Explanation of dominant oblique radio emission at Jupiter and comparison to the terrestrial case

International audienceThe Io-Jupiter S-bursts are series of quasi-periodic impulsive decameter radio emissions from the magnetic flux tube connecting Jupiter to its closest galilean satellite Io. This paper discusses the possibility, suggested by previous works by Hess et al., that the S-bursts are triggered by upgoing electrons accelerated (downward) by trapped Alfvén waves, that have mirrored above the Jupiter ionosphere. According to this theory, the S-bursts would correspond to wave modes that propagate at oblique angles with respect to the magnetic field. Oblique propagation is also inferred for the more slowly varying components of Io-Jupiter radio emissions. Previous works, mainly based on observations of the terrestrial AKR, whose generation process is closely related to those of S-bursts, showed that these waves are emitted on perpendicular wave modes. This discrepancy between the Jovian and Terrestrial cases has led to a controversy about the credibility of the S-bursts model by Hess et al. In the present paper, we show that indeed, the most unstable wave modes for Earth AKR, and Io-Jupiter S-bursts, as they are seen from ground based radio-telescopes, are not the same. Several causes are evaluated: observational bias, the different degree of plasma magnetization above Earth and Jupiter, the role of a cold plasma component and of plasma auroral cavities. Furthermore, we make predictions about what kind of radiation modes a probe crossing the low altitude Io-Jupiter flux tube will see

Un astronome et l’astrologie...

En observateur de l’engouement pour l’astrologie d’un grand nombre de Français – dont des figures politiques – Philippe Zarka veut réactualiser et moderniser le discours de l’astronome. Pour combattre des idées reçues trop ancrées dans l’esprit de ses concitoyens

Magnetospheric Radio Emissions from Exoplanets with the SKA

Planetary-scale magnetic fields are a window to a planet’s interior and provide shielding of the planet’s atmosphere and surface for life. The Earth, Mercury, Ganymede, and the giant planets of the solar system all contain internal dynamo currents that generate planetary-scale magnetic fields. When coupled to energetic (keV) electrons, such as those produced by solar wind-magnetosphere interaction (compression or magnetic reconnection), magnetosphere-ionosphere or magnetosphere-satellite coupling, the polar regions of a planetary magnetic field are the place of intense, coherent, circularly polarized cyclotron radio emissions. These emissions – that may be as intense as solar ones – are produced by all magnetized planets in the solar system in the MHz range, and up to 40 MHz at Jupiter. Detection of similar emissions from exoplanets will provide constraints on the thermal state, composition, and dynamics of their interior – very difficult to determine by other means – as well as an improved understanding of the planetary dynamo process and of the physics of star-planet plasma interactions. Detailed knowledge of magnetospheric emissions from solar system planets and the discovery of exoplanets motivated both theoretical and observational work on magnetospheric emissions from exoplanets. Scaling laws and theoretical frameworks were built and extrapolated to obtain order-of-magnitude predictions of frequencies and flux densities of exoplanetary radio emissions. The present stage of the theory suggests that radio detection of exoplanets will develop the new field of comparative exo-magnetospheric physics, but also permit to measure exoplanetary parameters such as rotation or orbit inclination. Observational searches started even before the confirmed discovery of the first exoplanet. We review the scientific return of the detection of exoplanetary radio emissions, the current status of observational searches, and discuss the future promise in the context of SKA, especially SKA1-LOW. To the extent that Jupiter’s magnetic field is not exceptionally strong, the current lower frequency limit of 50 MHz implies that SKA1-LOW will likely detect Jovian-mass planets. With the currently planned sensitivity of SKA1-LOW, we estimate that a Jupiter-like planet could be detected to about 10 pc. Within this volume there are ∼200 known stars and ∼35 currently known exoplanets, and this number should increase substantially with coming space missions dedicated to transits and powerful ground-based instruments. The accessible volume will be much increased if scaling laws derived in our solar system can be reliably extrapolated to exoplanetary systems, permitting to measure lower mass planets’ dynamos and magnetospheres

Refurbishing Voyager 1 & 2 Planetary Radio Astronomy (PRA) Data

Voyager/PRA (Planetary Radio Astronomy) data from digitized tapes archived at CNES have been reprocessed and recalibrated. The data cover the Jupiter and Saturn flybys of both Voyager probes. We have also reconstructed goniopolarimetric datasets (flux and polarization) at full resolution. These datasets are currently not available to the scientific community, but they are of primary interest for the analysis of the Cassini data at Saturn, and the Juno data at Jupiter, as well as for the preparation of the JUICE mission. We present the first results derived from the re-analysis of this dataset.Comment: Accepted manuscript for PRE8 (Planetary Radio Emission VIII conference) proceeding

