The Integrated Science Investigation of the Sun (ISIS) is a complete science investigation on the Solar Probe Plus (SPP) mission, which flies to within nine solar radii of the Sun’s surface. ISIS ...comprises a two-instrument suite to measure energetic particles over a very broad energy range, as well as coordinated management, science operations, data processing, and scientific analysis. Together, ISIS observations allow us to explore the mechanisms of energetic particles dynamics, including their: (1) Origins—defining the seed populations and physical conditions necessary for energetic particle acceleration; (2) Acceleration—determining the roles of shocks, reconnection, waves, and turbulence in accelerating energetic particles; and (3) Transport—revealing how energetic particles propagate from the corona out into the heliosphere. The two ISIS Energetic Particle Instruments measure lower (EPI-Lo) and higher (EPI-Hi) energy particles. EPI-Lo measures ions and ion composition from ∼20 keV/nucleon–15 MeV total energy and electrons from ∼25–1000 keV. EPI-Hi measures ions from ∼1–200 MeV/nucleon and electrons from ∼0.5–6 MeV. EPI-Lo comprises 80 tiny apertures with fields-of-view (FOVs) that sample over nearly a complete hemisphere, while EPI-Hi combines three telescopes that together provide five large-FOV apertures. ISIS observes continuously inside of 0.25 AU with a high data collection rate and burst data (EPI-Lo) coordinated with the rest of the SPP payload; outside of 0.25 AU, ISIS runs in low-rate science mode whenever feasible to capture as complete a record as possible of the solar energetic particle environment and provide calibration and continuity for measurements closer in to the Sun. The ISIS Science Operations Center plans and executes commanding, receives and analyzes all ISIS data, and coordinates science observations and analyses with the rest of the SPP science investigations. Together, ISIS’ unique observations on SPP will enable the discovery, untangling, and understanding of the important physical processes that govern energetic particles in the innermost regions of our heliosphere, for the first time. This paper summarizes the ISIS investigation at the time of the SPP mission Preliminary Design Review in January 2014.
Jupiter's ultraviolet (UV) aurorae, the most powerful and intense in the solar system, are caused by energetic electrons precipitating from the magnetosphere into the atmosphere where they excite the ...molecular hydrogen. Previous studies focused on case analyses and/or greater than 30‐keV energy electrons. Here for the first time we provide a comprehensive evaluation of Jovian auroral electron characteristics over the entire relevant range of energies (~100 eV to ~1 MeV). The focus is on the first eight perijoves providing a coarse but complete System III view of the northern and southern auroral regions with corresponding UV observations. The latest magnetic field model JRM09 with a current sheet model is used to map Juno's magnetic foot point onto the UV images and relate the electron measurements to the UV features. We find a recurring pattern where the 3‐ to 30‐keV electron energy flux peaks in a region just equatorward of the main emission. The region corresponds to a minimum of the electron characteristic energy (<10 keV). Its polarward edge corresponds to the equatorward edge of the main oval, which is mapped at M shells of ~51. A refined current sheet model will likely bring this boundary closer to the expected 20–30 RJ. Outside that region, the >100‐keV electrons contribute to most (>~70–80%) of the total downward energy flux and the characteristic energy is usually around 100 keV or higher. We examine the UV brightness per incident energy flux as a function of characteristic energy and compare it to expectations from a model.
Plain Language Summary
Aurorae, also commonly called Northern or Southern Lights, are among the most spectacular displays of nature. They are observed not only at Earth but at other planets too, such as Mars, Jupiter, and Saturn. In fact, Jupiter has the brightest aurora in the solar system. The aurora is created when electrons and/or ions in space precipitate into the atmosphere and excite the ambient gas. At Jupiter, they mostly shine in the ultraviolet which is invisible to our eyes but can be seen with suitable instrumentation. The faster the electrons, the deeper they go into the atmosphere, but also the more energy they carry, which eventually can be converted to create more light. This study is about characterizing the electrons that create Jupiter's aurora using many instruments from the National Aeronautics and Space Administration's Juno Mission. We find that different ultraviolet emissions correspond to different electron characteristics. Knowing the differences will help us to understand the bigger picture to explain the processes that create the aurora.
