Penn and Livingston have been taking a very close look at an emission line generated by a particular iron isotope. Using highly sensitive equipment at Kitt Peak McMath-Pierce telescope, this line appears to split, caused by extreme magnetism inside the spot.
This well-known phenomenon is known as "Zeeman splitting," and the amount of splitting can be used to measure the strength of the powerful magnetic field inside a sunspot.
After notching up two decades of magnetic data from using this method, the solar researchers have noticed a startling trend. The solar magnetic field strength is decreasing. Rapidly.
"This trend was seen to continue in observations of the first sunspots of the new solar Cycle 24, and extrapolating a linear fit to this trend would lead to only half the number of spots in Cycle 24 compared to Cycle 23, and imply virtually no sunspots in Cycle 25," Penn and Livingston say in their paper submitted to the International Astronomical Union Symposium No. 273 (emphasis added).
Since they started taking results, the researchers have noticed an average magnetic field strength decrease of 50 Gauss per year (as a comparison, the Earth's magnetic field barely measures in at 1 Gauss).
"...we assume that the magnetic threshold of 1500 Gauss represents a real physical limit for the formation of a dark spot (either a pore or a sunspot) on the solar photosphere," they add.
If the decreasing trend continues its downward slope, by 2016, the average sunspot magnetic field has the potential to be below this 1500 Gauss threshold, leading to the possibility that the sun will generate no sunspots.
The last time this happened in documented history was in the 17th and 18th century when the sun didn't produce any sunspots for decades. This extended period of calm, known as the Maunder Minimum, coincided with an extended period of cooling on Earth, a period called the Little Ice Age.
Are we witnessing another slow-down in solar magnetic activity? Could this be a part of a long-period cycle where the sun runs out of juice and forgets to produce sunspots every few hundred years?
I've been following Penn and Livingston's research for some time, and it is fascinating to say the least. Although they are the first to admit their work is far from conclusive - two decades-worth of solar data isn't a lot after all - this downward trend in magnetic field strength is a conundrum.
Although the sun is our nearest star, it certainly isn't ready to give away many clues as to how it works quite yet.