includes time before, during, and after the MY28 global storm, and we expected the bow shock and induced magnetospheric boundary to increase in altitude due to the storm. Out results show that the system is more complex, and multiple influences need to be distinguished to leave any change due to the dust storm itself.
JCMT-Venus - monitoring the atmosphere of Venus at mm wavelengths
David L Clements
The JCMT-Venus project is a long term JCMT programme aimed at monitoring several chemical constituents of Venus’ atmosphere at mm wavelengths to determine how their abundance varies on timescales of hours to years. The principle targets of these observations are HDO, SO2 and PH3. The latter, PH3, phosphine, is of particular interest given its recent discovery in the atmosphere of Venus since it cannot be produced in the abundances seen by conventional chemical processes. By monitoring how PH3 abundance varies in relation to the abundances of HDO and SO2 we will be able to uncover clues as to the origin of this unexpected molecule. The passband of the Ū’ū receiver used for these observations will also allow several other species, eg. HCO+ and H2SO4, to be detected and monitored. The first observing campaign for this project has already been completed, with to more campaigns due to take place over the next year.
Evidence for a Global Atmospheric Electric Circuit on Venus
Blair McGinness
The electrical environment of Venus has been investigated through extensive considerations of the presence of lightning on the atmosphere [1]. Although a very important process, the presence or absence of lightning does not completely describe the Venusian electrical environment. Little consideration has been made for other aspects of the electrical environment, such as the possible presence of a global atmospheric electric circuit, as is present on Earth. New arguments for and against a global circuit in Venus’ atmosphere have been developed through re-analysis of data from the Venera 13 & 14 landers.
On Earth, the global atmospheric electric circuit connects regions of disturbed weather to regions of fair weather by continuously distributing electric charge across the conducting ionosphere and surface. Disturbed weather regions create a potential difference between the ionosphere and surface by transferring electric charge between them. For observers on Earth’s surface, this charge transfer is most dramatically illustrated by cloud-ground lightning strikes, however these processes are only one method in which this charge transfer takes place [2]. The global atmospheric electric circuit is then completed by a “fair weather conduction current” which flows between the surface and ionosphere in fair-weather regions. The potential difference sustained between the ionosphere and the surface leads to a vertical electric field being present in the atmosphere.
The Venera 13 & 14 landers carried a wealth of instrumentation during their descent through the Venusian atmosphere. Among these instruments were point discharge sensors, which recorded electrical discharges between the spacecraft and the atmosphere [3]. The currents recorded by these sensors were difficult to explain by simple models of Venus’ environment, so it has previously been proposed that low atmosphere haze layers could have caused them [4]. We have attempted to investigate whether this is a plausible explanation.
To address this question, a model describing electrical interactions of Venus’ atmosphere was produced. This finds, analytically, the concentration of ions in the atmosphere by considering the steady state solution to ion-aerosol balance equations. This electrical model further determined the conductivity of the atmosphere as a function of height, as well as the integrated columnar resistance. These quantities were used to determine the charge accumulated on a hypothetical spacecraft descending through the atmosphere, for cases where an electric field was present or absent.
This electrical model was then used to compare the potential difference between the spacecraft and the atmosphere with the electrical discharges recorded by the Venera landers. Several haze layers were included into the electrical model to see if the Venera results could be reproduced. Preliminary investigations show that similar results to the Venera data can be produced by the electrical model when a background “global circuit” electric field present, but not when it is absent. In addition, if the Venera results were in fact caused by a low atmosphere haze layer, then it is highly likely that a global electric circuit would also need to be present.
These findings are not definitive, but they do suggest, under the best assumptions from what is known, what is more or less likely in the Venusian atmosphere. To build more confidence in the original sounding data, the operation of the point discharge sensor is being investigated in more detail, allowing the results from the model to be more quantitatively compared against the Venera data.
References: [1] R.D. Lorenz (2018). Progress in Earth and Planetary Science, 5. [2] J.A. Chalmers (1968). Weather, 23. 442. [3] L. Ksanfomality et al. (1982). Soviet Astronomy Letters, 8. 230–232. [4] R.D. Lorenz (2018). Icarus, 307. 146-149.
