Poster presentations and abstracts

On October 31, 2009, the Photodetector Array Camera and Spectrometer (PACS) onboard the Herschel Space Observatory observed far infrared (FIR) spectra of Jupiter in the wavelength range between 55 and 210 µm in the framework of the program ‘Water and Related Chemistry in the Solar System’ [Hartogh et al., 2009]. We aim at inferring the abundances of the trace constituents and the atmospheric temperature profile using these data, a line-by-line radiative transfer tool [Villanueva et al. 2018] and the least-squares fitting technique. Early model preparations and an earlier presentation of the preliminary spectra are given in Sagawa et al. [2010a,b]. Now, we present a more comprehensive data analysis. The spectra’s spectral resolution (R=λ/Δλ) depends on wavelength and grating order of the measurements and ranges from 990 to 5500. However, the effective spectral resolution was determined using detected, but unresolved spectral lines of stratospheric water, and varies between 1000 and 3000. Strong spectral features of methane (CH₄), ammonia (NH₃) and phosphine (PH₃) are clearly visible in the data (see fig. 1). Features from other species, such as water, hydrogen deuteride (HD), hydrogen sulfide (H₂S) and some hydrogen halides, such as hydrogen chloride (HCl), are also present in the data and might be used to retrieve upper limits for the relative abundances of these species. We assume a constant CH₄ abundance due to vertical mixing and the lack of methane cloud condensation. Inferring atmospheric parameters from compositional measurements will not only help to characterize the atmosphere of Jupiter but will also contribute to a better understanding of a plethora of physicochemical processes in the atmosphere.

Figure 1: PACS spectrum of Jupiter, expressed in line-to-continuum ratios. Coloured dots indicate the signatures attributable to different molecules in the atmosphere.

References:

Hartogh, P., Lellouch, E., Crovisier, J., Banaszkiewicz, M., Bensch, F., Bergin, E. A., ... & Blommaert, J. (2009). Water and related chemistry in the solar system. A guaranteed time key programme for Herschel. Planetary and Space Science, 57(13), 1596-1606.

Sagawa, H., Hartogh, P., Rengel, M., de Lange, A., & Cavalié, T. (2010a). Preparation for the solar system observations with Herschel: Simulation of Jupiter observations with PACS. Planetary and Space Science, 58(13), 1692-1698.

Hideo Sagawa, P. Hartogh, E. Lellouch, H. Feuchtgruber, G. Orton, et al. (2010b) Far Infrared Spectra of Jupiter Observed with PACS Onboard Herschel. American Astronomical Society, DPS meeting #42, 11/31/2010, Pasadena, CA, United States.

Villanueva, G. L., Smith, M. D., Protopapa, S., Faggi, S., & Mandell, A. M. (2018). Planetary Spectrum Generator: An accurate online radiative transfer suite for atmospheres, comets, small bodies and exoplanets. Journal of Quantitative Spectroscopy and Radiative Transfer, 217, 86-104.

How to cite: Gapp, C., Rengel, M., Hartogh, P., Sagawa, H., Feuchtgruber, H., and Lellouch, E.: Retrieval of Jupiter’s atmospheric parameters using far infrared spectra measured with PACS onboard the Herschel Space Observatory, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-152, https://doi.org/10.5194/epsc2020-152, 2020.

Jupiter, Saturn and Uranus have non-auroral ionospheres that are measurably 100s of Kelvin hotter than models can explain by solar heating alone. This problem has existed for many decades and is generally termed in literature as the "energy crisis". One way to cause heating in the non-auroral ionosphere is to redistribute heat from the auroral ionosphere at the poles down to lower latitudes (the auroral region itself is heated thermally by collisions as a result of the auroral mechanism). Most models of global circulation suggest that heat within the polar/auroral is confined there by Coriolis forces, such that auroral energy cannot be communicated to lower latitudes, but until now there have been no high spatial resolution observations of temperature in the auroral region simultaneous with non-auroral regions to confirm it. Today we will present ground-based observations of Jupiter's ionospheric H3+ temperature at high spatial resolution (~1000km per pixel). H3+ is a major ion at Jupiter, considered in quasi-thermodynamic equilibrium with its surroundings, and therefore a good proxy for energy balance of the ionosphere. These observations, taken by the 10-meter Keck telescope on April 14, 2016 and Jan 25, 2017, strongly suggest heat from the auroral region is spreading to lower latitudes, such that the missing heat source causing the "energy crisis" may ultimately be auroral in nature.

