5. Very Local Interstellar Medium and the Solar Cycle in the Heliosphere

Figure 3

[18]  The general characteristics of the heliosphere, its dimensions, the form of the main surfaces, etc., depend heavily on the properties of the very local interstellar medium, surrounding the heliosphere in the Galaxy. Consequently many properties of the near-Earth space would be quite different from the present ones if the Sun were a trifle off its present position, the fact often forgotten in formulating the list of the cosmic factors important for the Earth. Figure 3 from Bochkarev [1990] illustrates the position of the Sun with respect to the Scorpion-Centaurs (SCO-CEN) stellar association which center is

Figure 4

about 170 Pc from the Sun, while Figure 4 from Bochkarev [1990] shows much nearer solar area surroundings, namely, the Sun's position with respect to the local HI cloud (about 10 Pc from the Sun) and the dense Sancini-van Woerden filament inside it.

[19]  We shall not go into detail [see Bochkarev, 1990], just mention that now the Sun is in the worm (temperature T 104 K) and rather rare (density n 10^-1 cm ^-1 ) weakly ionized hydrogen, the heliospheric dimensions being about 200 AU. If the Sun shifted to the SCO-CEN association by about 10-20 Pc (compare with the 10 kPc distance from the center of the Galaxy!) it would be surrounded by 2 order of magnitude denser and colder hydrogen and there is even a possibility that the whole heliosphere could be inside the Earth's orbit, and the Earth would be without any solar wind, the solar cycle and other GCR variations etc.! If somebody shifted the Sun 10-20 Pc more it would be in the SCO-CEN cavity with highly rarefied ( n 10^-3 cm ^-1 ) and hot ( T 106 K) gas and the dimensions of the heliosphere could be much greater than now. Then the phase shift of the solar cycle in the inner and outer parts of the heliosphere would be great and the solar cycle in the GCR intensity would look quite different from how it looks now [see Krainev and Webber, 2004].