On 27 August 2016, the Juno spacecraft acquired science observations of Jupiter, passing less than 5000 kilometers above the equatorial cloud tops. Images of Jupiter's poles show a chaotic scene, ...unlike Saturn's poles. Microwave sounding reveals weather features at pressures deeper than 100 bars, dominated by an ammonia-rich, narrow low-latitude plume resembling a deeper, wider version of Earth's Hadley cell. Near-infrared mapping reveals the relative humidity within prominent downwelling regions. Juno's measured gravity field differs substantially from the last available estimate and is one order of magnitude more precise. This has implications for the distribution of heavy elements in the interior, including the existence and mass of Jupiter's core. The observed magnetic field exhibits smaller spatial variations than expected, indicative of a rich harmonic content.
Ionospheric conductivity perpendicular to the magnetic field plays a crucial role in the electrical coupling between planetary magnetospheres and ionospheres. At Jupiter, it controls the flow of ...ionospheric current from above and the closure of the magnetosphere‐ionosphere circuit in the ionosphere. We use multispectral images collected with the Ultraviolet Spectral (UVS) imager on board Juno to estimate the two‐dimensional distribution of the electron energy flux and characteristic energy. These values are fed to an ionospheric model describing the generation and loss of different ion species, to calculate the auroral Pedersen conductivity. The vertical distributions of H3+, hydrocarbon ions, and electrons are calculated at steady state for each UVS pixel to characterize the spatial distribution of electrical conductance in the auroral region. We find that the main contribution to the Pedersen conductance stems from collisions of H3+and heavier ions with H2. However, hydrocarbon ions contribute as much as 50% to Σp when the auroral electrons penetrate below the homopause. The largest values are usually associated with the bright main emission, the Io auroral footprint and occasional bright emissions at high latitude. We present examples of maps for both hemispheres based on Juno‐UVS images, with Pedersen conductance ranging from less than 0.1 to a few mhos.
Plain Language Summary
One of the quantities characterizing the ability of ionospheres to carry currents perpendicular to the magnetic field is the altitude integrated Pedersen conductivity. On Jupiter, it is an important quantity that partly controls how electric currents can flow between the magnetosphere and the high‐latitude ionosphere. It is therefore a key element in the understanding of how and where the Jovian aurora is formed and an important input to numerical models of auroral precipitation. We use observations from the UltraViolet spectral imager near Juno's closest approach to Jupiter to remotely characterize the flux of energy carried by the auroral electrons and their mean energy. These quantities are evaluated for each instrumental pixel and used as inputs to a model to map the Pedersen integrated conductivity. The main contributions to the conductance are caused by collisions between H3+ and hydrocarbon ions such as CH5+ and C3Hn+ with neutral constituents. We present examples of Pedersen conductance maps for both hemispheres. We find that the conductance is spatially very variable with values ranging from less than 0.1 to several mhos. The largest values are usually associated with the bright main emission, the Io auroral footprint and occasional bright emissions at high latitude.
Key Points
Multispectral auroral observations from UVS‐Juno are used to map the auroral ionospheric Pedersen conductance in both hemispheres
H3+ and hydrocarbon ions make most of the contribution to auroral ionospheric conductance
The conductance varies from less than 0.1 up to several mhos in the main aurora, high latitude precipitation, and Io magnetic footprint
The global D/H ratio on Mars is an important measurement for understanding the past history of water on Mars; locally, through condensation and sublimation processes, it is a possible tracer of the ...sources and sinks of water vapor on Mars. Measuring D/H as a function of longitude, latitude and season is necessary for determining the present averaged value of D/H on Mars. Following an earlier measurement in April 2014, we used the Echelon Cross Echelle Spectrograph (EXES) instrument on board the Stratospheric Observatory for Infrared Astronomy (SOFIA) facility to map D/H on Mars on two occasions, on March 24, 2016 (Ls = 127°), and January 24, 2017 (Ls = 304°), by measuring simultaneously the abundances of H2O and HDO in the 1383–1391 cm−1 range (7.2 μm). The D/H disk-integrated values are 4.0 (+0.8, −0.6) × Vienna Standard Mean Ocean Water (VSMOW) and 4.5 (+0.7, −0.6) × VSMOW, respectively, in agreement with our earlier result. The main result of this study is that there is no evidence of strong local variations in the D/H ratio nor for seasonal variations in the global D/H ratio between northern summer and southern summer.
Context.
Since the 1950s, quasi-periodic oscillations have been studied in the terrestrial equatorial stratosphere. Other planets of the Solar System present (or are expected to present) such ...oscillations; for example the Jupiter equatorial oscillation and the Saturn semi-annual oscillation. In Jupiter’s stratosphere, the equatorial oscillation of its relative temperature structure about the equator is characterized by a quasi-period of 4.4 yr.
