Hercules A

Hercules A
Radio-Optical View of the Galaxy Hercules A - Many thanks to: NASA, ESA, S. Baum and C. O'Dea (RIT), R. Perley and W. Cotton (NRAO/AUI/NSF), and the Hubble Heritage Team (STScI/AURA)

Monday, December 11, 2017

Links to abstracts for 9 Juno related papers at AGU 2017 Fall Meeting

Links to abstracts for 9 Juno related papers at AGU 2017 Fall Meeting

U21A-01: A comparative examination of auroral acceleration processes at Jupiter and Earth as enabled by the Juno mission to Jupiter

"Particle distributions observed by Juno’s Energetic Particle Detector Investigation (JEDI) at low altitudes over Jupiter’s polar regions are exceedingly diverse in directionality and in the shapes of their 3-dimensional energy distributions. Asymmetric, bi-directional angular beams with broad energy distributions are often observed near Jupiter’s main auroral oval with considerable variability as to whether upward or downward intensities are the strongest. Signatures of upward and downward magnetic field-aligned potentials, with inferred potentials up to 100’s of kV are sometimes observed, but unlike at Earth, these potentials do not seem to be associated with the strongest discrete-like auroral emission intensities. Particle distributions have similarities to those observed at Earth over the various phenomenological auroral emission regions, but they are observed in unexpected places with respect to the strongest auroral emission regions, and the jovian distributions are much more energetic. We present a comparative examination of auroral acceleration processes observed at Earth and Jupiter in relation to the respective auroral emission regions."


U21A-02: An overview of the first year of observations of Jupiter’s auroras by Juno-UVS with multi-wavelength comparisons

"Juno’s Ultraviolet Spectrograph (Juno-UVS) has observed the Jovian aurora during eight perijove passes. UVS typically observes Jupiter for 10 hours centered on closest approach in a series of swaths, with one swath per Juno spin (~30s). During this period the spacecraft range to Jupiter’s aurora decreases from ~6 RJ to ~0.3 RJ (or less) in the north, and then reverses this in the south, so that spatial resolution changes dramatically. A scan mirror is used to target different features or raster across the entire auroral region. Juno-UVS observes a particular location for roughly 17 ms/swath, so the series of swaths provide snapshots of ultraviolet auroral brightness and color. A variety of forms and activity levels are represented in the Juno-UVS data–some have been described before with HST observations, but others are new. One interesting result is that the color ratio, often used as a proxy for energetic particle precipitation, may instead (in certain regions) indicate excitation of H2 by low-energy ionospheric electrons. Additional results from comparisons with simultaneous observations at x-ray, visible, and near-IR wavelengths will also be presented."


U21A-03: The Jupiter gravity field from the first year of Juno science operations

"Through November 2017 the Juno spacecraft has completed nine science orbits about Jupiter. Five of the nine perijove passes, when the spacecraft was closest to Jupiter, were arranged to provide accurate measurements of the Doppler shift of the Juno radio signal in order to determine the Jupiter gravity field. The estimated gravity field has been used to place constraints on the interior structure of Jupiter and and effects caused by differential rotation. The Doppler measurements are also used to estimate the response of Jupiter to tides raised by the Galilean satellites, and the Jupiter rotation axis direction and precession rate. We report on the current status of the gravity estimates and the expected results from the rest of the mission duration."


U21A-04: Jupiter’s Magnetic Field and Magnetosphere after Juno’s First 8 Orbits 

"The Juno spacecraft entered polar orbit about Jupiter on July 4, 2016, embarking upon an ambitious mission to map Jupiter’s magnetic and gravitational potential fields and probe its deep atmosphere, in search of clues to the planet’s formation and evolution. Juno is also instrumented to conduct the first exploration of the polar magnetosphere and to acquire images and spectra of its polar auroras and atmosphere. Juno’s 53.5-day orbit trajectory carries her science instruments from pole to pole in approximately 2 hours, with a closest approach to within ~1.05 Rj of the center of the planet (one Rj = 71,492 km, Jupiter’s equatorial radius), just a few thousand km above the clouds. Repeated periapsis passes will eventually encircle the planet with a dense net of observations equally spaced in longitude (<12° at the equator) and optimized for characterization of the Jovian dynamo. Such close passages are sensitive to small spatial scale variations in the magnetic field and therefore many such passes are required to bring the magnetic field into focus. Nevertheless, after only 8 orbits, low-degree spherical harmonics can be extracted from a partial solution to a much more complicated representation (e.g., 20 degree/order), providing the first new information about Jupiter’s magnetic field in decades. Juno is equipped with two magnetometer sensor suites, located 10 and 12 m from the center of the spacecraft at the end of one of Juno’s three solar panel wings. Each contains a vector fluxgate magnetometer (FGM) sensor and a pair of co-located non-magnetic star tracker camera heads, providing accurate attitude determination for the FGM sensors. We present an overview of the magnetometer observations obtained during Juno’s first year in orbit in context with prior observations and those acquired by Juno’s other science instruments."


