Europa is also spotted to have the water outgassing activities, similar to those plumes of Enceladus associated with its subsurface ocean, by the space and ground telescopes as well as reinvestigating the Galileo data (Roth et al., 2014; Sparks et al., 2016, 2017; Paganini et al., 2020; Jia et al., 2018; Arnold et al., 2019; Huybrighs et al., 2020). In this work, we use a 3D Direct Simulation Monte Carlo (DSMC) model to study the plume structures of Europa (i.e., Lai et al., 2019). This model can describe the gas plumes with a broad flow regime ranging from close to continuum near the surface to free-molecular condition at higher altitudes. With a systematic study of a large parametric space of the total gas production rate and initial gas ejection velocity, the gas number density, temperature and velocity information of outgassing activity at various scales can be derived. In addition, the modeling results will be incorporated with a n-LTE radiative transfer model to simulate the water plume morphology which could be observed in the sub-millimeter and millimeter wavelengths. Understanding the plume of Europa and its effects (i.e., icy dust deposit on surface) plays a key role to probe its interior structure and outgassing mechanism (i.e., cryovolcanism). Our results can be well prepared for the space and ground telescope observations (i.e., ALMA) and the in-situ measurements of the future spacecraft missions such as JUICE and Europa Clipper.

Magnetic fields induced in the oceans of icy moons can be used to characterize the properties of the oceans. The Galileo spacecraft measured induced fields from extraterrestrial oceans—in Europa and possibly Ganymede and Callisto—but only placed weak constraints on the thickness and salinity of the oceans. We explore the parameter space of ocean thickness and composition, and corresponding induction response at multiple periods of the externally imposed fields, for self-consistent structures of Jupiter's large icy moons, and for the inner 3 large icy moons of Uranus. Modeled induction responses published to date have been limited to nested concentric conducting shells and have neglected motional induction. We will describe recent work examining effects due to deviations from spherical symmetry and secondary magnetic fields induced by fluid flows within the oceans. This work will be aid in planning and interpretation of magnetic investigations of Jupiter's moons by the Europa Clipper and JUICE missions, and by future missions exploring the moons of Uranus and Neptune’s moon Triton.

Giant planet upper atmospheres have long been observed to be significantly hotter than expected. Magnetosphere-atmosphere coupling processes give rise to auroral emissions and enormous energy deposition near the magnetic poles, explaining high temperatures for narrow regions of the planet. However, global circulation models have difficulty redistributing auroral energy globally due to the strong Coriolis forces and ion drag, particularly at Jupiter. Heating by solar photons is insufficient at giant planets, and yet other proposed processes, such as heating by waves originating from the lower atmosphere, also fail to explain the warm equatorial temperatures planet-wide. There remains no self-consistent explanation for measured non-auroral temperatures at present, mostly due to a lack of definitive observational constraints. Here, using high-resolution maps capable of tracing global temperature gradients at Jupiter, we show that upper-atmosphere temperatures decrease steadily from the aurora to the equator. During a period of enhanced auroral activity, likely driven by a coincident solar wind compression event, we also find a global increase in temperature accompanied by a high temperature planetary-scale structure that appears to emanate from the auroral region. These observations indicate that Jupiter's upper atmosphere is predominantly heated via the redistribution of auroral energy.

