WASHINGTON, Oct. 2 (UPI) -- U.S. space agency scientists say they have discovered the sun is not a perfect sphere.
The scientists said they used the National Aeronautics and Space Administration's RHESSI spacecraft -- the Reuven Ramaty High Energy Solar Spectroscopid Imager -- to measure the roundness of the sun with unprecedented precision. They discovered that it's not only not perfectly round, but during years of high solar activity the sun develops a thin "cantaloupe skin" that significantly increases its apparent oblateness -- the sun's equatorial radius becomes slightly larger than its polar radius.
"The sun is the biggest and therefore smoothest object in the solar system, perfect at the 0.001 percent level because of its extremely strong gravity," said study co-author Hugh Hudson of the University of California-Berkeley. "Measuring its exact shape is no easy task."
The scientists said further analysis of the data might help researchers detect a long-sought type of seismic wave echoing through the sun's interior: gravitational oscillation or "g-mode." The researchers said detecting g-modes would open a new frontier in solar physics -- the study of the sun's internal core.
The research is reported in the online journal Science Express.