Sun May Be Built Like an Onion, Scientist Says

The sun may consist of onion-like layers of gas that spin at their own rates, and even small deviations in the amount of energy in the layers could mean the difference between Earth’s frying or freezing, a scientist said.

“Activity within the sun’s various layers may well be a key factor in the Earth’s climate,” University of Southern California astronomer Edward Rhodes said. “Though we take the sun’s energy output for granted, a change in that output of just a fraction of 1% could make the difference between our freezing or frying.”

Rhodes said his preliminary studies may ultimately lead to methods of predicting how changes that occur in the sun’s interior affect Earth’s climate as well as helping scientists more precisely determine when the giant star will burn out.

Some studies suggest that the 864,000-mile-wide star rotates as a single mass without separate rotation rates for inner solar structures. But emerging data is establishing rotation rates for the surface, which is mostly helium, down to its hydrogen core.

“Our observations tend to support an emerging view of the sun as a rotating spherical shell containing three separately rotating shells,” Rhodes said. “It’s concentric, like the layers of an onion or a child’s toy, with a series of spherical shells encompassing a smaller shell until you reach the smallest, which is the core.”

Studies under way at USC and the Jet Propulsion Laboratory in Pasadena are demystifying some of the unknown aspects of the sun’s structure by way of helioseismology--investigations equivalent to the studies of earthquakes.

Those investigations are providing scientists with new data on the the role of the layers and their movement over specified intervals of time.

“The surface layer, the photosphere, is where the light that we see from the sun escapes,” Rhodes said. “The next layer down is the so-called convection zone where the heat is transferred to the surface through gas motion, much as heat is transferred from the bottom to the top of a boiling pot of water. The radiative zone is beneath that and then the core.”

The new studies show that the photosphere, which occupies less than a thousandth of the sun’s radius, rotates about every 25 days at the sun’s equator and about every 36 days near the poles.

He said that the convection zone rotates somewhat faster than the photosphere and that the rate for the radiative zone is slower than the rotation rate of the surface.

“We’re now about to test other scientists’ observations that the sun’s core--the innermost sphere--rotates in as little as 12 days or less,” Rhodes said.

He said the studies from a 60-foot solar telescope also are focusing on the magnetic storms called sunspots that sometimes appear on the sun’s surface and affect the climate on Earth.

“Though we refer to an 11-year sunspot cycle, we haven’t really narrowed it down much within a range of seven to 17 years,” he said. “The possibility of sunspot prediction would seem to depend on our learning more about subsurface solar dynamics.”

Rhodes said that as far as solar astronomers can determine, the sun will completely burn out within the next 4 1/2 billion years.

“We’re now halfway through the sun’s stable phase of existence. At some point in the future, the surface layers of the sun will swell outward and possibly engulf the Earth,” he said.