The foreshocks of outer planets

BERTUCCI, C.; ANDRES, N.; GOMEZ, D. O.; MAZELLE, C. X.; ACHILLEOS, N. A.; DOUGHERTY, M. K.

Congreso; AGU Fall Meeting 2012; 2012

The presence of non-absorbing planetary obstacles in the supermagnetosonic solar wind makes foreshocks a rather common element throughout the solar system. Although the observations at Earth represent a vital element in the study of the physical processes occurring on planetary foreshocks at large, these phenomena necessarily occur at the particular parameter values relevant for our planet. In particular, the shocks of the outer planets are characterized by high solar wind Mach numbers, and in the case of the giant planets, by an extremely high size parameter/solar wind ion gyroradius ratio, in contrast to small magnetized planets, or unmagnetized planets such as Mercury and Mars, respectively. In addition, the geometry of their foreshocks present symmetries associated with the evolution of the interplanetary magnetic field direction with heliospheric distance, and waves within a range of frequencies which is unusual for the inner solar system. In this work, we review past and current studies on the foreshocks of outer planets from in situ magnetic field and plasma observations, with emphasis on Jupiter and Saturn. In particular, we will discuss the properties of plasma waves found within their ion foreshocks, the possible mechanisms generating them, and the similarities and differences with foreshock wave phenomena at Earth.