Key Points
We present a survey of Jovian auroral electrons characteristics from 50 eV to 1000 keV by Juno
We present a metric to identify main oval crossings in electron data using 3‐30 keV electrons energy flux
We estimate the UV brightness per incident electron energy flux as a function of characteristic energy
Abstract
We present the first interferometric detections of fast radio bursts (FRBs), an enigmatic new class of astrophysical transient. In a 180-d survey of the Southern sky, we discovered three ...FRBs at 843 MHz with the UTMOST array, as a part of commissioning science during a major ongoing upgrade. The wide field of view of UTMOST (≈9 deg2) is well suited to FRB searches. The primary beam is covered by 352 partially overlapping fan-beams, each of which is searched for FRBs in real time with pulse widths in the range 0.655–42 ms, and dispersion measures ≤2000 pc cm−3. Detections of FRBs with the UTMOST array place a lower limit on their distances of ≈104 km (limit of the telescope near-field) supporting the case for an astronomical origin. Repeating FRBs at UTMOST or an FRB detected simultaneously with the Parkes radio telescope and UTMOST would allow a few arcsec localization, thereby providing an excellent means of identifying FRB host galaxies, if present. Up to 100 h of followup for each FRB has been carried out with the UTMOST, with no repeating bursts seen. From the detected position, we present 3σ error ellipses of 15 arcsec × 8
${^{\circ}_{.}}$
4 on the sky for the point of origin for the FRBs. We estimate an all-sky FRB rate at 843 MHz above a fluence
$\cal F_\mathrm{lim}$
of 11 Jy ms of ∼78 events sky−1 d−1 at the 95 per cent confidence level. The measured rate of FRBs at 843 MHz is two times higher than we had expected, scaling from the FRB rate at the Parkes radio telescope, assuming that FRBs have a flat spectral index and a uniform distribution in Euclidean space. We examine how this can be explained by FRBs having a steeper spectral index and/or a flatter logN–log
$\mathcal {F}$
distribution than expected for a Euclidean Universe.
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
Using Juno plasma, electric and magnetic field observations (from JADE, Waves, and MAG instruments), we show that electron conic distributions are commonly observed in Jovian radio sources. The ...conics are characterized by maximum fluxes at oblique pitch angles, ~20°–30° from the B field, both in the upward and downward directions. They constitute an efficient source of free energy for the cyclotron maser instability. Growth rates of ~3 to 7 × 104 s−1 are obtained for hectometric waves, leading to amplification by e10 with propagation paths of 50–100 km. We show that stochastic acceleration due to interactions with a low‐frequency electric field turbulence located a few 104 km above the ionosphere may form the observed conics. A possible source of turbulence could be inertial Alfvén waves, suggesting a connection between the auroral acceleration and generation of coherent radio emissions.
Plain Language Summary
Jupiter, as many astrophysical magnetized objects, is a powerful emitter of nonthermal radio emissions. The coherent process required for their generation is likely the cyclotron maser instability (CMI). However, the exact conditions of wave amplification are not known precisely at Jupiter. With Juno mission, for the first time, it is possible to explore the auroral regions of Jupiter, where the particles are accelerated and the nonthermal emissions produced. With several crossing of the radio sources, the free energy used by the CMI can now be identified. It corresponds to conic‐like distributions, characterized by an accumulation of particles just outside the loss cones. Applying the CMI theory, large growth rates are obtained, showing that the conics probably play a central role in the wave generation source. The formation of the conics could be due to an interaction with a low‐frequency Alfvénic turbulence. This suggests a close relationship between the radio wave generation and the particle acceleration, as at Earth, the details of the scenario being, nevertheless, slightly different.
Key Points
Electron conics are observed by Juno in Jovian radio sources, and their role in the wave amplification is analyzed
The observed conics may very efficiently drive the cyclotron maser, from decametric to kilometric wavelength ranges
The formation of conics is modeled by a stochastic acceleration due to a low‐frequency parallel electric field turbulence
Using Juno plasma and wave and magnetic observations (JADE and Waves and MAG instruments), the generation mechanism of the Jovian hectometric radio emission is analyzed. It is shown that suitable ...conditions for the cyclotron maser instability (CMI) are observed in the regions of the radio sources. Pronounced loss cone in the electron distributions are likely the source of free energy for the instability. The theory reveals that sufficient growth rates are obtained from the distribution functions that are measured by the JADE‐Electron instrument. The CMI would be driven by upgoing electron populations at 5–10 keV and 10–30° pitch angle, the amplified waves propagating at 82°–87° from the B field, a fraction of a percent above the gyrofrequency. Typical e‐folding times of 10−4 s are obtained, leading to an amplification path of ~1000 km. Overall, this scenario for generation of the Jovian hectometric waves differs significantly from the case of the auroral kilometric radiation at Earth.
Key Points
First detailed wave/particle investigation in a Jovian radio source, using JADE, Waves, and MAG Juno instruments
Confirmation that the cyclotron maser instability is the generation mechanism
Demonstration that the observed loss cone distributions provide sufficient growth rates to explain the wave amplification
Integrating simultaneous in situ measurements of magnetic field fluctuations, precipitating electrons, and ultraviolet auroral emissions, we find that Alfvénic acceleration mechanisms are responsible ...for Ganymede's auroral footprint tail. Magnetic field perturbations exhibit enhanced Alfvénic activity with Poynting fluxes of ~100 mW/m2. These perturbations are capable of accelerating the observed broadband electrons with precipitating fluxes of ~11 mW/m2, such that Alfvénic power is transferred to electron acceleration with ~10% efficiency. The ultraviolet emissions are consistent with in situ electron measurements, indicating 13 ± 3 mW/m2 of precipitating electron flux. Juno crosses flux tubes with both upward and downward currents connected to the auroral tail exhibiting small‐scale structure. We identify an upward electron conic in the downward current region, possibly due to acceleration by inertial Alfvén waves near the Jovian ionosphere. In concert with in situ observations at Io's footprint tail, these results suggest that Alfvénic acceleration processes are broadly applicable to magnetosphere‐satellite interactions.