We present thermal imaging of Jupiter’s polar regions from the Subaru Telescope using the COoled Mid-Infrared Camera and Spectrometer (COMICS), between 7.8 and 25 μm that supplements the spectral capabilities of Juno’s instrumentation. These observations characterize the distinct thermal signatures of Jupiter’s north and south polar vortices, mapping temperatures in the upper troposphere and stratosphere, as well as constraining the distribution of tropospheric gases and condensate aerosols. The COMICS data cover 2005-2020, allowing an investigation of long-term trends, as well as comparisons with Juno and other Juno-supporting observations from 2016 onward. Analysis of zonally averaged COMICS data show that the north polar region exhibits a steep temperature decline of at least 2 K from the tropospheric midlatitude temperatures around 60°N-63°N (planetocentric) and a similar drop in temperatures more gradually over 54°S-64°S, with the exact latitude of the 2 K departure from midlatitude temperatures varying slightly between observations for both of the poles. No seasonal trends were observed. Away from regions affected by auroral-related heating, the boundaries of the vortex in the stratospheric temperature field appear to be similar to those in the troposphere, as stated above.  However, unlike the uniformly colder temperatures of the polar vortices in the troposphere, temperatures in the polar vortices in the stratospshere most often appear be the same or even warmer than lower latitudes, with the south polar region appearing warmer in 2016-2020 and the north polar region warmer in previous years.  The non-uniform boundaries of the polar vortices appear roughly coincident with the boundaries of distinct bodies of overlying hazes known as the polar caps, detected in reflected sunlight, suggesting similar dynamical boundaries defined by a Rossby wave. It also implies important contributions by these aerosols to the radiative balance within these polar regions.

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 microns in the framework of the program ‘Water and Related Chemistry in the Solar System’. 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 and the least-squares fitting and retrieval techniques.PACS’s spectral resolution depends on wavelength and grating order of the measurements and ranges from 990 to 5500 for point sources. However, the effective spectral resolution of the Jupiter measurements was determined using detected, but unresolved spectral lines of stratospheric water, and varies between 500 and 3800. The effective spectral resolution is generally lower for spatially resolved sources such as Jupiter mainly because of its brightness and fast rotation which induces Doppler broadening of the lines. Strong spectral features of methane, ammonia and phosphine are clearly visible in the data. Thanks to PACS' effective spectral resolution and sensitivity range, these lines were used to constrain the abundance profiles of NH3 and PH3 in their cloud condensing pressure ranges. We considered CH4 to be constant in altitude due to vertical mixing and the lack of methane cloud condensation. Features from other species, such as water and hydrogen deuteride are also present in the data and were used to retrieve the abundances of these species. 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. The results of our analysis will be useful for future observations of Jupiter, as, for instance, planned with the Sub-millimeter Wave Instrument (SWI) onboard JUICE.

In support of the Herschel Space Observatory and in the framework of the program “Water and Related Chemistry in the Solar System” [1], hydrogen cyanide (HCN) on Titan was observed from ground at submm wavelengths. We carried submm heterodyne spectroscopy observations of HCN (4-3) at 345.5 GHz with the Atacama Pathfinder EXperiment and the APEX 2 heterodyne receiver, and of HCN (3-2) at 265.9 GHz with the Institut de radioastronomie millimétrique (IRAM) 30-m telescope and the Heterodyne Receiver Array (HERA) receiver in Titan atmosphere. Observations were carried out on June 16, 2010, and March 19, 2011.We applied a line-by-line radiative transfer code to calculate the synthetic spectra, and a retrieval algorithm based on Optimal Estimation to retrieve the temperature and abundances. We calculated the mean abundance profile obtained from the four data-sets and quantified the differences in the mean values. We report here the data, our derived HCN profiles, comparisons between our results and the values from Herschel [3-4] acquired during 2010, and previous studies. Our derived HCN profiles are consistent with an increase from 40 ppb at ∼100 km to 4 ppm at ∼200 km. Measured HCN abundances on Titan with data acquired quasi simultaneously and different transitions exhibit similar abundance distributions. Beyond the intrinsic scientific interest, these observations proven their usefulness in supporting spacecraft observations of Solar System bodies, in particular, of Titan’s atmosphere. The mean measured HCN profile can be used as reference for future HCN studies of Titan and Titan-like exoplanets.
[1] Hartogh, P.; Lellouch, E.; Crovisier, J., et al. 2009, PSS, Volume 57, Issue 13, p. 1596-1606
[2] Rengel, M.; Sagawa, H.; Hartogh, P., et al. 2014, A&A, 561
[3] Courtin, R., Swinyard, B. M., Moreno, R., et al. 2011, A&A, 536, L2