How to cite: O'Donoghue, J., Moore, L., Melin, H., and Stallard, T.: Observational evidence for heat transfer from Jupiter's polar auroral region to lower latitudes, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-693, https://doi.org/10.5194/epsc2020-693, 2020.

In 1979, the Voyager spacecraft arrived at Jupiter. Amongst their rich array of discoveries, they identified bright bursts of radio emission at kHz frequencies¹, often called quasi-periodic (QP) bursts, and discovered Jupiter’s ultraviolet (UV) aurora² - the most powerful aurora in the Solar System³. The same year that the Voyager spacecraft explored the Jovian system, the Einstein X-ray Observatory took the first X-ray images of Jupiter⁴ and discovered that planets can also produce bright and dynamic X-ray aurora^5,6. Over the subsequent decades, these distinct multi-waveband emissions have all been observed to pulse with quasi-periodic regularity^7–10. Here, we combine simultaneous observations by the Juno spacecraft with the X-ray and UV observatories: XMM-Newton, Chandra and the Hubble Space Telescope. These observations show that the radio, UV and X-ray pulses are all synchronised, beating in time together. Further, they reveal that the X-ray and radio pulses share an identical 42.5 minute periodicity with simultaneously measured compression-mode Ultra Low Frequency (ULF) waves in Jupiter’s outer magnetosphere¹¹. ULF waves are known to modulate wave-particle interactions that can cause electron and ion precipitation, providing a physically consistent explanation for the observed simultaneous ion and electron emissions.  The unification of Jupiter’s X-ray, UV and radio pulsations and their connection to ULF waves provides fundamental and potentially universal insights into the redistribution of energy in magnetised space environments.

How to cite: Dunn, W., Yao, Z., Woodfield, E., Sulaiman, A., Kurth, W., Grodent, D., Elliott, S., Hospodarsky, G., Imai, M., Wibisono, A., Weigt, D., Kotsiaros, S., Branduardi-Raymont, G., Clark, G., Bonfond, B., Haewsantati, K., Rae, I. J., Manners, H., Rodriguez, P., and Ness, J.-U. and the William Dunn: Connecting Jupiter's Auroral Pulsations with In-situ Measurements by Juno, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-864, https://doi.org/10.5194/epsc2020-864, 2020.

In this presentation, we exploit the charge-dependent nature of field-aligned potentials in Jupiter’s polar cap auroral region to infer the charge states of energetic oxygen and sulfur. To-date, there are very limited and sparse measurements of the > 50 keV oxygen and sulfur charge states, yet many studies have demonstrated their importance in understanding the details of various physical processes, such as, X-ray aurora, ion-neutral interactions in Jupiter’s neutral cloud and particle acceleration theories. In this contribution, we develop a technique to determine the most abundant charge states associated with heavy ions in Jupiter’s polar magnetosphere. We find that O⁺ and S⁺⁺ are the most abundant and therefore iogenic in origin. The results are important because they provide 1) strong evidence that soft X-ray sources are likely due to charge stripping of magnetospheric ions and; 2) a more complete spatial map of the oxygen and sulfur charge states, which is important for understanding how the charge- and mass-dependent physical processes sculpt the energetic particles throughout the Jovian magnetosphere. 

How to cite: Clark, G., Mauk, B., Kollmann, P., Paranicas, C., Bagenal, F., Allen, R., Bingham, S., Bolton, S., Cohen, I., Ebert, R., Dunn, W., Haggerty, D., Houston, S., Jackman, C., Roussos, E., and Rymer, A.: Heavy ion charge states in Jupiter’s polar magnetosphere inferred from auroral megavolt electric potentials, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-902, https://doi.org/10.5194/epsc2020-902, 2020.