Planetary Waves Traveling between the Mars Science Laboratory and Mars 2020 Rovers
Michael Battalio
Mars Science Laboratory (Curiosity) and Mars 2020 (Perseverance) combine to form a surface meteorological network. They uniquely determine wave characteristics with a period of 1.5–30 sols (Mars days) in the temperature, pressure, and relative humidity; Perseverance also detects waves in the winds. By removing the seasonal trend (>30 sols) to separate transients from quasi-stationary periods, then filtering at <1.5 sols to eliminate the tides, planetary waves emerge during northern spring (Ls=19–155°), when baroclinic waves are usually weak. Wave periods of ~2, 3, and 4.5 abound, with pressure, temperature, relative humidity, and wind amplitudes peaking at 2 Pa, 2 K, 2%, 1 m/s, respectively. Simultaneous detection of waves by both rovers across multiple variables indicates planetary-scale waves. Many wave signals correlate or anti-correlate between Curiosity and Perseverance, suggesting waves originate in both the northern and southern hemispheres. Further, despite its more westward longitude, waves at Perseverance do not always lead waves at Curiosity, implicating multiple wave types, specifically baroclinic and barotropic processes. The amplitudes and driving instabilities of the observed waves support the diagnosis of wave structure and energetics within the Ensemble Mars Atmosphere Reanalysis System (EMARS). However, wave amplitudes do not always match between the reanalysis and observations, suggesting that assimilation of observations might improve the representation of the EMARS dataset.
Photochemical fractionation of C isotopes in the atmosphere of Mars
Juan Alday
Isotopic ratios in planetary atmospheres provide important constraints on the planetary evolution. On Mars, a relative enrichment of the heavy isotopes in different species with respect to Earth is thought to be in part due to the result of atmospheric escape, a process which is believed to have played a critical role in driving climate evolution over the last four billion years. However, isotopic ratios not only provide constraints from the long-term perspective, but also are shaped by present-day atmospheric processes. Here, we investigate the fractionation of the C isotopes in the atmosphere of Mars using a combination of measurements from the ExoMars Trace Gas Orbiter, together with the predictions from a 1D photochemical model. Our results show that the photochemical cycles operating today in the Martian atmosphere can give rise to a measurable depletion of the 13C/12C ratio in CO with respect to CO2.
Magnetic and Electric Fields of Martian Dust Storms – an Experimental Approach
David Reid
Despite no direct observations of lightning on Mars, it is expected to occur. The planet is known to have large dust storms -which are believed to become charged with electric fields in the region of 100 kV/m (as observed in terrestrial dust storms), due to a phenomenon known as triboelectrification. On Mars, the same process is expected and as this magnitude of field is larger than the breakdown field strength of Mars, discharges can be expected although they may occur differently on Mars than they do on Earth. Magnetic fields are also expected in dust storms both on Earth and on Mars – though there are currently few measurements of this property
Understanding of electric and magnetic fields of this prevalent feature of the Martian landscape is vital to understanding and developing missions of Mars. When dust becomes electrified it strongly adheres to surfaces – an issue for power generation and scientific instrumentation. Electrification on Mars has also been shown to cause phase change and amorphization in sulphur and chlorine salts, altering the Martian surface materials. There is also evidence to suggest that the electrical activity of dust storms might act as a sink for methane and understanding of the electric fields is important to the understanding of the sources and sinks of this potential biomarker on Mars. Understanding of magnetic fields of Martian dust storms is also important, with future Mars missions set to carry magnetometers.
Two hypotheses were postulated. Firstly, the vertical separation of charge is responsible for the electric field, and, secondly, that the spiralling motion of the charged particles is responsible for the magnetic field. An experimental apparatus was designed to isolate the vertical and horizontal components of the motion in a dust storm. Using an electric field mill (CS110) and search coil magnetometer (LEMI 133, the engineering model from the postponed ExoMars22 mission), the desired fields were measured. Preliminary results from the commissioning of the experimental rig are presented.
A climatology of gravity wave activity in Mars’s middle atmosphere from Mars Climate Sounder limb observations
Nicholas G. Heavens
Gravity waves are one means to transfer energy and momentum between widely separated regions of a planetary atmosphere. Sources as wide-ranging as the interactions of the wind with topography, convection, and possibly baroclinic instability structures excite these waves, making gravity waves just as much clues to the tumult of the atmosphere close to the surface as they are perturbers of the structure and dynamics of the middle and upper atmosphere. At Mars, records are gradually building up of gravity wave activity in both the lower and upper atmosphere, including spatial, seasonal, and interannual variability. Changes in gravity wave activity observed during Mars’s planetary-scale and regional dust events have been simultaneously striking and puzzling. Gravity wave activity in the middle atmosphere, however, has been less well characterised. In this presentation, I will show how series of long continuous limb scans by the Mars Climate Sounder on board Mars Reconnaissance Orbiter can be used to quantify the activity of gravity waves with vertical wavelengths close to 5 km and horizontal wavelengths of 100–300 km in the middle atmosphere. I then will focus on testing how gravity wave activity in this portion of the spectrum changed during the planetary-scale dust event in 2007.