Magnetospheric Radio Emissions from Exoplanets with the SKA

Planetary-scale magnetic fields are a window to a planet’s interior and provide shielding of the planet’s atmosphere and surface for life. The Earth, Mercury, Ganymede, and the giant planets of the solar system all contain internal dynamo currents that generate planetary-scale magnetic fields. When coupled to energetic (keV) electrons, such as those produced by solar wind-magnetosphere interaction (compression or magnetic reconnection), magnetosphere-ionosphere or magnetosphere-satellite coupling, the polar regions of a planetary magnetic field are the place of intense, coherent, circularly polarized cyclotron radio emissions. These emissions – that may be as intense as solar ones – are produced by all magnetized planets in the solar system in the MHz range, and up to 40 MHz at Jupiter. Detection of similar emissions from exoplanets will provide constraints on the thermal state, composition, and dynamics of their interior – very difficult to determine by other means – as well as an improved understanding of the planetary dynamo process and of the physics of star-planet plasma interactions. Detailed knowledge of magnetospheric emissions from solar system planets and the discovery of exoplanets motivated both theoretical and observational work on magnetospheric emissions from exoplanets. Scaling laws and theoretical frameworks were built and extrapolated to obtain order-of-magnitude predictions of frequencies and flux densities of exoplanetary radio emissions. The present stage of the theory suggests that radio detection of exoplanets will develop the new field of comparative exo-magnetospheric physics, but also permit to measure exoplanetary parameters such as rotation or orbit inclination. Observational searches started even before the confirmed discovery of the first exoplanet. We review the scientific return of the detection of exoplanetary radio emissions, the current status of observational searches, and discuss the future promise in the context of SKA, especially SKA1-LOW. To the extent that Jupiter’s magnetic field is not exceptionally strong, the current lower frequency limit of 50 MHz implies that SKA1-LOW will likely detect Jovian-mass planets. With the currently planned sensitivity of SKA1-LOW, we estimate that a Jupiter-like planet could be detected to about 10 pc. Within this volume there are ∼200 known stars and ∼35 currently known exoplanets, and this number should increase substantially with coming space missions dedicated to transits and powerful ground-based instruments. The accessible volume will be much increased if scaling laws derived in our solar system can be reliably extrapolated to exoplanetary systems, permitting to measure lower mass planets’ dynamos and magnetospheres

Fine structures of radio bursts from flare star AD Leo with FAST observations

Radio bursts from nearby active M-dwarfs have been frequently reported and extensively studied in solar or planetary paradigms. Whereas, their sub-structures or fine structures remain rarely explored despite their potential significance in diagnosing the plasma and magnetic field properties of the star. Such studies in the past have been limited by the sensitivity of radio telescopes. Here we report the inspiring results from the high time-resolution observations of a known flare star AD Leo with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). We detected many radio bursts in the two days of observations with fine structures in the form of numerous millisecond-scale sub-bursts. Sub-bursts on the first day display stripe-like shapes with nearly uniform frequency drift rates, which are possibly stellar analogs to Jovian S-bursts. Sub-bursts on the second day, however, reveal a different blob-like shape with random occurrence patterns and are akin to solar radio spikes. The new observational results suggest that the intense emission from AD Leo is driven by electron cyclotron maser instability which may be related to stellar flares or interactions with a planetary companion.Comment: 25 pages, 12 figures, accepted for publication in Ap

The LOFAR Transients Pipeline

Current and future astronomical survey facilities provide a remarkably rich opportunity for transient astronomy, combining unprecedented fields of view with high sensitivity and the ability to access previously unexplored wavelength regimes. This is particularly true of LOFAR, a recently-commissioned, low-frequency radio interferometer, based in the Netherlands and with stations across Europe. The identification of and response to transients is one of LOFAR's key science goals. However, the large data volumes which LOFAR produces, combined with the scientific requirement for rapid response, make automation essential. To support this, we have developed the LOFAR Transients Pipeline, or TraP. The TraP ingests multi-frequency image data from LOFAR or other instruments and searches it for transients and variables, providing automatic alerts of significant detections and populating a lightcurve database for further analysis by astronomers. Here, we discuss the scientific goals of the TraP and how it has been designed to meet them. We describe its implementation, including both the algorithms adopted to maximize performance as well as the development methodology used to ensure it is robust and reliable, particularly in the presence of artefacts typical of radio astronomy imaging. Finally, we report on a series of tests of the pipeline carried out using simulated LOFAR observations with a known population of transients.Comment: 30 pages, 11 figures; Accepted for publication in Astronomy & Computing; Code at https://github.com/transientskp/tk