The Juno spacecraft has been orbiting Jupiter since July 2016 providing stunning new information about the planet and its environment. The new magnetic field model, JRM09, with much improved accuracy near the planet, provides the basis for a better understanding of Io-related decametric radio emissions and implications for auroral processes. Here, we study Io-related DAM events observed by the Juno Waves instrument to estimate the beaming angle, the resonant electron energy and radio source location by forward modeling. The JRM09 magnetic field model is used to better constrain the location and observability of the radio emissions, and characterize the loss cone-driven electron cyclotron maser instability. We obtained good agreement between synthetic and observed arcs. The estimated beaming cone half-angles range from 33° to 85° and the obtained resonant electron energies are up to 23 times higher than previously proposed. Additionally, we quantitatively analyze the higher likelihood of observing groups of arcs originating in the northern hemisphere relative to those originating in the southern hemisphere. This is primarily a consequence of the asymmetry of the magnetic field geometry, observer location, and pitch angles of the electrons at the equator.  

How to cite: Martos, Y. M., Imai, M., Connerney, J. E. P., Kotsiaros, S., and Kurth, W. S.: Juno reveals new insights into Io-related decameter radio emissions, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-441, https://doi.org/10.5194/epsc2020-441, 2020.

The dynamics of the Jovian magnetosphere is controlled by the complex interplay of the planet’s fast rotation, its solar-wind interaction and its main plasma source at the Io torus. Juno observations have amply demonstrated that the Magnetosphere-Ionosphere-Thermosphere (MIT) coupling processes and regimes which control this interplay are significantly different from their Earth and Saturn counterparts. At the ionospheric level, these MIT coupling processes can be characterized by a set of key parameters which include ionospheric electrodynamic parameters (conductances, currents and electric fields), exchanges of particles along field lines and auroral emissions. Knowledge of these key parameters in turn makes it possible to estimate the net deposition/extraction of momentum and energy into/out of the Jovian upper atmosphere. We will present a method combining Juno multi-instrument data (MAG, JADE, JEDI, UVS, JIRAM and WAVES), adequate modelling tools (the TRANSPLANET ionospheric dynamics model and a simplified set of ionospheric current closure equations) and the AMDA data handling tools to provide preliminary estimates of these key parameters and their variation along the ionospheric footprint of Juno’s magnetic field line and across the auroral ovals for three of the first perijoves of the mission. We will discuss how this synergistic use of data and models can also contribute to provide a better determination of poorly known parameters such as the vertical structure of the auroral and polar Jovian neutral atmosphere.

How to cite: Blanc, M., Wang, Y., Andre, N., Blelly, P.-L., Louis, C., Marchaudon, A., Gerard, J.-C., Bonfond, B., Grodent, D., Dinelli, B. M., Adriani, A., Mura, A., Mauk, B., Clark, G., Allegrini, F., Bolton, S., Gladstone, R., Connerney, J., Kotsiaros, S., and Kurth, W.: A preliminary study of Magnetosphere-Ionosphere-Thermosphere coupling key parameters at Jupiter Based on Juno multi-instrument data and modelling tools, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-979, https://doi.org/10.5194/epsc2020-979, 2020.

Background: The magnetopause (MP) boundary is formed by the solar wind plasma flow interacting with a planetary magnetic field. Magnetic reconnection is an important process at this boundary as it energises plasma via release of magnetic energy. Reconnection of the IMF and internal magnetic field of the planet produces an “open” magnetosphere allowing solar wind and magnetosheath particles to directly enter the magnetosphere. At Saturn, the nature of MP reconnection remains unclear. Masters et al. (2012) hypothesised that viable reconnection under a large difference in plasma β across the MP also requires a high magnetic shear (i.e. magnetic fields either side of the boundary close to anti-parallel).

Objective: The current study uses bulk electron heating at MP crossings (‘events’) as a reconnection signature to test the following hypotheses, suggested by the study of Masters et al. (2012). 1) Events where the boundary is locally closed would have essentially no observed temperature change, whereas most events with locally open boundary should have observed change close to the theoretical prediction. 2) Events with evidence of plasma energization should be in the ‘reconnection possible’ regime, whereas those without such evidence should be in the ‘reconnection suppressed’ regime.