Investigating the martian water cycle through data assimilation
James Holmes
Understanding of the martian water cycle, in particular the vertical distribution, holds the key to outstanding questions related to Mars such as how much water has been lost from the atmosphere over time and how does this process vary on monthly and yearly timescales. To better understand how water vapour is transported throughout the atmosphere of Mars requires a global perspective of the combined vertical and horizontal distribution of water. Recent vertical profiles of water vapour from the ExoMars Trace Gas Orbiter mission provide for the first-time systematic mapping of the 4-D structure of water vapour but also suffer from large spatiotemporal gaps. By combining a global circulation model of the martian atmosphere with satellite observations of water, temperature and dust from multiple spacecraft we can investigate the water vapour cycle and the physical processes that result in the observed vertical distribution of water vapour. This statistically optimal unified dataset can be used to investigate multiple features such as the effect of a regional dust storm on water transport and water loss, global transport across multiple timescales and the saturation state of the atmosphere (that is indirectly impacted by water/temperature and dust assimilation). Results from such investigations utilising the Mars Planetary Climate Model (UK spectral) coupled to the analysis correction assimilation scheme will be discussed.
A climatology of super-rotation in 12 years of martian reanalysis data
Kylash Rajendran
A planetary atmosphere is said to be super-rotating if the total axial angular momentum of the atmosphere is greater than the angular momentum of its solid-body component; this often manifests as a westerly jet at the equator, and therefore can substantially impact the distribution of aerosols and chemical species in the tropics. In this work we present a multi-year study of super-rotation in the martian atmosphere using the OpenMARS [1] reanalysis dataset, in order to examine the relationship between dust and tropical winds on Mars. We found that martian super-rotation follows a clear seasonal cycle, with maxima occurring at equinoxes and minima at the solstices. The seasonal structure was found to be directly related to variations in the strength of the extratropical jets. Inter-annual variability was dominated by variations in the tropical circulation, with the largest amount of variability found during the dusty season. Dust loading in the atmosphere was found to have the most significant impact on the tropical circulation close to equinox and had surprisingly little impact at solstice. This effect was clearly seen by comparing the impacts of equinoctial and solstitial global dust storms (GDS) on super-rotation. Whereas the equinoctial GDS caused atmospheric super-rotation to increase by a factor of two [2], during the solstitial GDS there was barely any change in super-rotation. Our results suggest that the background atmospheric circulation has an important role in controlling the strength of atmospheric super-rotation, and therefore constrains the potential evolution mechanisms of global dust storms.
[1] Holmes, J. A. et al (2020), Planet. Space Sci., 88, 104962, https://doi.org/10.1016/j.pss.2020.104962 [2] Rajendran, K et al (2021), Geophys. Res. Lett., 48, e2021GL094634, https://doi.org/10.1029/2021GL094634
Mars’ northern polar vortex: interannual similarities, interannual differences
P. M. Streeter [1], S. R. Lewis [1], M. R. Patel [1,2], J. A. Holmes [1], K. Rajendran [1]; [1] School of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, U.K., [2] Space Science and Technology Department, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell Campus, Didcot, Oxfordshire OX11 0QX, U.K.
Like many planets, Mars’ winter atmosphere is characterised by the presence of polar vortices: regions of low temperatures around the pole, surrounded by powerful jets [e.g. 1,2]. These vortices are crucial components of the planet’s atmospheric circulation, with significant impacts on the transport of dust, water ice, and chemical species, and are themselves influenced by factors such as atmospheric dust loading [e.g. 3,4]. The cold temperatures in the vortices also enable the condensation of atmospheric CO2, which dramatically alters the global atmospheric mass budget on seasonal timescales every martian year [5], while powerful westerly jets form effective barriers to intra-polar transport of atmospheric tracers [6] and control the shape of the polar hood cloud belt via interactions with zonal topography [7]. Additionally, understanding the behaviour of the vortices may help provide insights into the historical climate of Mars, which is recorded in ice and dust layers in the permanent polar caps [8].
We present results from an eight martian year climatology of the north polar vortex, from analysis of the OpenMARS reanalysis dataset [9]: an assimilation [10] of Mars Climate Sounder (MCS) remote sensing observations of dust and temperature [11,12] into a Mars Global Climate Model (MGCM) [13]. Our results show that the large-scale seasonal behaviour and morphology of the vortex displays high interannual repeatability, with the important exception of large dust storm effects. By considering a multi-annual period including two global dust storms and multiple regional dust storms, we investigate the complex effects of both dust storm intensity and dust storm seasonal timing in determining polar vortex changes, as suggested by previous work [14]. We find that the seasonal timing of large-scale dust events does indeed play a crucial role in controlling impacts of such events on the north polar vortex. The importance of seasonal timing is linked to the background atmospheric circulation, such as the seasonally-varying structure of the mean meridional circulation. This has important implications for the relative effects on the vortex of A (earlier-season) and C (later-season) type [15] regional dust storms, as well as solstitial and equinoctial global dust storms.
