Star-Planet Interactions in the Radio Domain: Prospect for Their Detection

Abstract

All possible types of interaction of a magnetized plasma flow with an obstacle (magnetized or not) are considered, and those susceptible to produce a radio signature are identified. The role of the sub-Alfvénic or super-Alfvénic character of the flow is discussed. Known examples in the solar system are given, as well as extrapolations to starplanet plasma interactions. The dissipated power and the fraction that goes into radio waves are evaluated in the frame of the radio-magnetic scaling law, the theoretical bases and validity of which are discussed in the light of recent works. Then it is shown how radio signatures can be interpreted, in the frame of the cyclotron-maser theory (developed for explaining the generation of solar system planetary auroral and satellite-induced radio emissions), for deducing many physical parameters of the system studied, including the planetary or stellar magnetic field. Prospects for the detection of such radio signatures with new generation low-frequency radiotelescopes are then outlined.

Jupiter radio emission induced by Ganymede and consequences for the radio detection of exoplanets

“…In order to determine which scaling law applies, the paradigm of solar wind-planet interaction was generalized to the interaction between a magnetized flow and a conductive obstacle (magnetized or not), leading to dissipation of the flow's power (kinetic and magnetic) on the obstacle, a fraction of which goes into electron acceleration and precipitation generating radio emissions (Zarka 2017). This paradigm can be applied to satellite-Jupiter interactions.…”

Detecting exoplanets with FAST?

“…The energy drivers for electron acceleration up to keV energies include (Zarka et al 2001;Zarka 2007Zarka , 2017Nichols 2011):…”

“…A frequency >70 MHz corre- sponds to cyclotron emission from a source with a magnetic field amplitude > 25 G. Figure 3 shows the FAST sensitivity (as well as that of other low-frequency instruments) compared to the predicted maximum emission frequency and expected radio flux for known exoplanets in 2011, extrapolated following Grießmeier et al (2007). Only a few candidate exoplanets have a predicted magnetic field reaching or exceeding 25 G. FAST will thus likely be best adapted to search for SPI emissions (exoplanet-induced as proposed by Zarka (2007Zarka ( , 2017, including for terrestrial planets around white dwarfs as proposed by Willes & Wu (2004, 2005), down to moderate intensities, whereas magnetospheric exoplanetary emissions will be rather the target of lower frequency radio arrays such as LOFAR (van Haarlem et al 2013) and NenuFAR (Zarka et al 2012(Zarka et al , 2015b.…”

Radio emission from satellite-Jupiter interactions (especially Ganymede)

“…Signatures of electron acceleration due to the above interactions have been detected in the form of ultraviolet emissions from the magnetic footprints of Io, Ganymede and Europa on Jupiter [Clarke et al, 2002]. A radio-magnetic scaling law has been proposed to quantify the energetics of satellite-planet and solar wind-magnetosphere interactions in a unified frame [Zarka, 2007;2017]. Detecting the radio emissions induced by satellites other than Io in Jupiter's magnetic field (hereafter called simply satellite-induced radio emissions) is essential for better characterizing these interactions and test and constrain the radio-magnetic scaling law, in order to extrapolate it confidently to star-exoplanet interactions.…”