If the Sun goes spotless in decades to come, as some scientists are predicting it might, what does it mean for Earth? Scientists are studying the past to predict the future of space weather.
In 1645, the sun became nearly spotless. During the 70-year period that followed, known as the Maunder Minimum, sunspots appeared only rarely on the surface of the Sun. Now, after a peak in magnetic activity that drove the appearance of a multitude of sunspots during the 1950s and 60s, the Sun again appears to be headed toward such a minimum.
Yet it's not always a bad thing when history repeats itself — it means that we can study the past to predict the future. And that’s just what scientists such as Mathew Owens (University of Reading, UK) are doing. In Nature's January 31st Scientific Reports, Owens and colleagues look back to the Maunder Minimum in order to anticipate solar and auroral activity (or the lack thereof) in our near future.
Then and Now
The Maunder Minimum* was named after solar astronomers Annie Russell Maunder and E. Walter Maunder who first discovered the extended period of abnormally low sunspot reports. During this time, the Sun continued its 11-year cycle of activity, with its sunspot count rising to maximum and falling to minimum again. However, even with Giovanni Cassini, Johannes Hevelius, and several others regularly observing the Sun, only a couple dozen sunspots were recorded over a 70-year timespan.
And in recent years, it has become apparent that the modern era seems to be headed toward a minimum of sorts, too. The current cycle of solar activity, known as Cycle 24, peaked in 2013, but the peak was the weakest recorded in 100 years. And although solar cycle predictions is a risky business (many predictions for Cycle 24 were flat-out wrong), many experts anticipate that Cycle 25 will be weaker still. If the trend continues, we could be looking at a largely blank Sun in the next few years — another Maunder Minimum.
“I'd say at this point that a Maunder Minimum in the next 50 years is probably ‘more likely than not,’” says Owens, though he cautions against predicting activity in an individual cycle.
The difference between the current weak cycles and the Maunder Minimum consists of rocket science, literally: The Space Age has long since changed the ball game for solar science, enabling scientists to garner data on everything from the solar wind speed and density at Earth to detailed views of the Sun’s magnetic field.
All we have from the Maunder years, on the other hand, are sunspot counts — tiny dots that give only a narrow view into the Sun’s inner workings.
Study the Past, Predict the Future
So that’s why Owens and colleagues replayed the past 30 years of solar activity on a computational model of the Sun’s magnetic field, using modern data to guide the model. They compared the model’s output to sunspot counts, comparing the number of sunspots to properties of the Sun’s magnetic field such as the speed of the solar wind it produces.
With this accomplished, Owens’ team then took the model back in time, retracing the Maunder Minimum. With only the sparse sunspots as input, the model postdicted what the Sun and the solar wind would have looked like, basically reconstructing the space weather of 400 years ago.
“Much work has been done to try to understand deep minima for the Sun and other stars,” says Tom Schad (DKIST), who was not involved in the study. “The strength of [this] work lies in the advanced nature of the magnetohydrodynamic models themselves.”
Of course, extrapolating a model so far back in time runs the risk of no longer being relevant, Schad adds. “Multiple approaches to the investigation of deep minimum are paramount.”
So what does all of this mean for our future, if that future really includes a deep minimum? Fewer sunspots, a weaker solar wind, and overall reduced magnetic activity point to a future with fewer Northern Lights — and those auroras that do appear will concentrate more around the poles than they do right now.
But don’t lose all hope! Earth’s magnetic pole, Owens says, is moving away from the UK and in the direction of the U.S. “The loss of aurora situation for the US may not be as severe as the UK!”
*Coincidentally, the Maunder Minimum appeared at the middle of the Little Ice Age, leading some to suppose a connection between sunspots and weather, but given that the Maunder Minimum began 50 years after the Little Ice Age started, the two are likely unrelated.