Radio emissions from Jupiter provided the first evidence that this giant planet has a strong magnetic field and a large magnetosphere. Jupiter also has polar aurorae, which are similar in many respects to Earth's aurorae. The radio emissions are believed to be generated along the high-latitude magnetic field lines by the same electrons that produce the aurorae, and both the radio emission in the hectometric frequency range and the aurorae vary considerably. The origin of the variability, however, has been poorly understood. Here we report simultaneous observations using the Cassini and Galileo spacecraft of hectometric radio emissions and extreme ultraviolet auroral emissions from Jupiter. Our results show that both of these emissions are triggered by interplanetary shocks propagating outward from the Sun. When such a shock arrives at Jupiter, it seems to cause a major compression and reconfiguration of the magnetosphere, which produces strong electric fields and therefore electron acceleration along the auroral field lines, similar to the processes that occur during geomagnetic storms at the Earth.

/pdf/control-of-jupiter-s-radio-emission-and-aurorae-by-the-solar-44wc7f82sj.pdf

Control of Jupiter's radio emission and aurorae by the solar wind

Knowledge of the beam profiles is of critical importance for interpreting data from cosmic microwave background experiments. In this paper, we present the characterization of the in-flight optical response of the WMAP satellite. The main-beam intensities have been mapped to ≤-30 dB of their peak values by observing Jupiter with the satellite in the same observing mode as for CMB observations. The beam patterns closely follow the prelaunch expectations. The full width at half-maximum is a function of frequency and ranges from 082 at 23 GHz to 021 at 94 GHz; however, the beams are not Gaussian. We present (a) the beam patterns for all 10 differential radiometers, showing that the patterns are substantially independent of polarization in all but the 23 GHz channel; (b) the effective symmetrized beam patterns that result from WMAP's compound spin observing pattern; (c) the effective window functions for all radiometers and the formalism for propagating the window function uncertainty; and (d) the conversion factor from point-source flux to antenna temperature. A summary of the systematic uncertainties, which currently dominate our knowledge of the beams, is also presented. The constancy of Jupiter's temperature within a frequency band is an essential check of the optical system. The tests enable us to report a calibration of Jupiter to 1%-3% accuracy relative to the CMB dipole.

/pdf/first-year-wilkinson-microwave-anisotropy-probe-wmap-xm29e40a9y.pdf

First-year Wilkinson microwave anisotropy probe (WMAP) observations: Beam profiles and window functions

Knowledge of the beam profiles is of critical importance for interpreting data from cosmic microwave background experiments. In this paper, we present the characterization of the in-flight optical response of the WMAP satellite. The main beam intensities have been mapped to < -30 dB of their peak values by observing Jupiter with the satellite in the same observing mode as for CMB observations. The beam patterns closely follow the pre-launch expectations. The full width at half maximum is a function of frequency and ranges from 0.82 degrees at 23 GHz to 0.21 degrees at 94 GHz; however, the beams are not Gaussian. We present: (a) the beam patterns for all ten differential radiometers and show that the patterns are substantially independent of polarization in all but the 23 GHz channel; (b) the effective symmetrized beam patterns that result from WMAP's compound spin observing pattern; (c) the effective window functions for all radiometers and the formalism for propagating the window function uncertainty; and (d) the conversion factor from point source flux to antenna temperature. A summary of the systematic uncertainties, which currently dominate our knowledge of the beams, is also presented. The constancy of Jupiter's temperature within a frequency band is an essential check of the optical system. The tests enable us to report a calibration of Jupiter to 1-3% accuracy relative to the CMB dipole.

/pdf/first-year-wilkinson-microwave-anisotropy-probe-wmap-2qw3rj81bb.pdf

First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Beam Profiles and Window Functions

Titan's surface at 2.2-cm wavelength imaged by the Cassini RADAR radiometer: Calibration and first results

A comprehensive survey of data from the Galileo spacecraft suggests that the principle mechanism of ultra-relativistic electron acceleration in Jupiter’s magnetosphere arises from their gyro-resonant interaction with whistler waves, in contrast with conventional understanding.

/pdf/gyro-resonant-electron-acceleration-at-jupiter-4vs2y6a5yi.pdf

Gyro-resonant electron acceleration at Jupiter

Ground-based observations have shown that Jupiter is a two-component source of microwave radio emission1: thermal atmospheric emission and synchrotron emission2 from energetic electrons spiralling in Jupiter's magnetic field. Later in situ measurements3,4 confirmed the existence of Jupiter's high-energy electron-radiation belts, with evidence for electrons at energies up to 20 MeV. Although most radiation belt models predict electrons at higher energies5,6, adiabatic diffusion theory can account only for energies up to around 20 MeV. Unambiguous evidence for more energetic electrons is lacking. Here we report observations of 13.8 GHz synchrotron emission that confirm the presence of electrons with energies up to 50 MeV; the data were collected during the Cassini fly-by of Jupiter. These energetic electrons may be repeatedly accelerated through an interaction with plasma waves, which can transfer energy into the electrons. Preliminary comparison of our data with model results suggests that electrons with energies of less than 20 MeV are more numerous than previously believed.

/pdf/ultra-relativistic-electrons-in-jupiter-s-radiation-belts-49gg0wzok9.pdf

T. Bastian

Papers

Ultra-relativistic electrons in Jupiter's radiation belts