Plain Language Summary
Jupiter's moon Ganymede interacts with the planet's rapidly rotating magnetic field, which generates an aurora in the Jovian upper atmosphere. The Juno spacecraft crossed magnetic field lines connected to this aurora. We found that a specific type of wave, similar to a wave produced when a string is plucked, is responsible for accelerating the electrons sustaining this aurora. This type of interaction between a moon and the planet it orbits is likely a common process occurring at other exoplanetary systems.
Key Points
First in situ particles and fields measurements connected to Ganymede's auroral tail are reported
Alfvén wave activity is observed with Poynting fluxes of ~100 mW/m2 capable of accelerating electrons into the atmosphere
Ganymede's footprint tail contains electron populations consistent with Alfvénic acceleration and precipitating energy fluxes of ~11 mW/m2
Jupiter’s interior and deep atmosphere Bolton, S. J.; Adriani, A.; Adumitroaie, V. ...
Science (American Association for the Advancement of Science),
05/2017, Letnik:
356, Številka:
6340
Journal Article
Recenzirano
Odprti dostop
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.
This study presents a survey of ion flow speed, density, temperature, and composition observed by the Jovian Auroral Distributions Experiment Ion (JADE‐I) sensor on Juno from 10–40 RJ in the dawn to ...midnight sector of Jupiter's magnetosphere. The survey covers Juno orbits 5–22, and the observations are separated by equatorial (|zmagRJ| ≤ 1.5) and off‐equator (|zmagRJ|>1.5) regions. Plasma parameters for H+, O+, O2+, O3+, Na+, S+, S2+, and S3+ are derived by forward modeling JADE‐I's energy‐per‐charge versus time‐of‐flight spectra using omnidirectional averaged convected kappa distributions and modeled instrument responses. O+ and S2+ are resolved via a ray‐tracing simulation based on carbon‐foil‐effects. The ion flow speed increases with radial distance and is comparable to rigid corotation speed out to ∼20 RJ. Ion number densities decrease with radial distance, the primary species being H+, O+, and S2+. The relative contribution of H+ and S2+ increases and decreases, respectively, in the off‐equator regions, supporting the interpretation that the latitudinal distribution of ions is mass dependent. The O+ to S2+ and ΣOn+ to ΣSn+ number density ratios are variable, the 5 RJ bin averages for O+ to S2+ ranging from ∼0.75–1.5 (equator) and ∼1.1–1.8 (off‐equator) and ΣOn+ to ΣSn+ from ∼0.6–0.9 (equator) and ∼0.8–1.1 (off‐equator). Both proton and heavy ion temperatures show order of magnitude increases between 10 and 20 RJ and range from ∼100 eV to 10 keV and 1 keV to a few tens of keV, respectively.
Plain Language Summary
The Jovian Auroral Distributions Experiment (JADE) on Juno has continuously investigated the plasma environment in Jupiter's magnetosphere since its arrival in August 2016. The polar‐orbiting spacecraft enables JADE to explore both equatorial and off‐equator regions of Jupiter's plasma sheet. In this study, we present plasma sheet ion characteristics such as ion composition, flow speed, and temperatures for H+, O+, O2+, O3+, Na+, S+, S2+, and S3+ that are originating from the innermost Galilean satellite Io. A spatial dependence of ion characteristics is discussed and compared to previous observations. While the density profiles agree well with the Voyager‐based studies, temperatures found in this study show at least an order of magnitude higher values. A new addition to this paper is that the latitudinal distribution of ions shows trend in the mass. Relative composition of protons increases compared to the heavier ions in the off‐equator regions. These observations provide insights on how the ions are distributed throughout Jupiter's magnetosphere and improve our current understanding on ion dynamics in the plasma sheet.
Key Points
Ion flow speed, number density, temperature, and composition in Jupiter's plasma sheet show radial and/or latitudinal trends
H+, O+, and S2+ are the primary ions, the contribution of H+ and S2+ increasing and decreasing, respectively, in the off‐equator region
The O+ to S2+ density ratio is variable, the 5 RJ bin averages ranging from 0.7–1.5 (equator) and 1.1–1.8 (off‐equator)
Oceanic production of calcium carbonate is conventionally attributed to marine plankton (coccolithophores and foraminifera). Here we report that marine fish produce precipitated carbonates within ...their intestines and excrete these at high rates. When combined with estimates of global fish biomass, this suggests that marine fish contribute 3 to 15% of total oceanic carbonate production. Fish carbonates have a higher magnesium content and solubility than traditional sources, yielding faster dissolution with depth. This may explain up to a quarter of the increase in titratable alkalinity within 1000 meters of the ocean surface, a controversial phenomenon that has puzzled oceanographers for decades. We also predict that fish carbonate production may rise in response to future environmental changes in carbon dioxide, and thus become an increasingly important component of the inorganic carbon cycle.
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