archive: SETI Re: [ASTRO] Pioneer 10 Update - December 1, 1998

SETI Re: [ASTRO] Pioneer 10 Update - December 1, 1998

Larry Klaes ( )
Tue, 22 Dec 1998 08:39:50 -0500

Here are some Web sites on the heliosphere which you may find useful:


At 09:01 PM 12/21/1998 -0500, Jega A.Arulpragasam wrote:
>>Neutron monitors on Earth (e.g., at Climax and Goose Bay) recorded a marked
>>and rapid decrease in cosmic ray intensity of about 4 % during April and
>>early May of 1998. If Pioneer 10 is still inside the heliopause, we can
>>expect a decrease in cosmic-ray intensity at Pioneer 10 to occur during
>>early 1999. The approximate 9 month delay from Earth to Pioneer 10
>>corresponds to the distance of 71 AU covered by the solar wind assuming a
>>speed of 450 km/s. If Pioneer10 has passed outside the heliopause into
>>interstellar space, then the decrease in cosmic intensity will not be
>>observed at Pioneer 10.
>Am I misreading this? This seems to imply that the decrease in cosmic
>ray intensity is due to the solar wind, and furthermore, that it occurs
>(almost) entirely at the heliopause.
>Two other alternatives spring to mind: 1. The reduction in the cosmic
>ray intensity is NOT (primarily) due to the solar wind, in which case,
>Pioneer 10 would observe the reduction in cosmic ray intensity, even
>outside the heliopause. (Is the variation of the cosmic ray intensity on
>Eart that well correlated to the solar wind characteristics, that we have
>high confidence that it would be constant, absent the solar wind?). 2.
>Nearly all the reduction in cosmic ray intensity takes place in the 70 AU
>between the spherical shells defined by the radii marked by the Sun-
>Pioneer and Sun-Earth distances. In this case, Pioneer could be within
>the heliopause, and still not observe the decrease in intensity.
>Why is neither of these alternatives viable?
>Finally, I wonder if anyone can help me with regard to the problem I'm
>having with the concept of the heliopause. I understand it to be where
>the incoming stellar wind from other stars, and the outgoing solar bring
>each other to a 'standstill.'
>It would seem to me naive to postulate spherical symmetry, centered on
>the Sun, with respect to the stellar wind. Making the simple-minded (but
>much less so) assumption that the stellar wind is in some fixed direction
>across the region around the solar system, wouldn't it be reasonable to
>expect the heliopause to take the kind of shape of the magnetospheres
>around the planets? In that case, the heliopause will be much closer at
>the bow, and much further at the stern, where the (stellar and solar)
>wind particles swept round the heliopuase combine to reform the stellar
>wind, with the Sun's contribution added.
>What is the model for the heliopause? What characteristics are expected
>to be found at this boundary? What, if anything, can observations from
>one or two probes tell us about the orientation of the 'axis of the
>Mystified in Massachusetts.
>Jega A. Arulpragasam <>
>Lunenburg, MA
>42 deg 36'N; 71 deg 43'W