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The Heliosphere

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The rather mysterious astronomical structure known as the heliosphere is a solar magnetic bubble that protects our system from interstellar radiation. We don’t know much about it, and what we do know is still fragile. We do know that it changes at increasing distance from the Sun, with areas known as ‘structures’, which are regions where the solar wind and magnetic fields change either in density and/or speed. And according to data from Voyager 1 when it crossed the heliopause into interstellar space, it is 121 AU in diameter. Given the lack of data, models need to be revised again and again after observation and studies.


One such long study was carried out by Cassini, with added data from Voyager 1 and IBEX. It looked at ions trapped in Saturn’s magnetosphere, which come from solar particles that traveled out from the Sun and then ‘bounced back’ after interacting with atoms of interstellar gas. This process takes years, and thus the study was carried out over a solar 11 year activity cycle. It was suspected at that time that the heliosphere would be comet-shaped rather than spherical as it travelled through space, due to the influence of the interstellar medium. However scientists were surprised to find that atoms reflected back from the theorized tail of the heliosphere came back almost as fast as the ones from the nose, indicating that the heliosphere maintains it’s spherical shape. Why this should be is yet unclear, but it is possible that the stronger than expected interstellar magnetic field may have something to do with it. A paper on the Cassini results was Published in Nature Astronomy on April 24, 2017.


The current heliosphere model-- NASA, Dialynas, et al.

The current heliosphere model - NASA, Dialynas, et al.


Another model that didn’t prove to be correct was the idea of a ‘bow shock’. For years the heliosphere was modeled with a bow shock at the front as it slammed through the interstellar medium. However NASA’s Interstellar Boundary Explorer (IBEX) satellite revealed in 2012 that the Sun is moving around the galaxy 11,000 km/h or 7,000 mph slower than thought. So the speed of the heliosphere in interstellar space isn’t fast enough to create a shock, but is fast enough to create a wave. This is potentially good news as it puts less pressure on our protective bubble.


We still have much to learn about the heliosphere. NASA is now keen to send more interstellar probes out, which will give us further data on the way. The only issue for you and me is that further discoveries may be quite a few years or decades from now. In the meantime Voyager 2 will carry on exploring and sending back relevant data for a few more years before heading out into interstellar space.



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