A sun with no sun spots? What that could mean for Earth and its climate.
Three studies suggest a decline in sun spots – to the point that they could largely vanish for a long period. That could lead to fewer solar storms, as well as a chance to study whether fewer sun spots leads to a cooler climate on Earth.
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Drawing on 13 years of sun-spot data, National Solar Observatory researchers Matt Penn and William Livingston have documented a consistent decline in the strength of the magnetic fields associated with sun spots. If the strength of those fields drops below a certain level, the spots vanish.Skip to next paragraph
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If the decline in magnetic-field strength continues at its current pace, Dr. Penn says, the current solar cycle, Cycle 24, will be half a strong as the last one.
"Cycle 25 may have no sun spots at all," he adds.
Hill's group at the National Solar Observatory used measurements of the sun's acoustic signals to gauge the movement of high-speed jet streams of solar material inside the sun's northern and southern hemisphere. These jet streams tend to form at high latitudes and migrate toward the equator over the course of a sun-spot cycle. And they tend to be the spawning grounds for sun spots.
Typically, new jets, the foundations for a new sun-spot maximum, form even before the existing jets reach the equator and vanish, Hill explains. The new jets should have started forming in 2008. They have yet to appear.
A rush to the poles
Finally, a team led by Richard Altrock, who heads the US Air Force's corona research program, used 40 years of data to track how magnetic structures in the sun's corona – its outer atmosphere – "rush to the poles" on the sun toward the end of a solar cycle.
This "rush" typically starts at around 70 degrees latitude on the sun at the start of a solar cycle, with the new magnetic structures forcing the leftovers of the old cycle to migrate toward the sun's poles.
The current solar cycle saw this migration begin late and take place slowly, suggesting the new fields may not be strong enough to keep the old ones moving. Indeed, the older structures themselves for this cycle look weaker than their predecessors.
Hill notes that the weakening may provide further evidence of an 80- to 90-year sun-spot cycle, in which the 11-year cycle is embedded.
One of these "grand minima" occurred between 1460 and 1550, while another appeared between 1790 and 1830. Given the margins of error in those time estimates, if the sun's slowdown continues, it could be the latest in a line of these grand minima, during which solar activity drops dramatically, even at the peaks of the solar cycle, but sun spots still appear.
Whatever happens, "it's more information that can be used by people who do the theory of how this all works," Hill says.
Researchers have much yet to learn about how the sun works – the basis for understanding stars in general.
Theorists "have not really touched the problem of grand minima yet," Hill adds.