EGU2020-1410
https://doi.org/10.5194/egusphere-egu2020-1410
EGU General Assembly 2020
© Author(s) 2020. 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): morphology of the Local Interstellar Cloud, its hydrogen hole, Stromgren Shells, and 60Fe accretion

Jeffrey Linsky
Jeffrey Linsky
  • University of Colorado, JILA, Boulder CO, United States of America (jlinsky@jila.colorado.edu)

 We describe the very local interstellar medium (VLISM)
immediately outside of the outer heliosphere. The VLISM consists 
of four partially ionized clouds - the Local Interstellar Cloud (LIC), 
G cloud, Blue cloud, and Aql cloud that are in contact with the outer 
heliosphere, and ionized gas produced by extreme-UV radiation 
primarily from the star Epsilon CMa. We construct the 
three-dimensional shape of the LIC based on interstellar line 
absorption along 62 sightlines and show that in the direction of 
Epsilon CMa, Beta CMa, and Sirius B the neutral hydrogen column 
density from the center of the LIC looking outward is a minimum. 
We call this region the ``hydrogen hole''. In this direction, the 
presence of Blue cloud absorption and the absence of LIC absorption 
can be simply explained by the Blue cloud lying just outside of the 
heliosphere. We propose that the outer edge of the Blue cloud is a 
Str\"omgren shell driven toward the heliosphere by high pressures in 
the H II region. The outer edges of other clouds facing Epsilon CMa 
are likely also Stromgren shells. Unlike previous models, the LIC
surrounds less than half of the heliosphere.

We find that the vectors of neutral and ionized helium flowing
through the heliosphere are inconsistent with the mean LIC flow 
vector and describe several possible explanations. The ionization
of nearby intercloud gas is consistent with photo-ionization by 
Epsilon CMa and hot white dwarfs without requiring additional 
sources of ionization or million degree plasma. In the upwind 
direction, the heliosphere is passing through an environment of 
several LISM clouds, which may explain the recent influx of 
interstellar grains containing 60Fe from supernova ejecta measured 
in Antarctica snow. The Sun will leave the outer partof the LIC 
in less than 1900 years, perhaps this year, to either enter the 
partially ionized G cloud or a highly ionized intercloud layer. 
The heliosphere will change in either scenario. An instrumented 
deep space probe sending back in situ plasma and magnetic field 
measurements from 500-1,000 AU is needed to understand the 
heliosphere environment rather than integrated data along the 
sightlines to stars.  

How to cite: Linsky, J.: What lies immediately outside of the heliosphere in the very local interstellar medium (VLISM): morphology of the Local Interstellar Cloud, its hydrogen hole, Stromgren Shells, and 60Fe accretion, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1410, https://doi.org/10.5194/egusphere-egu2020-1410, 2019

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