Pickup Ions and Cosmic Rays from Dust in the Heliosphere |
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Authors: | N A Schwadron G Gloeckler |
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Institution: | (1) Department of Astronomy, Center for Spaceweather Modeling, Center for Space Physics, Boston University, Commonwealth Ave 725, Boston, MA 02215, USA;(2) Department of Atmospheric, Oceanic and Space Science, University of Michigan, Hayward St 2455, Ann Arbor, MI 48109-2143, USA |
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Abstract: | The combination of recent observational and theoretical work has completed the catalog of the sources of heliospheric Pickup
Ions (PUIs). These PUIs are the seed population for Anomalous Cosmic Rays (ACRs), which are accelerated to high energies at
or beyond the Termination Shock (TS). For elements with high First Ionization Potentials (high-FIP atoms: e.g., H, He, Ne,
etc.), the dominant source of PUIs and ACRs is from neutral atoms that drift into the heliosphere from the Local Interstellar
Medium (LISM) and, prior to ionization, are influenced primarily by solar gravitation and radiation pressure (for H). After
ionization, these interstellar ions are pickup up by the solar wind, swept out, and are either accelerated near the TS or
beyond it. Elements with low first ionization potentials (low-FIP atoms: e.g., C, Si, Mg, Fe, etc.) are also observed as PUIs
by Ulysses and as ACRs by Wind and Voyager. But the low-FIP composition of this additional component reveals a very different
origin. Low-FIP interstellar atoms are predominantly ionized in the LISM and therefore excluded from the heliosphere by the
solar wind. Remarkably, a low-FIP component of PUIs was hypothesized by Banks (J. Geophys. Res. 76, 4341, 1971) over twenty years prior to its direct detection by Ulysses/SWICS (Geiss et al., J. Geophys. Res. 100(23), 373, 1995) The leading concept for the generation of Inner Source PUIs involves an effective recycling of solar wind on grains near
the Sun, as originally suggested by Banks. Voyager and Wind also observe low-FIP ACRs, and a grain-related source appears
likely and necessary. Two concepts have been proposed to explain these low-FIP ACRs: the first concept involves the acceleration
of the Inner Source of PUIs, and the second involves a so-called Outer Source of PUIs generated from solar wind interaction
with the large population of grains in the Kuiper Belt. We review here the observational and theoretical work over the last
decade that shows how solar wind and heliospheric grains interact to produce pickup ions, and, in turn, anomalous cosmic rays.
The inner and outer sources of pickup ions and anomalous cosmic rays exemplify dusty plasma interactions that are fundamental
throughout the cosmos for the production of energetic particles and the formation of stellar systems. |
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Keywords: | Heliosphere: anomalous cosmic rays Heliosphere: pickup ions Sun: inner source Sun: dust populations |
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