New Maunder Minimum?

At the annual meeting of the Solar Physics division of the American Astronomical Society, Frank Hill, Matt Penn, William Livingston, Richard Altrock and collaborators presented data indicating that the Sun may be heading that direction after Solar Cycle 24 is complete. So what does this mean?

Well first lets go over what the Maunder Minimum was. Humans have been observing sunspots regularly since Galileo first turned his telescope towards the Sun. (WARNING: DO NOT DO THIS UNLESS YOU HAVE A SOLAR FILTER FOR YOUR TELESCOPE!!!) Since that time a record has been kept of the number of sunspots on the Sun. This one of the longest scientific observing records to date, with over 400 years of data. It was discovered that the number of sunspots rises and falls over a period of 11 years. However, something strange happened to this pattern between 1645 and 1715, known as the Maunder Minimum. During this time the Sun showed few if any sunspots.

Since that time heliophysicists have discovered the cause of sunspots and the sunspot cycle. Sunspots are caused by regions of intense magnetic field on the Sun. This magnetic field keeps the region of the sunspot cooler than the surrounding plasma, thus the sunspot looks dark. The cycle of the sunspots is related to the cycle over which the magnetic field on the Sun reconfigures. Every 11 years, the magnetic field of the Sun flips its direction so that the North pole becomes the South and visa versa. During a minimum in Solar activity the magnetic field is stable in its orientation. However, as solar activity increases, indicated via the proxy of an increasing sunspot number, the magnetic field becomes chaotic as it flips direction. This chaotic field is the seed for the solar activity. Thus the Sun flips its magnetic field every 11 years, leading to the 11 year sunspot cycle.

Helioseismologists have recently uncovered more detail about this process. It all relates to the different flows with in the Sun's convection zone. In this region, particularly the region known as the tachocline, the magnetic field for the Sun is thought to be generated. Scientists have discovered large scale flows which control the motion of sunspots on the Sun. They have also discovered jet streams, similar to the ones found on Earth, which can be used to predict when new sunspot cycles begin. This was used to predict the late onset of the current sunspot cycle labelled Cycle 24.

Current data from Frank Hill's group shows that the jet streams for Cycle 25, the next cycle, have not formed yet which is unusual. If they don't form at all Cycle 25 probably won't happen. Penn and Livingston presented data that indicated that the sunspots have been weakening over the past 2 cycles. Altrock presented data showing that the field accumulation at the poles of the Sun has slowed as well. The combined data indicates that Cycle 25 will either be weak or not occur at all. If Cycle 25 doesn't happen it may be the start of another Maunder Minimum (aka grand minimum).

So what would be the implications for us here on Earth if another Maunder Minimum were to occur? Well there would be less activity from the Sun. A lower number of solar flares and Coronal Mass Ejections. This would lead to lower auroral activity. It would also make it safer for people out in space as the chances of being exposed to harmful radiation from the Sun would decrease. It would also lower the danger activity from the Sun poses to electronics in space and on Earth. The Sun would also put out less radiation making it slightly cooler here on Earth. In fact the Maunder Minimum coincided with the middle Little Ice Age in the 17th century. While the minimum certainly contributed to the Little Ice Age, the main cause was vulcanism here on Earth, so don't expect the cooler Sun from a minimum to counter act global warming. In fact the Sun would have to get 10 times cooler than it would become during a grand minimum to make up for the net effect of greenhouse emissions, so no worries of a new Ice Age yet.

A grand minimum would also be extremely interesting to heliophysicists. This is because we don't know what caused the original Maunder Minimum. Also while we have a pretty good idea about how the magnetic field on the Sun works, we still know very little about its generation. Observing another grand minimum would help us to understand both of these topics.

So will the Sun go into another grand minimum or not? Only time will tell if the predictions from the recent data hold true. As more data is accumulated better models will be generated and we will get a better idea of how Cycle 25 will likely play out. Ultimately, as with weather forecasting, you will never know for sure until you get to the actual date of the event to see if it happens.