Expert: James Gort - 4/12/2007

Question
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: Hi Feivel.

We've "known" about the heliosheath (theoretically) at least from the late 1950's.  In 1957, S. Chapman developed a model of the corona which showed high temperatures and appreciable densities very far from the photosphere.  This helped Eugene Parker in 1958 to develop his hydrodynamical model of a continuously expanding coronal plasma (the solar wind).  Mariner 2 (in 1962) confirmed the solar wind's speed and particle density.   The Parker model indicated the existence of a heliosphere, one part of which is the heliosheath.  In 1992, indirect evidence of the heliosheath came from both Voyagers 1 and 2, when radio noise (at 1.8 to 3.5 kHz) was detected, and interpreted as the solar wind particles colliding with interstellar medium.  But there was no direct evidence of the heliosheath until December 2004 (and early 2005), when Voyager 1 encountered a significant increase in the strength of the magnetic field carried by the solar wind.  This is a direct consequence of the slowing down of solar wind particles when they collide with the interstellar medium.

The heliosheath does protect earth from some galactic cosmic rays, some of which are very energetic.  If it did not exist, I would guess that our upper atmosphere could be disturbed (including the ionosphere and ozone layer), and radio communications on earth could be more frequently interrupted.  Auroras would be more common.  Occasionally, we could experience a cosmic ray storm which would more directly affect terrestrial life, including an increase in cancers.  

I hope that helps answer your question.

Prof. James Gort

---------- FOLLOW-UP ----------

QUESTION: youre not accepting ratings?
sorry
but your answer was perfect in every way

Answer
Hi Feivel,

Thanks very much.  That's the sort of feedback I'll accept!

Actually, I was accepting feedback for years, but decided now to decline it.  I always do my best to accurately answer questions, and if I can't, I'll say so.  Some questions (like your second part) require some speculation or opinion, and I'll give the best informed one I can, but it may differ from others' opinions.  That may affect the ratings, which doesn't seem fair.

I realize that people who ask questions may look for high feedback ratings to get the best answers they can.  That's perfectly understandable.  But it's a tradeoff.  That benefit for questioners versus the possibility of inaccurate ratings.

I guess this reflects my overall philosophy regarding "grades".  I've always felt people should learn from courses, and not just shoot for high grades.  As a teacher, it's often hard to choose between a student earning a B or C, much less a number grade - the difference between a 68 and 70 may be lost in the noise!  Did the person have a bad day?  Misread the question?  When I was in school, some of my most memorable courses (and the ones I got the most from) were simply pass-fail.

So that's my philosophy in a nutshell.  I hope I don't lose questioners because I've opted out of the rating system.   But I do appreciate the personal note.

Cheers,

Prof. James Gort