References: [1] Waugh, D. W. et al (2016) J. Geophys. Res. Planets, 121, 1770-1785. [2] Mitchell, D. M. et al (2015) Q.J.R. Meteorol. Soc., 141, 550-562. [3] Guzewich, S. D. et al (2016) Icarus, 278, 100-118. [4] Ball, E. R. et al (2021) Planet Sci. J., 2, 203. [5] Haberle, R. M. (ed.) (2007), “The Atmosphere and Climate of Mars”. [6] Holmes, J. A. et al (2017) Icarus, 282, 104-117. [7] Haberle, R. M. et al (2019) Icarus. [8] Seu, R. et al (2018) J. Geophys. Res. Planets. [9] Holmes, J. A. et al (2019) “OpenMARS database”. [10] Lewis S. R. et al (2007) Icarus, 192(2), 327-347. [11] McCleese D. J. et al (2010) J. Geophys. Res., 115(E12016). [12] Kleinböhl A. et al (2017) J. Quant. Spectrosc. Radiat. Transfer, 187, 511-522. [13] Forget F. et al (1999) JGR, 104, 24155-24175. [14] Streeter, P. M. et al (2021) J. Geophys. Res. Planets. [15] Kass, D. M. et al (2016) Geophys. Res. Lett., 43.
Modern-day Mars climate in the Met Office Unified Model: dry simulations
Denis Sergeev
We present the first results from the Met Office Unified Model (UM), a world-leading climate and weather model, now adapted to simulate a dry Martian climate. We focus on the effect of dust on the large-scale atmospheric circulation and temperature regime. This is done by running two simulations, one with radiatively active dust, and one with radiatively inactive dust. Our simulations demonstrate how the radiative effects of dust act to change the temperature distribution, affecting the global wind structure, especially during the dusty season. We also validate our model by comparing it to another Mars GCM, the Laboratoire de Météorologie Dynamique Mars Planetary Climate Model (PCM). We find good agreement in the seasonal wind and temperature profiles, but some discrepancies in the predicted dust concentration and overall conditions in high latitudes. This study paves the way for the UM to be used for the Martian atmosphere and suggests that the adaptation of an existing Earth GCM can be beneficial for the Mars modelling community.
Session Two: Atmosphere-Magnetosphere Interconnections
From the depths of the atmosphere to the dusty vacuum of space
Luke Moore
Planetary upper atmospheres mark the transition from a dense atmosphere below to the rarified environment of space above. As such, they mediate the exchange of particles, momentum, and energy between these two distinct regions. In this talk, I will review the various process that couple planetary atmospheres to the space environment, and I will emphasize the signatures of that coupling that are present in the upper atmosphere. From above, solar EUV photons and energetic particle precipitation – leading to auroral emissions – are the most prominent transfer of energy. From below, upward propagating gravity and acoustic waves disrupt the steady-state patterns present in the tenuous upper atmosphere. Both downward and upward coupling lead to significant but relatively short-lived modifications of the local plasma conditions. Remote measurements of giant planet ionospheres therefore serve as excellent probes of this dynamic atmospheric region and the processes that drive it.
An investigation of Jupiter’s Ionospheric Outflow under varying auroral conditions
H. S. Joyce (1), L. C. Ray (1), C. S. Arridge (1), N. A. Achilleos (2); [1] Lancaster University, Lancaster, UK; [2] University College London, London, UK.
Ionospheric outflow is the process in which ionospheric ions are accelerated out of the ionosphere towards the magnetosphere due a pressure gradient between the two regions. At Earth, this process is a significant source of plasma for the magnetosphere during quiet periods. At Jupiter, however, the importance of ionospheric outflow as a source of light ions for the magnetosphere is not yet well understood as the dominant source of plasma is from moons e.g, Io, Europa. Quantifying the rate of ionospheric outflow under varying auroral conditions is an essential first step in understanding how this plasma affects jovian system dynamics.
We use the recently developed IonoSpheric Outflow in Rapidly Rotating Systems (ISORRS) model [Martin et al. 2020a;b] to show that the ionospheric outflow rate is non-uniform across Jupiter. We will apply atmospheric temperature and density profiles from the Jovian Ionosphere Model (JIM) [Achilleos et al. 1998] to explore regions of the atmosphere under different auroral conditions. Our results show that the outflow rate is affected by multiple different parameters such as the auroral width, auroral current densities, and atmospheric temperature.
The Role of Vortex Shielding on Polar Crystal Formation & Vortex Dynamics on Jupiter
Aaron Carruthers
The Juno mission in 2016 revealed that Jupiter’s polar regions contain a set of vortices cohabiting in tightly- packed crystal formations. These crystals were noted for their remarkable stability, even withstanding the intrusion of a stray cyclone drifting into the arrangement. Wind and infrared measurements of these vortices give estimates of their radial extent and velocity profiles, indicating these vortices are surrounded by an annulus of opposing potential vorticity (pv), commonly referred to as a shield.
However, the underlying mechanisms that lead to the development and maintenance of vortex shielding on planetary vortices are generally poorly understood. For example, the sensitivities of the shielding process to planetary parameters, such as deformation radius, are largely unexplored.