Methods: We analysed 70 MP crossings made by the Cassini spacecraft from April 2005 to July 2007, previously reported by Masters et al. (2012). These 70 events have a determined plasma β on both sides of the MP. Magnetic field and particle data were used to characterize the crossings. The bulk temperature was determined using three different methods, related to properties of the observed energy distribution (including methods from Lewis et al. 2008). We compared the observed heating of magnetosheath electrons with the prediction based on reconnection, using the semi-empirical relationship proposed by Phan et al. (2013) which relates the degree of bulk electron heating to the inflow Alfven speed.

Results: Plots of observed versus predicted electron temperature change for all 70 crossings showed that there is positive correlation between the two when the 1d moment method (Lewis et al. 2008) was used to calculate heating (Figure 1). We do see a tendency of better agreement with prediction for the locally ‘open’ boundary cases based on the threshold  Bn/B >= 0.1 for the minimum variance component of the magnetic field. For the case of locally ‘closed’ boundary (Bn/B < 0.1), we observe a cluster of points near dT=0, but also numerous cases of significant heating. We find five cases where the observed heating exceeds prediction significantly (>3eV). These results suggest that although a large portion of events fit our hypothesis 1 within uncertainty, there are some which do not. Based on the magnetic shear measured locally by the spacecraft either side of the MP, we find 81% of events with no energisation were situated in the ‘reconnection suppressed’ regime, and 43% of events with energization lay in the ‘reconnection possible’ regime (Figure 2). These results support hypothesis 2 to some extent.

Conclusion:

A statistical study of observed and theoretical electron bulk heating was performed at the magnetopause based on 70 magnetopause crossings detected by the Cassini spacecraft. Our results support both hypotheses 1 and 2 to some extent. One reason why some events do not fit our hypotheses is because we are assuming local conditions to be indicative of the putative reconnection site. However, the spacecraft could be quite distant from this site, and still magnetically connected to it. Another reason is temporal variability in the near-magnetopause environment. We plan to analyse the dataset further in future work, by taking these aspects into account.

Figure 1 (Left): Observed against predicted bulk electron temperature change for all 70 crossings. First column: Heating based on 3d moment method for full energy distribution. Second column: Heating based on 3d moment method for the cold energy distribution. Third column: Heating based on 1d moment method for the peak of the energy distribution. Top panels: locally ‘closed’ boundary based on threshold Bn/B < 0.1. Bottom panels: locally ‘open’ boundary based on threshold Bn/B > 0.1. Red markers: Steady transitions with field rotation. Green markers: Turbulent transitions with field rotation. Blue markers: Transitions without field rotation.

Figure 2 (Right):  Assessment of diamagnetic suppression of reconnection using the 70 MP crossings. Colour represents observed heating using 1d moment method. The solid curve corresponds to a current sheet thickness L = 1 d_i, and the dashed curves on the left and right of it correspond to L = 0.5 d_i and L = 2 d_i, respectively. ‘x’ markers: Steady transitions with field rotation. ‘o’ markers: Turbulent transitions with field rotation. ‘v’ markers: Transitions without field rotation.

How to cite: Cheng, I. K., Achilleos, N., Masters, A., Lewis, G., and Kane, M.: Electron Heating at Saturn's Magnetopause, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-1016, https://doi.org/10.5194/epsc2020-1016, 2020.

Observations of energetic neutral atoms (ENAs) are a useful tool for analyzing ion and neutral abundances in planetary magnetospheres. Saturn's magnetosphere is dominated by high densities of water group neutrals which originate from the icy moon Enceladus and are confined close to the equatorial plane due to the planet's rapid rotation rate. Hot plasma populations are mainly created by magnetotail reconnection events and driven inward with the subsequent magnetic field dipolarization to form a so-called "injection". As this hot plasma interacts with the ambient neutral population, charge exchange creates ENAs whose motion is not governed by the magnetic field anymore, such that they can be observed remotely allowing us to image Saturn's ring current on a global scale.

