Sun: Just Warming Up Now

June 18, 2009 -- Scientists have been puzzled by the lack of sunspots on the surface of the sun. But now they may have figured out an explanation.

A slow-moving river of gas snaking deep within the sun's interior took longer than expected to reach the critical zone where sunspots are born.

Normally, sunspots reappear about every 11 years at the start of a new cycle of solar activity. Last year, the sun was spot-free for 266 days of the year, marking the quietest period of solar activity in a century.

Already this year, the sun has had 131 spotless days.

Frank Hill, a scientist with the National Solar Observatory in Tucson, Ariz., explained it may be the sun is just now poised for more activity.

"It's now moving into position where we have observed sunspots begin to appear in the past," Hill said at an American Astronomical Society meeting in Colorado this week.

By monitoring ripples in the sun's surface, scientists have been able to figure out what is happening in its interior, similar to how doctors use sonograms to see inside the body.

Related Content:

• My Take: What's Wrong With Our Sun?
• HowStuffWorks.com: Sun
• Wide Angle: Solar Minimum
• More Discovery News

They found a jet stream 4,000 miles beneath the sun's surface that has been moving at a snail's pace from the polar region of the sun to its equatorial zone. During the last solar cycle, it took two years for the jet stream to cover a 10 degree range in latitude. This cycle, it took three years to cover the same geography.

"We believe that the sluggishness of this flow explains the (prolonged) solar minimum," Hill said.

"It is not clear whether this flow is a cause of the sunspot cycle or a consequence of it ... but I believe it is a cause," he added. "We need to continue these observations for many, many, many, many, many more years in order to fully understand what is going on."

The sun creates new jet streams near its poles every 11 years. The streams migrate over a period of 17 years to the equator. Once they reach 22 degrees latitude, sunspots are born.

Scientists monitor sunspots to forecast solar geomagnetic storms, which can impact satellites, power systems, radio communications and other technologies on Earth. The storms also trigger high levels of radioactivity that can pose a health risk to astronauts living on the space station beyond Earth's protective atmosphere.

"When the next solar minimum and the next solar maximum will occur has been poorly predicted," added Dean Pesnell, with NASA's Goddard Space Flight Center in Greenbelt., Md. "None of the forecasting research groups actually predicted the current long extended delay in the new cycle."

The late start of the new solar cycle prompted the U.S. panel tasked with making space weather forecasts to revise its prediction, with a new solar maximum now pegged for May 2013.

Related Links:

Slide Show: Hottest Solar Images

National Solar Observatory

Irene Klotz's Blog: Free Space

Discovery Space for news, interviews and more.