Recent work has shown that, in a shallow water framework, these shields are pertinent to the crystal stability. Particularly, recent modelling efforts have placed strict bounds for this shielding in terms of magnitude. Although much work has been devoted to this topic, there are still significant questions remaining and large gaps in our understanding of these polar vortex crystals.
Here we present a preliminary exploration of the parameter space, using a quasi-geostrophic beta plane model to simulate the drift of Gaussian pv pulses in Jupiter-like conditions. These initial results indicate that vortex shielding may have a strong dependence on the deformation radius and the background pv gradient, suggesting a strong dependence on latitude. These preliminary results will form the basis of our work modelling Jovian polar crystal formation and vortex shield development in more detailed atmospheric settings.
Solving the Mystery of Saturn’s PPOs Using Keck-NIRSPEC
Nahid Chowdhury
The earliest Voyager data on Saturn’s radio emissions from the 1980s were used to deduce a proxy for the rotation rate of the ringed planet. However, the advent of the Cassini mission at the turn of this century revealed that this rotation rate appeared to have lengthened by nearly 6 minutes since Voyager. As it was unlikely that the physical rotation rate of the planet would have changed in the intervening time period, it was instead hypothesised that something interior to the planet had altered to cause this shift.
Several theories have been touted in an attempt to explain the mysterious periodicities and time variabilities witnessed in planetary parameters throughout the Saturnian environment. These theories are broadly grouped into two different schools of thought: 1) a driving mechanism based in the planet’s magnetosphere, exterior to the planet itself, is responsible for the observed behaviour; or, 2) a driving mechanism based within the planet, perhaps in the upper atmosphere, is instead responsible.
We investigated the notion that an atmospheric “twin-vortex” might be the driver of the time variabilities witnessed at Saturn using Keck-NIRSPEC observations from June, July and August 2017. These data allowed us to map the ion flows in the planet’s atmosphere after initially grouping the spectra into bins of planetary magnetic phase. Doing so provided the first direct detection of Saturn’s upper atmospheric “twin-vortex mechanism and solved a decades-long mystery in the process. This poster summarises the careful observations and subsequent analysis that went into producing this ground-breaking seminal result.
Ionospheres through the Solar System: from comets to moons of gas giants
Arnaud Beth
Previous (Galileo), recent (Rosetta, Juno) and upcoming (Comet Interceptor, JUICE) missions aim at exploring the close space environment of planetary bodies such as moons (e.g. Ganymede) and comets (e.g. 67P) showed that there are still rooms and gaps in our understanding of the complex interaction between the neutral environment surrounding Solar System bodies and any external sources such as the Sun or their hosting planets.
While ubiquitous in nature, ionospheres – identified as the partially-ionised layer embedded into the atmosphere – that surround comets, moons, and planets behave very differently in terms of dynamics, chemistry, and energetics. Although the primary mechanism at the origin of the formation of an ionosphere remains the same (i.e. ionisation of the neutral atmosphere), their characteristics may vary drastically between bodies based on: the altitude profile of the neutral density and the source of ionisation. Regarding the first difference, unlike large bodies with atmospheres retained by gravity, comets have a continuous expanding atmosphere escaping to space. This difference strongly influences the way that photons can pass through the coma before ionising neutrals: the maximum of absorption does not occur at the same optical depth for comets and for planets/moons whose atmosphere is under hydrostatic equilibrium. The second main difference is the source of ionisation. Unlike magnetised bodies, such as most planets and moons, comets are not protected from energetic external plasma flow (either the solar wind in the case of planets and comets, or the corotating plasma present within large magnetospheres, like at Jupiter, for the moons) such that the latter can access the inner part of the atmosphere, be energised, and hence being responsible for the ionisation and excitation of neutrals.
The non-ambiguous identification of these drivers and how ionospheres are driven require multi-instrument analysis of neutral gas, particle, plasma and/or optical dataset (e.g. by combining local neutral density observations, electron energy distribution, electron number density, Far UltraViolet (FUV) remote sensing observations), linked together with physics-based models. This allows to build a self-consistent picture of the interaction of the atmospheric layer with the space environment of the body. We will show examples of how such an approach has been successfully applied in the case of Rosetta at 67P and Galileo at Ganymede and are essential in the preparation of future missions.
Ionospheric composition of comet 67P near perihelion with multi-instrument Rosetta datasets
Zoe Lewis
The European Space Agency Rosetta mission escorted comet 67P/Churyumov-Gerasimenko for two years, during which it acquired an extensive dataset, revealing unprecedented detail about the neutral and plasma environment of the coma. The measurements were made over a large range of heliocentric distances, and therefore of outgassing activity, as Rosetta witnessed 67P evolve from a low-activity icy body at 3.8 AU to a dynamic object with large-scale plasma structures and rich ion and neutral chemistry near perihelion at 1.2 AU. One such plasma structure is the diamagnetic cavity, formed when mass loading by cometary ions prevents the solar wind (and therefore the interplanetary magnetic field) from penetrating the inner coma, leaving a magnetic field free region around the nucleus.
