Expert: Philip Stahl - 4/11/2007

Question

i just heard about the heliosheath.

i have two questions if you will, (not very easy ones, i fear)

1. how long have we known about the heliosheath?
2. can you hazard a guess as to the effect on the earth if the heliosheath did not exist?

thanks

feivel

Answer
Hello,

In theory at least, we have probably known about the heliosheath since the first advances made in defining the limits of the solar wind. Since the existence-validity of the solar wind was first shown by Eugene Parker in the 1950s, one could say the theoretical basis can be traced at least to that time.

In astronomy - actually more astrophysics and space physics - we use specialized terms to define the extent or limits of influence of various objects. These may take into account magnetic influence, as well as energy influence.

In the case of the Earth, we define the "magnetosphere" as the region of space around Earth wherein solar and terrestrial magnetic and electric effects abound. For example, the aurora occurs within this zone.

In a much larger scale, we define the "heliosphere" as the bubble of influence created by the solar wind. (This is the high speed wind that sweeps outwards from the Sun).

The heliosheath occurs at the far edge of the heliosphere. More technically, it occurs between the "termination shock" and the "heliopause".

Thus, it marks a boundary at the edge of solar system space. In May 2005, NASA announced that Voyager 1 had crossed the termination shock and entered the heliosheath in December 2004, at a distance of 94 AU. (Astronomical Units). This means the observational basis for the heliosheath is now feasible.

As to question 2, the heliosheath would only cease to exist if the Sun itself ceased to exist - since it is the Sun's solar wind that defines the heliosphere, and as I noted the heliosheath defines its edge.

So we can say that no life on Earth would exist if the heliosheath did not exist, because no Sun would exist to form it in the first place!