Over the course of the Cassini mission, the Ion Neutral Camera (INCA) of the Magnetosphere Imaging Instrument (MIMI) collected vast amounts of hydrogen and oxygen ENA observations of Saturn's magnetosphere from a variety of different viewing geometries. In order to enable statistical investigations of the morphology and dynamics of Saturn's ring current, it is useful to re-bin and re-project the camera-like views from the spacecraft-based perspective into a common reference frame.

We developed an algorithm which projects ENA observations by the MIMI-INCA instrument into a regular grid in Saturn's equatorial plane, spanning from -30 to +30 Saturn radii in the X_KSMAG and Y_KSMAG axes of the Kronocentric Solar Magnetic (KSMAG) reference frame with a resolution of 2 pixels per Saturn radii. With most neutrals and ions being confined into an equatorial rotating disc, this projection is quite accurate in both spatial location and measured ENA intensity, provided the spacecraft is located at large enough perpendicular distances from the equatorial plane such that the viewing angle is not too flat. 

The INCA dataset can exhibit several different kinds of contamination: sunlight entering the detector may lead to artificial intensifications, and bit errors during data transmission may result in wrong count numbers. High ENA fluxes may exceed the limit up to which the instrument calibration is valid, and energetic ion beams bypassing the high voltage deflector and entering the detector may lead to artifacts not representing the actual ENA intensity. Many of these events have been identified by the instrument team and tables are available with INCA calibration files, but ion contamination events were so far not identified - we developed an algorithm identifying these to complement previous exclusion lists.

Our dataset of projections includes all days during which Cassini was located at >4 R_S off the equatorial plane, and will be provided as a zip archive of daily files in .fits format. A Python routine for loading these files into a useful array format will be provided, returning not only ENA intensity data but also various geometric information detailing the spacecraft's location as well as data quality flags. This allows the user to easily set validity constraints depending on the spacecraft distance from and elevation above each pixel and highlights which exposures may be contaminated.

The resulting dataset is a good foundation for investigating the statistical properties of Saturn's ring current as well as its complicated dynamics in relation to other remote and in situ observations of, for example, auroral emissions and magnetotail reconnection events.

How to cite: Bader, A., Kinrade, J., Badman, S. V., Paranicas, C., Constable, D. A., and Mitchell, D. G.: Towards a complete dataset of equatorial projections of Saturn's ENA emissions observed by Cassini/INCA, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-300, https://doi.org/10.5194/epsc2020-300, 2020.

The effects of the solar wind on Saturn’s magnetosphere are poorly constrained as there are no consistent solar wind monitors upstream of the planet. This has limited previous studies of the solar wind’s influence on the Saturnian magnetosphere to case studies and time dependant analyses of intervals of the Cassini data. While useful and enlightening, these methods assume a priori, a relationship between the solar wind and magnetospheric driving or are biased due to their selection based on particular events detected within the magnetosphere.  

Mutual information is a measure of information gain and is measured by the change in uncertainty, after the reception of an input variable in relation to a related output variable. The more mutual information in a system between two variables, the stronger the relationship between the two. We apply Mutual Information Theory to investigate the statistical relationship between solar wind parameters e.g. density, magnetic field strength, velocity, and magnetospheric driving. We consider the entire Cassini dataset, identifying intervals where the Tao et al. [2005] solar wind propagation model is valid. This robust statistical analysis determines magnetospheric proxies for the solar wind and, crucially, how much information these proxies provide about the state of the solar wind. Finding and confirming the relation of these indirect proxies to solar wind propagation models presents the opportunity to open long time scale data to interpretation with respect to the solar wind’s behaviour at the outer planets, using data from past missions. Initial results indicate that the direction of the IMF plays a stronger role in driving Saturn’s magnetosphere than previously thought and identifies potentially new solar wind parameters that effect Saturn’s magnetosphere. 

How to cite: Gould, W., Ray, L., and Arridge, C. S.: Deciphering the Solar Wind at Saturn, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-771, https://doi.org/10.5194/epsc2020-771, 2020.