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An Introduction to, and Rationale for The Interstellar Probe
The heliosphere is that part of our galaxy which is swept by the solar wind.
The schematic above shows the heliosphere, with the locations of the planets shown for scale.
The heliopause in this picture marks the outer boundary of the heliosphere and it is the goal of The Interstellar Probe to go far beyond this boundary.
Measure the interstellar magnetic field and the density, temperature, and ionization state of the interstellar gas and their variations over a variety of temporal and spatial scales
Determine the interstellar spectra of galactic cosmic rays and their contribution to the ionization, heating, and dynamics of the interstellar medium.
Determine the mass and velocity distributions and the composition of interstellar dust
Measure the elemental and isotopic composition of interstellar plasma, neutral gas, unmodulated galactic cosmic rays, and their interaction products, and study their implications for galactic evolution and the origin of the solar system
Measure cosmic ray electrons and positrons and study their implications for galactic gamma ray production, recent nucleosynthesis, and interstellar radio emission
Determine the abundance of deuterium and He-3 in the local interstellar medium as constraints on Big Bang and galactic chemical evolution theories
Observe the cosmological infrared background radiation without contamination by emission from the Zodiacal dust
Investigate the location and motion of the termination shock and heliopause as it responds to solar variations and interstellar pressure
Investigate the structure of the termination shock, including the roles of thermal plasma, waves, pickup ions, and anomalous cosmic rays in determining the shock structure.
Search for evidence of a heliospheric bow shock
Determine the global properties and dynamics of the heliosphere with both in situ measurements and imaging.
Determine the properties of interstellar gas and dust that penetrate into the heliosphere
Study the deflection of the subsonic solar wind and interstellar plasma flows in the heliosheath, including the effects of thermal pressure gradients, magnetic fields, and the neutral interstellar gas.
Determine the influence of the interstellar medium on solar wind dynamics
Explore in situ the structure of the hydrogen wall and relate its properties to observations of similar structures and winds observed in neighboring stellar systems
Determine the scale of the heliosphere and the extent of its influence on the temperature, ionization state, and energetic particle environment of the local solar neighborhood.
Study the structure and dynamics of the outer heliosphere as an example of the interaction between a star and its environment.
Study, in situ, the acceleration of anomalous cosmic rays and other particle species at the termination shock and elsewhere.
Determine the composition and the mass and orbital distributions of dust in the outer solar system and identify creation and destruction mechanisms
Explore the structure of the Zodiacal dust cloud and its implications for infrared observations of the Galaxy, for the evolution of the solar system, and for studies of planets around other stars.
Search for dust structures associated with planets, asteroids, comets, and the Kuiper Belt, and determine the probable creation mechanisms
Determine the radial distribution of small Kuiper Belt objects
Determine the nature of organic matter in the outer solar system and the interstellar medium
This is a picture of how the heliosphere might look, similar to that above. There are many specialized terms that can be defined with this picture.
Heliopause: The boundary between solar wind plasma and interstellar plasma is called the “heliopause”.
Inner heliosheath: The region between the termination shock and the heliopause.
||One of the many unknowns is the strength of the magnetic
field in the interstellar medium. If the field is very weak, then it will
have little or no effect on the flow properties.
If the field is strong, it will influence how the heliosphere looks. An example of this is the shape of the termination shock and the heliopause.
The pictures above are both for a strong insterstellar magnetic field and the resulting termination shock is approximately spherical. This happens because the external flow speed against the heliosphere is less than the Alfven speed.
If the interstellar magnetic field is weak, then the termination shock can be greatly elongated in the direction of the heliotail because the speed of the flow speed against the heliosphere may be much more than the Alfven speed. This is depicted in the picture shown here.
Not only can the termination shock greatly elongated downstream, the
inner heliosheath would be relatively thin.
Using remote sensing of:
The Observing Objectives described in the next section address what the Interstellar Probe will do in more detail.
Go to Observing Objectives
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