Local Interstellar Parameters as They Are Inferred from Analysis of Observations Inside the Heliosphere

Abstract

This paper provides a brief summary on the current knowledge of the properties of the Circum-Heliospheric Interstellar Medium (CHISM). It discusses what can be learnt on the parameters of CHISM's components from analysis of measurements performed inside the heliosphere. The analysis is based on the kinetic-gasdynamic models of the solar wind/interstellar medium interaction. We focus the analysis on three types of diagnostics: 1) interstellar H atom number density at the heliospheric termination shock inferred from pickup ion measurements, 2) the location and time of the Voyager 1 and 2 termination shock crossings, 3) the deflection of the interstellar H atom flow inside the heliosphere as been measured by SOHO/SWAN. From these results estimations of the unknown local interstellar parameters are deduced. The parameters are the number densities of interstellar H + and H and the magnitude and direction of the interstellar magnetic field in the vicinity of the solar system.

Observations of the Interplanetary Hydrogen During Solar Cycles 23 and 24. What Can We Deduce About the Local Interstellar Medium?

“…Models taking into account the obliquity of the LIMF showed a severe distortion of the heliosphere (Fahr et al 1988;Ratkiewicz et al 1998;Pogorelov & Matsuda 1998). These predictions were confirmed by a multi-observational approach: the deviation of the intensity maximum in the Lyα flux from the upwind direction as detected by Voyager 1/ Ultraviolet Spectrometer (Ben-Jaffel et al 2000), the deflection of the interstellar hydrogen flow with respect to the helium flow as observed by Solar and Heliospheric Observatory (SOHO)/ Solar Wind ANisotropy (SWAN; Lallement et al 2005Lallement et al , 2010Izmodenov et al 2005), the difference in the termination shock heliospheric distances detected by the Voyager 1 and Voyager 2 spacecraft (Ratkiewicz & Grygorczuk 2008;Izmodenov 2009;Pogorelov et al 2009;Opher et al 2009), and the ribbon of energetic neutral atoms around the heliosphere discovered by Cassini (Krimigis et al 2009) and IBEX ).…”

“…As the LIMF has been measured through a multi-observational approach (e.g., Lallement et al 2005;Izmodenov et al 2005;Ratkiewicz & Grygorczuk 2008;Izmodenov 2009;McComas et al 2009), this discrepancy suggests an unidentified weakness in the model.…”

Orbital apocenter is not a sufficient condition for HST/STIS detection of Europa’s water vapor aurora

“…The cross section for photoabsorption of Ly-α by H 2 O is σ ≈ 1:5 × 10 −17 cm 2 (49) and the optical depth for the derived average plume column density of 1:5 × 10 16 cm −2 (14) is thus τ ≈ 0:2. A potential attenuation of the ∼300-R IPM Ly-α background (Table 2) is therefore negligible compared with the 2012 emission brightness of 600 R. The optical depth due to scattering of Ly-α by the interplanetary hydrogen between Jupiter and Earth can approach values of τ ∼ 0:1, when Jupiter is at ecliptic longitudes near the IPM upstream direction of λ ≈ 252° (50,51). However, during all five previous STIS visits Europa was less than 40°from the IPM downstream direction (see ecliptic longitudes in Table 2), implying very low IPM optical depths.…”

Kinetic-Gasdynamic Modeling of the Heliospheric Interface

“…However, this variation can not completely account for the observed difference of 10 AU. As it has been argued in Izmodenov (2009), the most probable physical reason for this difference is the existence of a substantial interstellar magnetic field inclined to the direction of the interstellar gas flow with respect to the Sun. An indication of the inclined interstellar magnetic field was also found from analysis of backscattered Lyman-alpha radiation measured by the SWAN instrument on board of SOHO (Lallement et al 2005).…”