EPSC Abstracts Vol. 14, EPSC2020-68, 2020 https://doi.org/10.5194/epsc2020-68 Europlanet Science Congress 2020 © Author(s) 2021. This work is distributed under the Creative Commons Attribution 4.0 License.
What lies immediately outside of the heliosphere in the very local interstellar medium (VLISM): What will ISP detect?
Jeffrey Linsky1 and Seth Redfield2 1University of Colorado, JILA, Boulder CO, United States of America ([email protected]) 2Wesleyan University, Astronomy Department, Middletown CT, United States of America ([email protected])
The Interstellar Probe (ISP) will provide the first direct measurements of interstellar gas and dust when it travels far beyond the heliopause where the solar wind no longer influences the ambient medium. We summarize in this presentation what we have been learning about the VLISM from 20 years of remote observations with the high-resolution spectrographs on the Hubble Space Telescope. Radial velocity measurements of interstellar absorption lines seen in the lines of sight to nearby stars allow us to measure the kinematics of gas flows in the VLISM. We find that the heliosphere is passing through a cluster of warm partially ionized interstellar clouds. The heliosphere is now at the edge of the Local Interstellar Cloud (LIC) and heading in the direction of the slighly cooler G cloud. Two other warm clouds (Blue and Aql) are very close to the heliosphere. We find that there is a large region of the sky with very low neutral hydrogen column density, which we call the hydrogen hole. In the direction of the hydrogen hole is the brightest photoionizing source, the star Epsilon Canis Majoris (CMa). Extreme ultraviolet photons from this star produce a Stromgren sphere region of ionized gas as large as the Local Cavity (extending to 100-200 parsecs) and produce Stromgren shells at the outer regions of the local warm clouds including the LIC.
When the ISP passes beyond the hydrogen wall at a distance of about 500 AU, it will likely enter the outer edge of the LIC where photoionization from Epsilon CMa plays an important role. Analysis of Hubble observations of interstellar absorption proves estimates of the densities, temperature, pressure, and flow properties of the main portion of the LIC, but we have little informtion on these properties at the LIC's edge. Comparison with the inflow vector of neutral helium measured by IBEX and Ulysses indicates a slightly different flow speed and direction than the mean flow of the LIC gas. ISP will provide direct measurements of the flow and gas properties of this poorly understood region. In particular, ISP will provide information on how photoionization from Epsilon CMa influences warm clouds through ionization, heating, and perhaps pressure balance. This information may resolve questions concerning the magnetic field surrounding the heliosphere. Powered by TCPDF (www.tcpdf.org)