An Overview of the Field and Plasma Environment of Jupiter and Saturn (and how an ionosphere can wag the tail and everything else)
Location
Yosemite National Park
Start Date
2-13-2014 10:15 AM
End Date
2-13-2014 10:45 AM
Description
Thinking back to the first Yosemite meeting in 1974 (a year marked by political and climatic turbulence), it is relevant to remind ourselves that only a few months earlier, in December 1973, Pioneer 10 became the first spacecraft to fly by a gas giant planet. Pioneer 11 would not reach Jupiter until the end of the year, after which it swooped by Saturn on its way towards the heliopause. Today we look back on decades of spacecraft exploration and groundbased observations during which we discovered the many ways in which the outer planet magnetospheres differ from Earth’s magnetosphere. The important (dimensionless) parameters of the solar wind change with distance from the Sun and that accounts for some differences. However, many other features of the planetary environments have consequences that can be surprising. Some of the important effects relate to: *Sources of heavy ion plasma The gas giant magnetospheres differ significantly from Earth’s magnetosphere because in addition to the sources of plasma familiar at Earth (solar wind, ionosphere) there are major sources of heavy ions in the equatorial inner magnetosphere. These heavy ions, spun up to some fraction of corotation, produce structure and dynamics that differ greatly from what is familiar at Earth. *Rotation At Earth, the speed of corotation matches the typical speed of solar wind-imposed convection inside of 10 RE, and well inside the magnetopause. At Jupiter, rotation speeds dominate solar wind-imposed convection even in the outer magnetosphere. The combination of rapid rotation and heavy ions implies that much of the plasma is interchange unstable and that plasma transport occurs in ways that are atypical for the terrestrial magnetosphere. One can also argue that much of the plasma loss to the solar wind occurs through processes that differ greatly from the type of magnetic reconnection-driven loss familiar at Earth. *Spatial and temporal scales In systems as large as the magnetospheres of Jupiter and Saturn, there are significant delays between input (of almost any sort) and response, purely related to the length of time it takes for signals to carry information over extremely long distances. These delays contribute to significant twists of the magnetic field and to warping of the tail current sheet. At very large distances, the ionosphere loses control of the magnetospheric plasma. *The role of ionospheric anomalies Perhaps it is not yet generally accepted, but there are good reasons to believe that ionospheric anomalies, arising either spontaneously or through coupling with the thermosphere, drive periodic perturbations through Saturn’s magnetosphere, thereby imposing periodic variations that we describe as rotating, breathing, and flapping. Such processes have not been observed in Earth’s magnetosphere. Although this abstract emphasizes ways in which the magnetospheres of the giant planets differ from Earth’s magnetosphere, one should recognize that the underlying laws are universal. The plasma and field properties of the magnetospheres of Jupiter and Saturn teach us lessons that may have applications to our own magnetosphere.
An Overview of the Field and Plasma Environment of Jupiter and Saturn (and how an ionosphere can wag the tail and everything else)
Yosemite National Park
Thinking back to the first Yosemite meeting in 1974 (a year marked by political and climatic turbulence), it is relevant to remind ourselves that only a few months earlier, in December 1973, Pioneer 10 became the first spacecraft to fly by a gas giant planet. Pioneer 11 would not reach Jupiter until the end of the year, after which it swooped by Saturn on its way towards the heliopause. Today we look back on decades of spacecraft exploration and groundbased observations during which we discovered the many ways in which the outer planet magnetospheres differ from Earth’s magnetosphere. The important (dimensionless) parameters of the solar wind change with distance from the Sun and that accounts for some differences. However, many other features of the planetary environments have consequences that can be surprising. Some of the important effects relate to: *Sources of heavy ion plasma The gas giant magnetospheres differ significantly from Earth’s magnetosphere because in addition to the sources of plasma familiar at Earth (solar wind, ionosphere) there are major sources of heavy ions in the equatorial inner magnetosphere. These heavy ions, spun up to some fraction of corotation, produce structure and dynamics that differ greatly from what is familiar at Earth. *Rotation At Earth, the speed of corotation matches the typical speed of solar wind-imposed convection inside of 10 RE, and well inside the magnetopause. At Jupiter, rotation speeds dominate solar wind-imposed convection even in the outer magnetosphere. The combination of rapid rotation and heavy ions implies that much of the plasma is interchange unstable and that plasma transport occurs in ways that are atypical for the terrestrial magnetosphere. One can also argue that much of the plasma loss to the solar wind occurs through processes that differ greatly from the type of magnetic reconnection-driven loss familiar at Earth. *Spatial and temporal scales In systems as large as the magnetospheres of Jupiter and Saturn, there are significant delays between input (of almost any sort) and response, purely related to the length of time it takes for signals to carry information over extremely long distances. These delays contribute to significant twists of the magnetic field and to warping of the tail current sheet. At very large distances, the ionosphere loses control of the magnetospheric plasma. *The role of ionospheric anomalies Perhaps it is not yet generally accepted, but there are good reasons to believe that ionospheric anomalies, arising either spontaneously or through coupling with the thermosphere, drive periodic perturbations through Saturn’s magnetosphere, thereby imposing periodic variations that we describe as rotating, breathing, and flapping. Such processes have not been observed in Earth’s magnetosphere. Although this abstract emphasizes ways in which the magnetospheres of the giant planets differ from Earth’s magnetosphere, one should recognize that the underlying laws are universal. The plasma and field properties of the magnetospheres of Jupiter and Saturn teach us lessons that may have applications to our own magnetosphere.