Aims.
The stratospheric wind field in Jupiter’s equatorial zone has never been directly observed. In this paper, we aim to map the absolute wind speeds in Jupiter’s equatorial stratosphere in order to quantify vertical and horizontal wind and temperature shear.
Methods.
Assuming geostrophic equilibrium, we apply the thermal wind balance using almost simultaneous stratospheric temperature measurements between 0.1 and 30 mbar performed with Gemini/TEXES and direct zonal wind measurements derived at 1 mbar from ALMA observations, all carried out between March 14 and 22, 2017. We are thus able to self-consistently calculate the zonal wind field in Jupiter’s stratosphere where the JEO occurs.
Results.
We obtain a stratospheric map of the zonal wind speeds as a function of latitude and pressure about Jupiter’s equator for the first time. The winds are vertically layered with successive eastward and westward jets. We find a 200 m s
−1
westward jet at 4 mbar at the equator, with a typical longitudinal variability on the order of ~50 m s
−1
. By extending our wind calculations to the upper troposphere, we find a wind structure that is qualitatively close to the wind observed using cloud-tracking techniques.
Conclusions.
Almost simultaneous temperature and wind measurements, both in the stratosphere, are a powerful tool for future investigations of the JEO (and other planetary equatorial oscillations) and its temporal evolution.
Context. The circumstellar ammonia (NH3) chemistry in evolved stars is poorly understood. Previous observations and modelling showed that NH3 abundance in oxygen-rich stars is several orders of ...magnitude above that predicted by equilibrium chemistry. Aims. We would like to characterise the spatial distribution and excitation of NH3 in the oxygen-rich circumstellar envelopes (CSEs) of four diverse targets: IK Tau, VY CMa, OH 231.8+4.2, and IRC +10420. Methods. We observed NH3 emission from the ground state in the inversion transitions near 1.3 cm with the Very Large Array (VLA) and submillimetre rotational transitions with the Heterodyne Instrument for the Far-Infrared (HIFI) aboard Herschel Space Observatory from all four targets. For IK Tau and VY CMa, we observed NH3 rovibrational absorption lines in the ν2 band near 10.5 μm with the Texas Echelon Cross Echelle Spectrograph (TEXES) at the NASA Infrared Telescope Facility (IRTF). We also attempted to search for the rotational transition within the excited vibrational state (v2 = 1) near 2 mm with the IRAM 30m Telescope. Non-LTE radiative transfer modelling, including radiative pumping to the vibrational state, was carried out to derive the radial distribution of NH3 in the CSEs of these targets. Results. We detected NH3 inversion and rotational emission in all four targets. IK Tau and VY CMa show blueshifted absorption in the rovibrational spectra. We did not detect vibrationally excited rotational transition from IK Tau. Spatially resolved VLA images of IK Tau and IRC +10420 show clumpy emission structures; unresolved images of VY CMa and OH 231.8+4.2 indicate that the spatial-kinematic distribution of NH3 is similar to that of assorted molecules, such as SO and SO2, that exhibit localised and clumpy emission. Our modelling shows that the NH3 abundance relative to molecular hydrogen is generally of the order of 10−7, which is a few times lower than previous estimates that were made without considering radiative pumping and is at least ten times higher than that in the carbon-rich CSE of IRC +10216. NH3 in OH 231.8+4.2 and IRC +10420 is found to emit in gas denser than the ambient medium. Incidentally, we also derived a new period of IK Tau from its V-band light curve. Conclusions. NH3 is again detected in very high abundance in evolved stars, especially the oxygen-rich ones. Its emission mainly arises from localised spatial-kinematic structures that are probably denser than the ambient gas. Circumstellar shocks in the accelerated wind may contribute to the production of NH3. Future mid-infrared spectroscopy and radio imaging studies are necessary to constrain the radii and physical conditions of the formation regions of NH3.
We characterize the precipitating electrons accelerated in the Europa‐magnetosphere interaction by analyzing in situ measurements and remote sensing observations recorded during 10 crossings of the ...flux tubes connected to Europa's auroral footprint tail by Juno. The electron downward energy flux, ranging from 34 to 0.8 mW/m2, exhibits an exponential decay as a function of downtail distance, with an e‐folding factor of 7.4°. Electrons are accelerated at energies between 0.3 and 25 keV, with a characteristic energy that decreases downtail. The electron distributions form non‐monotonic spectra in the near tail (i.e., within an angular separation of less than 4°) that become broadband in the far tail. The size of the interaction region at the equator is estimated to be 4.2 ± 0.9 Europa radii, consistent with previous estimates based on theory and UV observations.
