Interaction with interplanetary medium
Immersed in the plasma of the interplanetary medium, a comet may be associated with:
Electrostatic charging of the comet nucleus,[3] and, charging of the dust,[4] resulting in levitation of dust from the comet surface,[4]
Coagulation of grains with opposite potentials,[5] and the opposite process, disruption (break-up) of grains with high potentials,[4]
Plasma instabilities in the tail,[4]
Folding of the interplanetary magnetic field into the tail of the comet (Alfvén's "folding umbrella" hydromagnetic model, 1957)[6] [7]
A cometary current system including plasma tail streamers separated by a neutral current sheet, with a total current exceeding 108A,[7]
A shock-ionopause current system, a tail current system, and a field-aligned auroral current system,[2]
The flow of such field-aligned currents leading to the generation of strong localized field-aligned electric fields (double layers),[2] [8]
Acceleration of electrons to keV energies in such double layers would lead to the observed enhanced fluxes of suprathermal electrons.[2]
Production of X-rays (e.g. such as those detected from Comet Hyakutake,[9][10][11] confirming the presence of Birkeland currents (field-align currents),[12]
Jets, such as those produced and modelled by Kristian Birkeland's theory,[13]
The generation of magnetic fields and electric currents in cometary plasma tails, up to a billion Amps, [14] first proposed by Alfvén in 1957,[6] and "strikingly established during the crossing of the plasma tail of Comet Giacobini—Zinner by the ICE spacecraft on September 11, 1985 (Smith et al., 1986)"[15] [7]
Currents in the cometary atmosphere,[16]
Outbursts from the comet nucleus resulting form macroscopic electric double layers,[17]
The origin of comet striae (banding) in dust tails,[18]
Inner coma cometary plasma formation by the critical ionization velocity mechanism,[19] [20]
Filamentary structure in comet tails interpreted as evidence of field-aligned currents (Birkeland currents),[7]
A "cometary aurora" due to "current discharges into the atmosphere from the tail"[21]
Possible ionization of the inner coma due to cross-tail currents closing through the cometary head.[22]
In 2004, NASA's Stardust spacecraft on a mission to comet Wild 2 (pronounced "Vilt 2"), "found 20 jets, on both the sunlit side of the comet and, surprisingly, the dark side"
