Abstract Measurements of >82 MeV Galactic cosmic-ray (GCR) protons at Earth indicate that they may be mixed with protons that leak into the heliosphere from Jupiter’s magnetosphere (Jovian cosmic-ray protons (JCRPs)). A ∼400 day periodicity in these proton fluxes, which is similar to the synodic period between Jupiter and Earth, and an excess proton flux observed when Jupiter and Earth can be connected through the interplanetary magnetic field were the basis for this claim. Using nearly 13 yr of GCR measurements at Saturn with Cassini ’s Magnetosphere Imaging Instrument, we show that the ∼400 day periodicity is also present in ≳100 MeV protons at ∼9.6 au, although the synodic period between Saturn and Jupiter is ∼20 yr. We also find that the features responsible for this periodicity were convected from 1 au to Saturn’s distance with the solar wind velocity. Their origin is therefore heliospheric, not Jovian. We attribute these features to quasi-biennial oscillations, observed in the solar magnetic field and various heliospheric indices. This finding indicates that fluxes of JCRPs at 1 au, if present, are considerably overestimated, because the signal originally attributed to them represents the amplitude of the ∼400 day periodic GCR oscillation. This oscillation has to be subtracted before the resulting proton GCR flux residuals are analyzed in the context of a possible Jovian source. A confirmation of the presence of JCRPs over extended regions in the heliosphere and a constraint on their fractional abundance in GCR spectra may therefore require further validation and analysis, and several options are proposed for this purpose.
Abstract The spatial distribution of whistler‐mode wave emissions in the Jovian magnetosphere measured during the first 45 perijove orbits of Juno is investigated. A double‐belt structure in whistler‐mode wave intensity is revealed. Between the two whistler‐mode belts, there exists a region devoid of 100 s keV electrons near the magnetic equator at . Insufficient source electron population in such an electron “slot” region is a possible explanation for the relatively lower wave activity compared to the whistler‐mode belts. The wave intensity of the outer whistler‐mode belt measured in the dusk‐premidnight sector is significantly stronger than in the postmidnight‐dawn sector. We suggest that the inherent dawn‐dusk asymmetries in source electron distribution and/or auroral hiss emission rather than the modulation of solar cycle are more likely to result in the azimuthal variation of outer whistler‐mode belt intensity during the first 45 Juno perijove orbits.
Abstract Pix.PAN is a compact cylindrical magnetic spectrometer, intended to provide excellent high energy particle measurements under high rate and hostile operating conditions in space. Its principal design is composed of two Halbach-array magnetic sectors and six Timepix4-based tracking layers; the latest hybrid silicon pixel detector readout ASIC designed. Due to Pix.PAN’s compact and relatively simple design, it has the potential to be used for space missions exploring with measurements of unprecedented precision, high energy particles in radiation belts and the heliophere (solar energetic particles, anomalous and galactic cosmic rays). In this white paper, we discuss the design and expected performance of Pix.PAN for COMPASS ( C omprehensive O bservations of M agnetospheric P article A cceleration, S ources, and S inks), a mission concept submitted to NASA’s Call “B.16 Heliophysics Mission Concept Studies (HMCS)” in 2021 that targets the extreme high energy particle environment of Jupiter’s inner radiation belts. We also discuss PixPAN’s operational conditions and interface requirements. The conceptual design shows that is possible to achieve an energy resolution of<12% for electrons in the range of 10 MeV-1 GeV and<35% for protons between $$\sim $$ ∼ 200 MeV to a few GeV. Due to the timestamp precision of Timepix4, a time resolution (on an instrument level) of about 100 ps can be achieved for time-of-flight measurements. In the most intense radiation environments of the COMPASS mission, Pix.PAN is expected to have a maximum hit rate of 44 $$\frac{\text {MHz}}{\text {cm}^2}$$ MHzcm2 which is below the design limit of 360 $$\frac{\text {MHz}}{\text {cm}^2}$$ MHzcm2 of Timepix4. Finally, a sensor design is proposed which allows the instrument to operate with a power budget of 20W without the loss of scientific performance.
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