Mysterious Speed Record May Explain Mystery of Sun (SPACE.com)

A new study reports that the top of the

gigantic conveyor belt of plasma moving inside the sun has been running at

record-high speeds for the past five years.

The phenomenon might be the reason why the

sun has continued to have so few sunspots recently when it should be ramping up

the production of these surface-blotching storms. 

"I

believe this could explain the unusually deep solar minimum we've been

experiencing," said David Hathaway, a solar physicist at NASA and

co-author of a new study describing the findings, in a NASA statement. "The high speed of the

conveyor belt challenges existing models of the solar cycle and it has forced

us back to the drawing board for new ideas."

The so-called Great Conveyor Belt is a

massive circulating current of hot plasma within the sun. It has two branches,

north and south, each taking about 40 years to complete one circuit.

Researchers believe the turning of the belt controls the sunspot cycle.

Hathaway has been monitoring the conveyor

belt using data from the Solar and

Heliospheric Observatory (SOHO). The top of the belt skims the surface of

the sun, sweeping up knots of solar magnetism and carrying them toward the

poles.

SOHO is able to track those knots — Hathaway

called them "magnetic elements" — and thus reveal the speed of the

underlying flow.

"It's a little like measuring the speed

of a river on Earth by clocking the leaves and twigs floating downstream,"

Hathaway explained.

SOHO's dataset extends all the way back to

1996 and spans a complete solar cycle.

Last year, Lisa Rightmire, a student of

Hathaway from the University of Memphis, spent the entire summer measuring

magnetic elements. When she plotted their speeds versus time, she noticed how

fast the conveyor belt has been going.

A note about "fast": The Great

Conveyor Belt is one of the biggest things in the whole solar system and by

human standards it moves with massive slowness. "Fast" in this

context means 20 to 30 miles per hour. A good bicyclist could easily keep up.

Shocking speed

The speed-up was surprising on two levels.

First, it coincided with the deepest solar

minimum in nearly 100 years, contradicting models that say a fast-moving belt

should boost sunspot production.

The basic idea is that the belt sweeps up

magnetic fields from the sun's surface and drags them down to the sun's inner

dynamo. There the fields are amplified to form the underpinnings of new

sunspots. A fast-moving belt should accelerate this process.

So where have all the sunspots been? The

solar minimum of 2008-2009 was unusually deep and now the sun appears to be on

the verge of a weak solar cycle.

Instead of boosting sunspots, Hathaway

believes that a fast-moving Conveyor Belt can instead suppress them "by

counteracting magnetic diffusion at the sun's equator."

The second surprise has to do with the bottom

of the Conveyor Belt.

SOHO can only clock the motions of the

visible top layer. The bottom is hidden by about 200,000 kilometers of

overlying plasma. Nevertheless, an estimate of its speed can be made by

tracking sunspots.

"Sunspots

are supposedly rooted to the bottom of the belt," said Hathaway. "So

the motion of sunspots tells us how fast the belt is moving down there."

He's done that — plotted sunspot speeds versus

time since 1996 — and the results don't make sense. "While the top of the

conveyor belt has been moving at record-high speed, the bottom seems to be

moving at record-low speed. Another contradiction."

Could it be that sunspots are not

rooted to the bottom of the Conveyor Belt, after all? "That's one

possibility" he noted. "Sunspots could be moving because of dynamo

waves or some other phenomenon not directly linked to the belt."

Let's go deeper

What researchers really need is a good look

deep inside the sun. NASA's Solar Dynamics Observatory, launched in February

2010, will provide that when its instruments come online later this year.

SDO is able to map the sun's interior using a

technique called helioseismology. SOHO can do the same thing, but not well

enough to trace the Great Conveyor Belt all the way around. SDO's advanced

sensors might reveal the complete circuit, which "could be the missing

piece we need to forecast the whole solar cycle," said Hathaway.

The research was published in today's issue

of Science.

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