Sunspots could be set to disappear altogether after the next solar maximum, new studies indicate.
Right now, the sun is in the middle of Cycle 24, and is due to reach a maximum in 2013. The next cycle would be expected to start in around 2020.
But separate examinations of the sun's interior, surface and upper atmosphere all indicate that the next cycle will be significantly weakened.
Indeed, we may be heading into what's known as a 'grand minimum' - a period of unusually low solar activity. The last such, known as the Maunder Minimum, took place between 1645 and 1755. Almost no sunspots were observed during this time.
The studies drew their conclusions from a missing jet stream in the interior of the sun, vanishing sunspots on its surface and changes in the corona and near the poles.
The National Solar Observatory (NSO) says that, based on 13 years of observations, sunspots are weakening. There have been fewer during the present cycle - and, if the trend continues, there may be none at all in the next.
Meanwhile, NSO observations of the jet streams circling the sun, whose strength tends to correlate with solar activity, has shown that activity is near-non-existent. Were the next solar cycle to proceed as usual, they would have appeared two or three years ago.
Finally, the sun's corona, or upper atmosphere, is also failing to show changes associated with the usual solar cycles. Normally, scientists would expect to see magnetic features in the corona moving north and south in a phenomenon known as the rush to the poles. This time, however, they're moving at a crawl.
"This is highly unusual and unexpected," Frank Hill, associate director of the National Solar Observatory's Solar Synoptic Network, told Space.com.
"But the fact that three completely different views of the sun point in the same direction is a powerful indicator that the sunspot cycle may be going into hibernation."
The Maunder Minimum coincided with what's known as the Little Ice Age, a period of unusual cold. But the scientists say there doesn't appear to be a link between solar activity and the earth's climate, with the Little Ice Age having been triggered by volcanic eruptions.