U21A-05: Results on Jupiter’s Atmosphere from the Juno Microwave Radiometer

"The Juno Microwave Radiometer (MWR) was designed to investigate Jupiter’s atmosphere and radiation belts as one of a suite of instruments on the Juno mission. The MWR’s main objective is to investigate the composition and dynamics of Jupiter’s neutral atmosphere. Juno has now completed eight perijove passes that sample the atmosphere approximately every 45° in longitude, and the MWR has completed its main collection of data pertaining to the composition and structure of Jupiter’s atmosphere. The primary results for atmospheric structure elaborate on the original discovery that the concentration of ammonia is far from uniformly mixed beneath its saturation level in the atmosphere and that deep atmospheric circulations control its distribution. Conversely, features of the deep circulation may be inferred from this distribution. Distinct circulation patterns are seen for three latitudinal regions: 1) Equatorial, where a column of increased ammonia concentration associated with the equatorial zone is sandwiched by off-equatorial regions of depleted ammonia in the north and south equatorial belts, with structure apparent to approximately the 100-bar pressure level, 2) Midlatitudes, where a stratified ammonia concentration appears stable, and 3) Polar, dominated by deep vertical structures associated with the observed surface vortices. Longitudinal structure is seen in the equatorial region primarily above the level of the water cloud around the 8-bar level, while significant structure appears small or absent outside and below this region. The ability of the MWR to detect lightning at its longest wavelengths was unexpected but sheds light on the presence of water and the distribution of strong convective regions in the atmosphere. The implications of these results for atmospheric dynamics and composition will be discussed."


U21A-06: One-Year Observations of Jupiter by the Jovian Infrared Auroral Mapper on Juno

"The Jovian InfraRed Auroral Mapper (JIRAM) [1] on board the Juno [2,3] spacecraft, is equipped with an infrared camera and a spectrometer working in the spectral range 2-5 μm. JIRAM was built to study the infrared aurora of Jupiter as well as to map the planet’s atmosphere in the 5 µm spectral region. The spectroscopic observations are used for studying clouds and measuring the abundance of some chemical species that have importance in the atmosphere’s chemistry, microphysics and dynamics like water, ammonia and phosphine.
During 2017 the instrument will operate during all 7 of Juno’s Jupiter flybys. JIRAM has performed several observations of the polar regions of the planet addressing the aurora and the atmosphere. Unprecedented views of the aurora and the polar atmospheric structures have been obtained. We present a survey of the most significant observations that the instrument has performed during the current year.
[1] Adriani A. et al., JIRAM, the Jovian Infrared Auroral Mapper. Space Sci. Rew., DOI: 10.1007/s11214-014-0094-y, 2014.
[2] Bolton S.J. et al., Jupiter’s interior and deep atmosphere: The initial pole-to-pole passes with the Juno spacecraft. Science DOI: 10.1126/science.aal2108, 2017.
[3] Connerney J. E.P. et al., Jupiter’s magnetosphere and aurorae observed by the Juno spacecraft during its first polar orbits. Science, DOI: 10.1126/science.aam5928, 2017."


U21A-07: Observations by the Juno Waves Investigation at Jupiter

"The Juno spacecraft successfully entered into a highly elliptic polar orbit of Jupiter in July 2016, providing a unique opportunity to explore the Jovian polar magnetosphere and the region between the rings and atmosphere. Juno’s science payload employs a suite of particle, field, and remote sensing instruments to characterize the Jovian magnetosphere and provide remote observations of Jupiter’s auroras. The radio and plasma wave instrument (“Waves”) measures one electric field component of waves in the frequency range of 50 Hz to 40 MHz and one magnetic field component of waves in the range of 50 Hz to 20 kHz. The initial orbits have revealed a number of radio and plasma wave phenomena related to auroral processes, including auroral hiss, electron phase space holes, and a number of encounters or near encounters with the auroral radio emission source regions. The Waves instrument also observes both electron and proton whistlers from lightning, and detects impulses due to impacts of micron-sized grains near Jupiter’s equator. In the outer magnetosphere, trapped continuum radiation is observed, and numerous magnetopause and bow shock crossings have been encountered. In this talk we provide an overview of these and other early results from the Juno Waves investigation."
https://doi.org/10.1002/2017GL072889,   https://doi.org/10.1002/2017GL072850,   https://doi.org/10.1002/2017GL073073


