Abstract
AbstractThe jovian moon Io disperses about 1 ton/s of material in the planetary magnetosphere, mainly by sublimation of SO2 from the surface and by its intense volcanic activity. The ejected material supplies the plasma cloud surrounding Jupiter known as Io Plasma Torus (IPT). The radio communication between Juno and the Earth DSN station crosses the IPT near the closest approach. Being a dispersive medium, the IPT introduces a path delay in the signal, which can be analyzed to retrieve the density distribution of electrons. We used radio tracking data from the first 25 orbits to investigate the morphology of the IPT and its variability. We adopted a static and axisymmetric model for the electron density and we updated it including temporal and longitudinal variability. We found that our best fit model must include both variabilities, even though on average the morphology of the IPT agrees with previous analyses. Our results suggest that the density of the outer region of the IPT fluctuates over 50% the average value over a typical time scale of about 420 days.
Highlights
Ten years after the discovery of the magnetosphere of Jupiter, Bigg (1964) pointed out that the modulation in the observed radio emission bursts was related to the phase of Io, the innermost Galilean moon, and so he laid the foundations for the study of the interaction between natural satellites and a planetary magnetosphere.In the 70s, ground-based spectroscopic observations revealed the presence of neutral sodium associated with Io (Brown & Chaffee, 1974)
For each occultations we found that the relative difference between the total electron content (TEC) computed with the full 3D geometry and the one obtained with the approximation is usually less than 1% and almost never greater than 5%, except far from the occultation, wEhere TEC 0, making the relative error large even though the absolute TEC difference is small
In order to quantify the difference between the axisymmetric and other models, we reported the difference between the square root of the mean weighted sum of squared residuals (MWSSR) of the axisymmetric model and the MWSSR of the mixed model
Summary
Ten years after the discovery of the magnetosphere of Jupiter, Bigg (1964) pointed out that the modulation in the observed radio emission bursts was related to the phase of Io, the innermost Galilean moon, and so he laid the foundations for the study of the interaction between natural satellites and a planetary magnetosphere.In the 70s, ground-based spectroscopic observations revealed the presence of neutral sodium associated with Io (Brown & Chaffee, 1974). Ten years after the discovery of the magnetosphere of Jupiter, Bigg (1964) pointed out that the modulation in the observed radio emission bursts was related to the phase of Io, the innermost Galilean moon, and so he laid the foundations for the study of the interaction between natural satellites and a planetary magnetosphere. A few years later, Kupo et al (1976) detected a toroidal cloud of singly ionized sulphur around Jupiter inside Io’s orbit using spectrographic plates, which was thought to be originated in an annular cloud of cold plasma in the same region A. Brown, 1976): this is the first detection of the so-called Io Plasma Torus (IPT). In the same decade, Hill et al (1974) theorized the inflation of Jupiter’s magnetic field due to centrifugal stress of nearly corotating plasma and formulated the centrifugal equator, which corresponds to the midplane of the cold torus. Because the magnetic equator of Jupiter is tilted with respect to the rotational equator, the tilt of the centrifugal equator is 2/3 the way from the rotational to the magnetic equator
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