Exploration of the Outer Heliosphere and the Local Interstellar Medium A Workshop Report (2004) / Chapter Skim
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2 Science Summary: The Interaction of the Solar Wind and the Local Interstellar Medium
2 Science Summary: The Interaction of the Solar Wind and the Local Interstellar Medium
Pages 7-23
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From page 7... ...
The term "boundaries" is used interchangeably in this report to refer both to specific boundaries, such as the termination shock or heliopause, and to regions enclosed by the boundaries, such as the inner and outer heliosheath, which would more properly be referred to as the heliospheric boundary regions. The context should make clear the word's meaning.
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From page 8... ...
and high-energy galactic cosmic rays contribute very rare elements, such as Be and B Consequently, the abundance of elements and isotopes changes over time, and knowledge of it for several points in time will allow us to understand nucleosynthetic evolution.
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From page 9... ...
Nonetheless, the mutual feedback between these disparate scales serves to determine almost all aspects of heliospheric physics. In many respects, the complex coupling between the solar wind and the interstellar medium is the quintessential example of multiscale, regional, and disparate populations (solar wind plasma, pickup ions, anomalous and galactic cosmic rays, neutral atoms)
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From page 10... ...
Whereas solar wind and interstellar plasmas respond to electromagnetic fields (being decelerated at the heliospheric boundary shocks, for example) , interstellar neutrals flow relatively unimpeded.
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From page 11... ...
Beyond this, the solar wind is turned toward the heliotail, carrying with it the spiraling interplanetary magnetic field.The heliopause separates solar material and magnetic fields from interstellar material and magnetic fields.Interstellar neutral atoms and higherenergy galactic cosmic rays can penetrate the heliosphere,but interstellar ions are diverted around it.Beyond the heliopause there may also be a bow shock formed in the interstellar medium. SOURCE: Jet Propulsion Laboratory (1999a)
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From page 12... ...
Charge exchange between the coupled, nonequilibrated neutral and charged particle populations can therefore introduce distinct new populations of neutral atoms and plasma whose characteristics reflect their parent population.The subsequent interaction and assimilation of the newly created plasma and neutral populations into the existing plasma and neutral distributions may then lead to the substantial modification of the overall partially ionized plasma system.Thus, the total neutral distribution cannot relax to a single Maxwellian distribution, and either a multicomponent transport (Zank et al., 1996a) or a kinetic description for the neutral populations (Baranov and Malama, 1993; Izmodenov et al., 1999; Müller et al., 2000)
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From page 13... ...
the density distribution of neutral hydrogen. The plasma boundaries, termination shock, heliopause, and bow shock are labeled, and the wall of neutral hydrogen is also identified.The solid lines of the top plot show the streamlines of the plasma.The plasma temperature is plotted logarithmically and the neutral density linearly.
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From page 14... ...
. Pickup ions act to weaken interplanetary shocks, even when magnetic fields (Rice and Zank, 1999)
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From page 15... ...
-- the pickup ion data can then be used to infer the neutral parameters at the heliospheric termination shock or possibly even beyond, depending on the importance of filtration. Similarly, the ACE SWICS and Solar Wind Ion Mass Spectrometer (SWIMS)
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From page 16... ...
Pickup He+ b 1.5 ± 0.15 Ulysses/SWICS (Solar Wind Ionic Composition Spectrometer) Pickup He++ b 1.5 Ulysses/SWICS Directc 26.3 ± 0.4 1.5 ± 0.3 6,300 ± 340 Ulysses/GAS (Energetic Particle and Interstellar Neutral Gas Experiment)
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From page 17... ...
Because many stars with a magnetic field and a stellar wind are surrounded by a partially ionized interstellar medium like that surrounding our heliosphere, much of the physics that we are learning locally about neutral atoms, pickup ions, anomolous cosmic rays, and so forth will carry over to the astrospheres of other stars. The deceleration and accumulation of neutral hydrogen on the upwind side of the heliosphere and other astrospheres have already led to the identification of hydrogen walls in both our own solar system and at several nearby star systems,using typical absorption features in the Lyman-alpha profile (Linsky,1996;Wood et al., 2000a,b)
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From page 18... ...
It is generally accepted that ACRs are formed when a fraction of the interstellar pickup ion population4 is injected into the diffusive shock acceleration process at the solar wind termination shock (Fisk et 4There is a possibility that, besides the interstellar source, there is another source of ACRs in the outer heliosphere. This "`outer source' is thought to consist of atoms that are sputtered from small grains of material from the Kuiper Belt.
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From page 19... ...
To study such behavior quantitatively and to draw inferences about acceleration processes in the outer heliosphere, pickup ion, suprathermal, and energetic particle populations need to be observed at 1 to 5 AU with elemental and ionic charge resolution and a collection power comparable to those of the energetic particle instruments on ACE. By following the acceleration of particles in CIRs and coronal mass ejections at increasing distances from the Sun, it will be possible to delineate the injection and preacceleration processes necessary to understand particle acceleration at the termination shock.
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From page 20... ...
It is conceivable, too, that the LISM magnetic field can be probed indirectly via cosmic rays, again provided that the spacecraft is sufficiently deep within the boundary region.
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From page 21... ...
. This radiation provides an opportunity to probe the outer boundaries and plasma characteristics of the solar system remotely, including the heliopause region where the solar wind plasma and LISM plasma interact (as distinct from the interstellar neutral atoms and the solar wind plasma)
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From page 22... ...
Considerable interest has been expressed in using ENA imaging, which has been successfully employed on the IMAGE mission, to image the termination shock and regions beyond. High-sensitivity ENA observations will help constrain global models of the heliosphere and will advance our theoretical understanding of the nature of the termination shock and the pickup ion population in the heliosheath.
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From page 23... ...
The interstellar magnetic field is oriented 20° from the interstellar flow direction and the interstellar magnetic field strength is assumed to be 1.6 µG. Density isolines are plotted in the meridional plane, together with three-dimensional steamlines starting in this plane.SOURCE: Pogorelov et al.
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