On the other hand, he offers, scientists may merely be watching another cycle with a delayed onset, similar to the run-up to the current sun-spot cycle, which started more than a year late.
Sun spots are relatively cool regions of hot gas on the sun's surface, prevented by intense magnetic fields from plunging back into the depths of the sun for a reheat. These spots wax and wane in a cycle that averages 11 years.
During the peak of the cycle, the sun is at its most active, generating flares, prominences, and unleashing the granddaddies of solar outbursts: coronal mass ejections (CMEs).
All of these can occur at any time during the solar cycle, but they are most frequent during its peak.
Last week, for instance, the sun unleashed an enormous mass of charged particles in a coronal mass ejection that struck Earth a glancing blow. still, it triggered auroral displays closer to the equator than usual and anxious moments for utility-grid and satellite operators.
Evidence for a potential long-term slowdown or even halt to sun spots for a period come through three sets of measurements.
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.
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.