Plain Language Summary
The space environment close to Jupiter is dominated by the magnetic field of the giant planet in a so‐called magnetosphere. The four Galilean moons, including Europa, orbit deep inside the Jovian magnetosphere and therefore constantly interact with the rapidly rotating plasma flow made of charged particles trapped by the magnetic field of the giant planet. The interaction between moons and plasma generates electromagnetic waves, accelerate particles and produce emissions at various wavelengths, including bright UV auroral spots and tails in the atmosphere of Jupiter. In this work, we present 10 events where the Juno spacecraft observed both in situ and remotely the acceleration of electrons due to the interaction between the icy moon Europa and the magnetospheric environment. We characterize the properties of the accelerated electrons. In particular, we find that acceleration is maximum near the moon itself, and that two distinct families of electron distributions exist.
Key Points
Juno unambiguously observed 10 events of downward electron acceleration from Europa at various downtail separations with the moon
Precipitating energy fluxes decrease exponentially as a function of downtail distance from the moon, with an e‐folding of 7.4°
Two types of electron distributions exist: non‐monotonic in the near tail and broadband in the far tail
We report the first in situ observations of electron measurements at a Europa footprint tail (FPT) crossing in the auroral region. During its 12th science perijove pass, Juno crossed magnetic field ...lines connected to Europa's FPT. We find that electrons in the range ~0.4 to ~25 keV, with a characteristic energy of 3.6 ± 0.5 keV, precipitate into Jupiter's atmosphere to create the footprint aurora. The energy flux peaks at ~36 mW/m2, while the peak ultraviolet (UV) brightness is estimated at 37 kR. We estimate the peak electron density and temperature to be 17.3 cm−3 and 1.8 ± 0.1 keV, respectively. Using magnetic flux shell mapping, we estimate that the radial width of the interaction at Europa's orbit spans roughly 3.6 ± 1.0 Europa radii. In contrast to typical Io FPT crossings, the instrument background caused by penetrating energetic radiation (> ~5–10 MeV electrons) increased during the Europa FPT crossing.
Plain Language Summary
Jupiter's moons interact with Jupiter's space environment, or magnetosphere, and create auroral spots and tails in Jupiter's ionosphere. Io's aurora footprint on Jupiter is the strongest and most persistent of all moons, but Ganymede, Callisto, and Europa's auroral footprints are also routinely observed by remote platforms. NASA's Juno mission and its instrument suite occasionally fly through regions that are connected to the moon‐magnetosphere interactions. During these crossings, Juno samples the electrons and ions that create the aurora. This paper is the first report of electron measurements taken during a Juno crossing of Europa's tail. These measurements confirm previous results based on remote observations. Most importantly, they provide a sample of the conditions in the regions associated with Europa's footprint aurora in Jupiter's magnetosphere.
Key Points
This is the first report of in situ electron measurements of a Europa footprint tail crossing
Precipitating electron energies range from ~0.4 to ~25 keV with a characteristic energy of 3.6 keV, consistent with a low color ratio of the auroral emissions
The instrument background caused by > ~5–10 MeV penetrating electrons increased during the crossing, opposite to what is observed at Io
One of the most intriguing discoveries of Juno is the quasi-systematic detection of upgoing electrons above the auroral regions. Here we discuss a by-product of the most energetic component of this ...population: a contamination resembling bar codes in the Juno-UVS images. This pattern is likely caused by bursts of ∼10 MeV electrons penetrating the instrument. These events are mostly detected when Juno’s magnetic footprint is located poleward of the main emission relative to the magnetic pole. The signal is not periodic, but the bursts are typically 0.1–1 s apart. They are essentially detected when Juno-UVS is oriented toward Jupiter, indicating that the signal is due to upgoing electrons. The event detections occur between 1 and 7 Jovian radii above the 1-bar level, suggesting that the electron acceleration takes place close to Jupiter and is thus both strong and brief.
Aims. Following the announcement of the detection of phosphine (PH3) in the cloud deck of Venus at millimeter wavelengths, we have searched for other possible signatures of this molecule in the ...infrared range.Methods. Since 2012, we have been observing Venus in the thermal infrared at various wavelengths to monitor the behavior of SO2 and H2O at the cloud top. We have identified a spectral interval recorded in March 2015 around 950 cm−1 where a PH3 transition is present.Results. From the absence of any feature at this frequency, we derive, on the disk-integrated spectrum, a 3-σ upper limit of 5 ppbv for the PH3 mixing ratio, assumed to be constant throughout the atmosphere. This limit is 4 times lower than the disk-integrated mixing ratio derived at millimeter wavelengths.Conclusions. Our result brings a strong constraint on the maximum PH3 abundance at the cloud top and in the lower mesosphere of Venus.
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