In this study, we focus on the changing role of chemistry in the coma during the escort phase, particularly on trends in the detection of high proton affinity species near perihelion and within the diamagnetic cavity. NH4+ is produced through the protonation of NH3 which has the highest proton affinity of the neutral species and is therefore the terminal ion. We use data from the ROSINA (Rosetta Orbital Spectrometer for Ion-Neutral Analysis)/DFMS (Double Focussing Mass Spectrometer) instrument, which was the first instrument with sufficient mass resolution to separate H2O+ and NH4+, enabling the unambiguous detection of NH4+ in a cometary environment for the first time. We analyse this ion mass spectrometer data alongside a range of plasma properties from the RPC (Rosetta Plasma Consortium) suite of instruments and compared to ionospheric model outputs to further evaluate the relative significance of ion-neutral chemistry and transport and how this impacts the ionospheric composition within different interaction regions.
Thanks to this multi-instrument analysis, we show that increased comet outgassing at perihelion allows more complex ion-neutral chemistry to occur, resulting in more detections of protonated High Proton Affinity species by ROSINA/DFMS at this time. We also observe a link between presence of the diamagnetic cavity and higher NH4+ counts, that is shown not to be driven solely by variation in spacecraft potential. This suggests transport may be a more significant loss process outside the diamagnetic cavity, and that plasma dynamics are an important factor affecting the ion composition of the coma. It also highlights the importance of multi-instrument analysis to put individual ion measurements into context.
‘Pro-Am’ synergy in understanding Jupiter’s chaotic cyclonic regions
John Rogers
Collaboration between ground-based amateur imagers and the NASA JunoCam team is contributing to new insights into Jupiter’s atmosphere, exemplified by cyclonic ‘folded filamentary regions’ (FFRs) in the northern hemisphere. Ground-based tracking of these and associated ovals reveals details of the zonal flows and mutual interactions. JunoCam imaging reveals details of the cloud structures, including multiple cloud or haze layers, lobes apparently expanding over neighbouring features, hazes with relatively orange or green colours in different locations, and eruptive plumes consisting of dense packs of ‘pop-up clouds’. The latter are very likely to be thunderstorms according to results from previous spacecraft and from Juno. The JunoCam images will also open the way for measurements of relative cloud heights, from parallax and from shadowing, and for joint studies with other Juno and ground-based instruments probing below the main cloud layers in microwave and infrared wavebands.
External water flux into Uranus and Neptune’s atmospheres
Nicholas Teanby
Observations of the 557GHz emission line using Herschel Space Telescope’s HIFI instrument are used to constrain water flux into Uranus and Neptune’s stratospheres. Externally sourced water is mostly expected to be from interplanetary dust particles (IDPs) generated within the Kuiper Belt or debris from various comet families. The Herschel/HIFI observations show that Neptune has around four times as much stratospheric water as Uranus. However, once the warmer stratosphere of Neptune is taken into account, these results imply that external water flux into each planet’s atmosphere is the same to within errors; around 10^5 molecules/cm^2/s with a ~20% uncertainty. This is somewhat unexpected as Neptune is closer to the Kuiper belt, so current IDP dynamical models predict it to have a much greater IDP/water flux. In fact, the measured flux at Neptune is about an order of magnitude less than current model predictions. Interestingly, a similar flux for each planet is also supported by measurements for micron-sized IDPs measured by New Horizons’ Student Dust Counter instrument, which show roughly constant flux in the 20–30 a.u. range. The HIFI observations provide the best constraints on stratospheric water to-date and show that IDP flux models of the outer solar system need to be revisited.
Teanby et al. (2022) Uranus’s and Neptune’s Stratospheric Water Abundance and Vertical Profile from Herschel-HIFI, Plan. Sci. J., 3:96, https://doi.org/10.3847/PSJ/ac650f
Investigating the thermal contrast between Jupiter’s belts, zones, and polar vortices with the VLT/VISIR
Deborah Bardet
Ground- and space-based remote sensing, from Voyager, to Galileo, Cassini and Juno, has revealed the existence of circulation cells (Duer et al., 2021) in the troposphere of Jupiter. These circulation cells, which may be similar to terrestrial Ferrel cells, show properties that vary significantly as a function of depth, showing circulations of opposing directions above and below the expected level of the water condensation cloud near 4-6 bar (Fletcher et al., 2021). Moreover, the location of each vertical branch of the Ferrel-like cells are correlated to the Jupiter’s temperature belt/zone contrast, suggesting a dynamical and thermal link between winds, temperatures, aerosols, and composition.
