Scientists solve mystery of disappearing sunspots

An image of a sunspot take by the Hinode Satellite is shown in ths undated NASA photo released to Reuters March 2, 2011.

SALMON, Idaho (Reuters) - A trio of top solar scientists said on Wednesday they had solved the mystery behind the disappearance of sunspots, a phenomenon that has stumped astrophysicists worldwide for more than two centuries.

The research, which will be published on Thursday in the journal Nature, shows that unusually weak magnetic fields on the sun paired with reduced solar activity cause sunspots to disappear.

Sunspots appear to the human eye as dark spots on the sun, some as wide as 49,000 miles, according to NASA. They are caused by intense magnetic activity, or storms, on the sun's surface, which is plasma. Sunspots often emit particles into space which are known as solar flares.

Sunspots went missing from 2008 to 2010 in a rare occurrence that first was reported in 1810.

Although it is well documented that the sun goes through regular 11-year cycles of high and low solar activity, sunspots are not prone to disappear for an extended period, the researchers said.

"Understanding sunspots is important because solar activities influence space weather, which affects technology in space and on the earth," Montana State University solar physicist Piet Martens, who conducted the study with two other scientists, said in a statement.

For example, the absence of sunspots in 2009 caused cosmic radiation to skyrocket, researchers found. Exposure to such high-energy radiation could prove dangerous to astronauts and long-range pilots, who can protect against solar flares but not cosmic rays, according to NASA.

Martens and a team of researchers used space telescopes to gather information about the sun's surface, documenting sunspots, solar flares and the strength of magnetic fields at the north and south poles of the sun.

Using computers to model the sun's surface over 2,000 years, the team tracked a link between an absence of sunspots and weak polar fields.

The finding opens the way for scientists to predict the magnitude of lulls in solar activity by examining the polar fields.

Lapses in solar activity reduce solar winds, preventing the decay of space junk like defunct satellites and parts of rockets. Those items place at risk orbiting satellites that provide signals for everything from cell phones to national defense systems.

Scientists said the ability to better forecast extreme lows in solar activity, like the disappearance of sunspots, could help protect communication systems by altering the orbits of satellites or shutting down sensitive systems.

(Editing by Dan Whitcomb and Greg McCune)