Why is the Sun So Round?
The Sun rotates every 28 days, and because it doesn’t have a solid surface, it should be slightly flattened. This tiny flattening has been studied with many instruments for almost 50 years to learn about the Sun’s rotation, especially the rotation below its surface, which we can’t see directly.
Now Jeff Kuhn and Isabelle Scholl (Institute for Astronomy, University of Hawaii at Manoa), Rock Bush (Stanford University), and Marcelo Emilio (Universidade Estadual de Ponta Grossa, Brazil) have used the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory satellite to obtain what they believe is the definitive -- and baffling -- answer.
They also found that the solar flattening is remarkably constant over time and too small to agree with that predicted from its surface rotation. This suggests that other subsurface forces, like solar magnetism or turbulence, may be a more powerful influence than expected.
Kuhn, the team leader and first author of an article published today in Science Express, said, “For years we’ve believed our fluctuating measurements were telling us that the Sun varies, but these new results say something different. While just about everything else in the Sun changes along with its 11-year sunspot cycle, the shape doesn’t.”
The Sun plays a vital role in maintaining the habitability of Earth. Studying the Sun provides valuable information that could help astrobiologists determine where best to search for other potentially habitable worlds in the Universe.