To provide infrared support for Juno spacecraft observations, we have been observing Jupiter with the VISIR mid-infrared instrument on the Very Large Telescope (VLT) since 2016. We analyse images at multiple wavelengths between 5 and 20 µm to study the thermal, chemical and aerosol structure of Jupiter’s belts, zones, and polar domains. In particular, an observing run in May 2018 (conciding with Juno’s 13 perijove) provided global coverage of Jupiter in thirteen narrow-band filters. These data sense stratospheric temperature (7.9 µm), tropospheric temperature via the collision-induced hydrogen-helium continuum (13, 17.6, 18.6, 19.5 µm), aerosol opacity (8.6 and 8.9µm), and the distribution of ammonia gas (10.5, 10.7 and 12.3 µm). These wavelengths primarily sound the upper troposphere at p < 0.7 bar, above the cloud tops, so are sensitive to the upper cell of the belt/zone Ferrel-like circulations. By stacking the data in all 13 filters, we invert the data using the optimal-estimation retrieval algorithm NEMESIS (Irwin et al., 2008) to derive temperature, aerosol and chemical structure over the whole planet. Meridional gradients of temperature, wind shear (derived from thermal balance equation) and chemical species will be examined to understand the upper-tropospheric circulation cells.
We confirm that the pattern of cool anticyclonic zones and warm cyclonic belts persists throughout the mid-latitudes, up to the boundary of the polar domains. This implies, via thermal wind balance, the decay of the zonal jets as a function of altitude throughout the upper troposphere. Aerosol opacity is often (but not always) highest in the anticyclonic zones, suggesting condensation of saturated vapours, but we caution that aerosol opacity is not a good proxy for atmospheric circulation on any giant planet. The thermal and compositional gradients derived from the VISIR maps are consistent with those from Voyager and Cassini, but opposite to what would be inferred for the Ferrel-like circulations of the deeper cell of Duer et al., (2021), which was suggested by Fletcher et al., (2021) to exist only below the water-cloud layer based on Juno microwave observations.
Concerning the Jovian polar regions, the analysis of VISIR imaging shows a large region of mid-infrared cooling poleward ~67˚S, co-located with the reflective aerosols observed in methane-band imaging by JunoCam, suggesting that they play a key role in the radiative cooling at the poles, and that this cooling extends from the upper troposphere into the stratosphere. These VISIR observations also reveal thermal contrasts across polar features, such as numerous cyclonic and anticyclonic vortices, as well as evidence of high-altitude heating by auroral precipitation. Comparison of zonal mean thermal properties and high-resolution visible imaging from Juno allows us to study the variability of atmospheric properties as a function of altitude and jet boundaries, particularly in the cold southern polar vortex.
Predetermining Atmospheric Parameters of Jupiter, in Order to Simplify Cloud Structure
Charlotte Alexander
The current atmospheric cloud models of Jupiter typically consist of a 3 cloud model, with varying methods of chromophore (cloud colouring compound) distribution, accompanied by a main cloud layer and a haze. There are a lot of unknown parameters which have to be chosen for these atmospheric set ups which often lead to large variations of the retrieved values across the disc and with subsequent observations. Using the two viewing angle method of [1], we were able to show that the model of [2] was unable to fit the model to the larger viewing angle simultaneously with the nadir as effectively as for a single viewing angle. Therefore in this work we are attempting to produce a model which able to fit the two angle spectra comparatively or better, but has been derived in a way that reduces some of the unknowns before the retrieval.
We were able to constrain the main cloud pressure and thickness using the techniques outlined in [3], using small wavelength range retrievals with only variable cloud density at all pressures. As this method was sensitive to the regions where cloud is present it indicates the location of all clouds in the model pressure range. Expansion of this technique across the Jovian disc has allowed us to infer a uniform main cloud pressure for all latitudes in the study (50°S-50°N).
Therefore, now with a fixed parameter retrieved beforehand, we are able to run retrievals whilst reducing some of the degeneracy that is typical in this problem. Retrievals are then being run for two viewing angle spectra simultaneously, fitting for other parameters including the refractive imaginary index using the Non-Linear Optimal Estimator for Multivariate Spectral Analysis (NEMESIS) algorithm [4]. Utilising observations from other years we are then able to test the robustness of this atmospheric set up, seeing how it adapts to the potential structural changes linked to the change of the visible cloud tops between observations. Therefore this work will detail the steps undertaken and the models retrieved in order to reduce some of the degeneracy in the atmospheric modelling of Jupiter at no expense to the atmospheric fit retrieved.