U21A-08: The first year of observations of Jupiter’s magnetosphere from Juno's Jovian Auroral Distributions Experiment (JADE)

"Juno observations of the Jovian plasma environment are made by the Jovian Auroral Distributions Experiment (JADE) which consists of two nearly identical electron sensors – JADE-E – and an ion sensor – JADE-I. JADE-E measures the electron distribution in the range of 100 eV to 100 keV and uses electrostatic deflection to measure the full pitch angle distribution. JADE-I measures the composition separated energy per charge in the range of 10 eV / q to 46 keV / q. The large orbit – apojove ~ 110 Rj, perijove ~1.05 Rj – allows JADE to periodically cross through the magnetopause into the magnetosheath, transverse the outer, middle, and inner magnetosphere, and measures the plasma population down to the ionosphere. We present here in situ plasma observations of the Jovian magnetosphere and topside ionosphere made by the JADE instrument during the first year in orbit.
Dawn-side crossings of the plasmapause have shown a general dearth of heavy ions except during some intervals at lower magnetic latitudes. Plasma disk crossings in the middle and inner magnetosphere show a mixture of heavy and light ions. During perijove crossings at high latitudes when Juno was connected to the Io torus, JADE-I observed heavy ions with energies consistent with a corotating pickup population. In the auroral regions the core of the electron energy distribution is generally from about 100 eV when on field lines that are connected to the inner plasmasheet, several keVs when connected to the outer plasmasheet, and tens of keVs when Juno is over the polar regions. JADE has observed upward electron beams and upward loss cones, both in the north and south auroral regions, and downward electron beams in the south. Some of the beams are of short duration (~ 1 s) implying that the magnetosphere has a very fine spatial and/or temporal structure within the auroral regions. Joint observations with the Waves instrument have demonstrated that the observed loss cone distributions provide sufficient growth rates to drive the cyclotron maser instability. The high velocity of the Juno spacecraft near perijove (~50 km/s) allows observations for of very low energy ions in the spacecraft ram direction, down to below 1 eV/q for protons."


U21A-09: JunoCam Images of Jupiter: Science from an Outreach Experiment

The Juno mission to Jupiter carries a visible imager on its payload primarily for outreach, and also very useful for jovian atmospheric science. Lacking a formal imaging science team, members of the public have volunteered to process JunoCam images. Lightly processed and raw JunoCam data are posted on the JunoCam webpage at https://missionjuno.swri.edu/junocam/processing. Citizen scientists download these images and upload their processed contributions.
JunoCam images through broadband red, green and blue filters and a narrowband methane filter centered at 889 nm mounted directly on the detector. JunoCam is a push-frame imager with a 58 deg wide field of view covering a 1600 pixel width, and builds the second dimension of the image as the spacecraft rotates. This design enables capture of the entire pole of Jupiter in a single image at low emission angle when Juno is ~1 hour from perijove (closest approach). At perijove the wide field of view images are high-resolution while still capturing entire storms, e.g. the Great Red Spot.
Juno’s unique polar orbit yields polar perspectives unavailable to earth-based observers or most previous spacecraft. The first discovery was that the familiar belt-zone structure gives way to more chaotic storms, with cyclones grouped around both the north and south poles [1, 2]. Recent time-lapse sequences have enabled measurement of the rotation rates and wind speeds of these circumpolar cyclones [3].
Other topics are being investigated with substantial, in many cases essential, contributions from citizen scientists. These include correlating the high resolution JunoCam images to storms and disruptions of the belts and zones tracked throughout the historical record. A phase function for Jupiter is being developed empirically to allow image brightness to be flattened from the subsolar point to the terminator. We are studying high hazes and the stratigraphy of the upper atmosphere, utilizing the methane filter, structures illuminated beyond the terminator, and clouds casting shadows. Numerous high altitude clouds have been detected and we are investigating whether they are the jovian equivalent of squall lines."

[1] Bolton, S. et al. (2017) Science 356:821; [2] Orton, G. et al. (2017) GRL 44:4599; [3] Adriani, A. et al. (2017) submitted to Nature.




Introductory Radio Astronomy links:
Magnetosphere of Jupiter :
Jupiter events at Juno Waves and other observatories :
Jupiter events at the University of Iowa Space Physics LWA1 Data Project :
Examples of Jupiter events observed by Juno Waves :