title: MESSENGER observations of extreme loading and unloading of Mercury's magnetic tail.
abstract: During MESSENGER's third flyby of Mercury, the magnetic field in the planet's magnetic tail increased by factors of 2 to 3.5 over intervals of 2 to 3 minutes. Magnetospheric substorms at Earth are powered by similar tail loading, but the amplitude is lower by a factor of approximately 10 and typical durations are approximately 1 hour. The extreme tail loading observed at Mercury implies that the relative intensity of substorms must be much larger than at Earth. The correspondence between the duration of tail field enhancements and the characteristic time for the Dungey cycle, which describes plasma circulation through Mercury's magnetosphere, suggests that such circulation determines the substorm time scale. A key aspect of tail unloading during terrestrial substorms is the acceleration of energetic charged particles, but no acceleration signatures were seen during the MESSENGER flyby.
authors.affiliation: Heliophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA. james.a.slavin@nasa.gov
authors.forename: James A
authors.initials: JA
authors.lastname: Slavin
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Anderson
authors.forename: Daniel N
authors.initials: DN
authors.lastname: Baker
authors.forename: Mehdi
authors.initials: M
authors.lastname: Benna
authors.forename: Scott A
authors.initials: SA
authors.lastname: Boardsen
authors.forename: George
authors.initials: G
authors.lastname: Gloeckler
authors.forename: Robert E
authors.initials: RE
authors.lastname: Gold
authors.forename: George C
authors.initials: GC
authors.lastname: Ho
authors.forename: Haje
authors.initials: H
authors.lastname: Korth
authors.forename: Stamatios M
authors.initials: SM
authors.lastname: Krimigis
authors.forename: Ralph L
authors.initials: RL
authors.lastname: McNutt
authors.forename: Larry R
authors.initials: LR
authors.lastname: Nittler
authors.forename: Jim M
authors.initials: JM
authors.lastname: Raines
authors.forename: Menelaos
authors.initials: M
authors.lastname: Sarantos
authors.forename: David
authors.initials: D
authors.lastname: Schriver
authors.forename: Sean C
authors.initials: SC
authors.lastname: Solomon
authors.forename: Richard D
authors.initials: RD
authors.lastname: Starr
authors.forename: Pavel M
authors.initials: PM
authors.lastname: Trávnícek
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Zurbuchen