[1] Pérez-Hoyos, et al., (2020), Icarus, 352:114031 [2] Braude, et al., (2020), Icarus, 338:113589 [3] Irwin, et al., (2008), JQSRT, 109:1136–1150 [4] Irwin, et al., (2022), JGR:Planets, 127, e2022JE007189
JWST Mid-Infrared observations of Jupiter’s Great Red Spot: Preliminary Results
Jake Harkett
Observations of Jupiter’s Great Red Spot (GRS) took place in July and August 2022 as part of guaranteed-time Jovian observations (cycle 1 – GTO 1246). The GRS was a challenging target for the MIRI Medium Resolution Spectrometer (MRS) to probe. Jupiter’s rapid rotation resulted in an observing geometry that constantly changed from exposure to exposure. Also, the MRS fields of view are so small that only regional phenomena could be observed, not the entire Jovian disc. Worse, the full MRS spectral range could not be fully utilised as saturation occurred beyond 11 µm. Despite these shortcomings, the ability to probe mid-IR spectral ranges from 5-11 µm, including the first ever mapping of the GRS in the 5.5-7.7 µm region will enable the determination of 3D temperatures, thermal winds, atmospheric stability, gaseous composition, dynamics and aerosol distribution in unprecedented detail. In time this may answer questions about the GRS’s longevity and driving mechanisms, both of which are poorly understood.
The MIRI spectral maps sampled the top half of the anticyclone above the vortex midplane, enabling probing of the low temperatures, elevated aerosols, and elevated gaseous abundances that persist within the vortex (Fletcher et al., doi: 10.1016/j.icarus.2010.01.005). We derived the vertical aerosol and gaseous structure throughout the 1 mbar (using 7-8 μm spectra) to 5 bar range (using 5-6 μm spectra), complementing the Juno mission investigation of the depth of the GRS at higher pressures (Bolton et al., doi: 10.1126/science.abf1015). The newly inferred properties of the GRS in both the July and August epochs were acquired alongside simultaneous VLT/VISIR observations. This close connection with ground-based facilities allowed us to better understand the dynamics of this anticyclone and its interaction with the surrounding Southern Equatorial Belt and Zone. The saturated data was also split into shorter integration periods through alteration of the exposure settings to recover some saturated regions of the spectrum, enabling analysis of the ethane and acetylene emission features beyond 11 µm.
These GRS observations are part of a wider programme of JWST giant planet atmosphere observations, including complementary NIRSPEC (1.6-5.3 μm) mapping of the vortex at shorter wavelengths (ERS 1373) as well as global spatial and temporal context mapping by both IRTF/TEXES and VLT/VISIR. In this presentation we will: (i) summarise the science goals of GTO 1246, (ii) discuss the mapping and calibration techniques applied to this data and (iii) present the preliminary results from these observations.
Searching for a Runaway Greenhouse Scenario on Titan
Daniel Williams
Whilst the runway greenhouse effect has been investigated on both Earth and Venus, less research appears to have been focused on Titan, despite the presence of its thick moist atmosphere. Using a line-by-line radiation code, we aim to explore whether there are any feasible scenarios where Titan could enter a runaway state in the distant future.
Mid-Infrared Observations of Uranus and Neptune: A Turning Point
Michael T. Roman
Among the most intriguing about least explored bodies and planetary science, Uranus and Neptune are particularly challenging targets in the infrared due to their cold temperatures and great distances. Twenty years ago, we didn’t have a single spatially resolved image of Uranus or Neptune in the mid-infrared, but we are now approaching a turning point. With a growing number of improving observations and the advent of the JWST, we are on the cusp of truly characterising these planets in the infrared, revealing their trends in time and leading to new questions on what processes shape these mysterious outer worlds. In this talk, I shall review recent observations of the Ice Giants at mid-infrared wavelengths and look ahead to forthcoming observations with JWST.
Mushball in General Circulation Model: Parameterization of Water-ammonia Hail on Jupiter
Xinmiao Hu
Recent Juno microwave observations revealed some puzzling features of the ammonia distribution. In particular, an ammonia-poor layer extends down to levels of tens of bars in Jupiter outside the equatorial region to at least ±40° [Li et al. 2017]. Such a depletion has not yet emerged in general circulation models (GCMs). Guillot et al. [2020] showed that ammonia vapour can dissolve in water ice within violent storms, forming ammonia-rich hail, or “mushballs”, that leads to an efficient transport of ammonia to the deeper atmosphere and hence its observed depletion. Later it has been suggested that such a mechanism is more efficient on Neptune and Uranus, therefore responsible for the ammonia depletion observed in them. However, this mechanism has not been tested in numerical simulations in which convective events are self-consistently determined.
We present a simple parameterization scheme for the mushball process. Our scheme determines the mushball concentration using the water-ammonia equilibrium phase diagram and considers the transport of water and ammonia due to its associated downdraft. We implemented this scheme to a GCM based on the MITgcm [Young et al. 2019] that includes the following key parameterizations: a simple cloud microphysics model for water and ammonia, a water moist convection scheme that advects ammonia as a passive tracer, a dry convection scheme, and a two-stream radiative transfer scheme. We present our preliminary results using a two-dimensional setup of the aforementioned GCM, which produces an ammonia depletion similar to the Juno observation. Further, we explore the importance of different parameters in shaping the ammonia distribution on Jupiter.