Cassini ENA (E > 5 keV) Heliosphere Belt and overlapping in-situ Voyager measurements: Pressure and ISMF implications

Details Cassini ENA (E > 5 keV) Heliosphere Belt and overlapping in-situ Voyager measurements: Pressure and ISMF implications Cassini ENA (E > 5 keV) Heliosphere Belt and overlapping in-situ Voyager measurements: Pressure and ISMF implications

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsh23d..06k&link_type=abstract

American Geophysical Union, Fall Meeting 2010, abstract #SH23D-06

Physics

[2114] Interplanetary Physics / Energetic Particles, [2124] Interplanetary Physics / Heliopause And Solar Wind Termination, [2126] Interplanetary Physics / Heliosphere/Interstellar Medium Interactions, [2151] Interplanetary Physics / Neutral Particles

Scientific paper

Maps of energetic neutral atoms (ENA) of the heliosphere from Cassini (Krimigis et al, 2009) have been constructed spanning the energy range ~ 5 ≤ E ≤ 55 keV, and show a “Belt” in the sky of ~ 100° FWHM. ENA maps < 6 keV have been obtained by the IBEX mission (McComas et al, 2009) and show a “Ribbon” that is narrower than the Belt and inclined to it in both ecliptic latitude (~25°) and longitude (~30°). The overlap in energy between Voyager ions (Decker et al, 2009) and Cassini ENA intensities (averaged over the ENA line of sight) enables us to deduce ion fluxes in the heliosheath, thus providing a continuous spectrum 5 ≤ E ≤ 4000 keV. The Cassini ENAs provide a smooth transition spectrum between the accelerated pickup ions (PUI) and the well-established Voyager LECP j∝E-1.5 tail at E > 28 keV, and lead to a thickness of the heliosheath of ~ 50 AU. These measurements are then used to estimate the local partial pressure over this energy range (~ 0.1 pPa), suggesting β > 25 locally. Using a simulated PUI distribution (Giacalone and Decker, 2010) we estimate the E < 6 keV contribution to the pressure to be ~ 0.12 pPa. Assuming constant total pressure throughout the heliosheath, the balance of the non-thermal pickup ion (PUI) pressure against the stagnation pressure of the interstellar plasma and the hydrostatic pressure of the local interstellar magnetic field (ISMF) at the nose of the heliopause implies an upper bound on the ISMF of ~ 0.64 nT. Implications on the shape of the heliosphere are discussed.

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