Bursting The Sun's Bubble

Posted on: Oct 20, 2009

The IBEX satellite maps the boundary layer of the sun's bubble, or heliosheath. This map shows this data plotted on an all-sky image, revealing the bright ribbon-like structure (in greens, yellows and reds) swirling across the sky.

Image: Southwest Research Institute

The sun's environment in interstellar space — the heliosphere — is essentially a bubble that encompasses the entire solar system and has a diameter about 100 times the distance from the Earth to the sun. This region, in which the solar wind dominates before it smashes into the surrounding galactic gas and dust, was supposed to look something like the shape of a comet: a region pushed inward on one side and streaming outward on the other. But a new NASA orbiting observatory designed to study this vast zone found something completely different.

Our sun's sphere of influence, according to a series of papers published in Science on Oct. 16 detailing the initial results from the Interstellar Boundary Explorer (IBEX) satellite, seems instead to be a bubble that is cinched at the waist by a vast ribbon as seen by energetic neutral atoms — atoms that are not electrically charged, but are moving very fast through space — that are glowing 10 times more brightly than anyone had expected from anything in this region called the heliosphere. The textbook descriptions of the heliosphere, according to Science's accompanying news story, will have to be entirely rewritten.

IBEX is a project run by the Southwest Research Institute that involves dozens of researchers from several institutions around the country, including three from MIT who are co-authors of the group of Science papers: Peter Ford, a principal research scientist at the Kavli Institute for Astrophysics and Space Research, and Kavli research scientists Roland Vanderspek and Geoffrey Crew.

IBEX, launched a year ago into a high elliptical orbit that takes it out almost as far as the moon, has completed its first six months of observations — enough to give a first view of the entire sky. It captures energetic particles coming from the boundary between the sun's region of influence and the interstellar space beyond. Previously, the only direct evidence about this giant bubble came from the two Voyager spacecraft, which reached the inner edge of this boundary zone about two years ago and provided in-situ glimpses of two particular points on that shell.

IBEX provides 'the first all-sky view of this region, and no one was expecting what we've seen,' Crew says. Oddly enough, the energetic ribbon that circles the whole sky doesn't seem to follow the ecliptic (the plane in which all of the planets orbit). Nor does it follow the plane of the galaxy we inhabit, the Milky Way. 'Who ordered this?' Crew exclaims. 'It doesn't line up with anything!'

What does the discrepancy mean? It will take theorists some time to figure that out, since the observations were so different from anything predicted by existing theories or models. 'Theories are flying,' Crew says. One suggestion is that the ribbon of energetic neutral atoms may have to do with the effect of the local galactic magnetic field pushing against the heliosphere. These observations suggest that the ribbon is perpendicular to that magnetic field, he says.

IBEX is expected to remain in operation for at least two more years, and it could potentially keep going for a decade or more if funding is provided, which would be helpful in order to see whether the heliosphere varies over the course of the 11-year solar cycle. 'There's a lot to look at in the future to try to understand this,' Crew says. 'There will be a wealth of new information to constrain the models.'

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