When solar activity reached an all-time low in 2008, astronomers reasonably figured the Sun was entering into a period of historically low activity. They were wrong.
New research published September 8 in The Astrophysical Journal Letters suggests that 2008 marked the beginning of a steady increase in solar activity. To be clear, this “reversal” extends beyond the well-known 11-year cycles the Sun typically follows. Specifically, the researchers found a slow uptick in many of the Sun’s key “vitals,” such as solar wind frequency and the strength of the magnetic field, since 2008.
“All signs were pointing to the Sun going into a prolonged phase of low activity,” said Jamie Jasinski, study lead author and a NASA researcher at the Jet Propulsion Laboratory, in a statement. “So it was a surprise to see that trend reversed. The Sun is slowly waking up.”
Reading the solar signs
The solar cycle—an approximately 11-year interval marked by the rise and fall of sunspot numbers—is a well-documented phenomenon. The Sun’s magnetic field flips polarity every 11 years, returning to its original state after completing two full solar cycles. This 22-year magnetic phase is known as the Hale cycle.
Of course, like many other astrophysical patterns, this rule has some exceptions that scientists have yet to fully understand. Multiple historical records present clear evidence of long periods of unusually low solar activity that lasted 30 to 40 years, Jasinski said.
These trends are a lot harder to predict, Jasinski added. But data since the 1980s did really appear to imply that the Sun was “heading toward a historic lull,” according to the researchers. However, a closer scrutiny of solar activity after 2008—when solar activity reached an unprecedented low—revealed a clear reversal of the weakening trend.
After 2008 the “trend of declining solar wind ended,” Jasinski explained. “Since then plasma and magnetic field parameters have steadily been increasing.”
The researchers’ analysis shows that the Sun is likely “recovering” from a 20-year decline in solar activity. Between 2008 and 2025, key solar wind indicators—including speed (~6%), density (~26%), temperature (~29%), and thermal pressure (~45%), among other metrics—have steadily increased. This suggests that the recent period of unusually weak solar activity may have been an “outlier” in the broader, long-term solar trend, according to the paper.
Solar activity and space weather
The Sun lies at the center of our solar system. Whenever the star spits out radiation bursts or plasma bubbles, the planets feel the heat—literally. Strong solar activity can compress the protective magnetic shield surrounding each planet, including Earth.
This makes Earth a lot more vulnerable to the brutal radiation and plasma jets coming from the Sun. When that happens, solar weather can wreck satellite networks and electrical grids on Earth. For space missions, directly encountering solar weather events could be detrimental to the health of both astronauts and the spacecraft, giving NASA an imperative to better understand the nature of these events.
Technological advances enable scientists to capture solar activity in better detail than ever before. Still, the new paper suggests that a second look is always worth a try when dealing with the fickle, elusive behavior of our host star. In the paper, the authors noted that the “continuing [16-year] increase in the solar wind dynamic pressure will have consequences” in the solar environment.
This upward trend has already passed the 11-year mark, suggesting that the Sun is currently in one of those uncommon, extended cycles. When and how this will end isn’t clear, the researchers said.
“The longer-term trends are a lot less predictable and are something we don’t completely understand yet,” Jasinski added.