Sun's Solar Cycle Is Governed by the Alignment of the Planets, Scientists Discover

The sun's 11-year solar cycle is governed by the alignment of the planets, with Venus, Earth and Jupiter's tidal forces influencing the solar magnetic field, scientists have found. The discovery helps explain why the sun operates on such a regular cycle—something researchers had previously struggled to account for.

The sun goes through solar cycles every 11 years, with activity peaking and waning over this period. At the height of activity—the solar maximum—more sunspots tend to appear on the sun's surface. It is also associated with more eruptions, with an increase in solar flares and coronal mass ejections—events that can have an impact on Earth. At the moment, we are in the solar minimum part of the cycle, where activity is at its lowest.

In a study published in the journal Solar Physics, researchers from the independent German research institute Helmholtz-Zentrum Dresden-Rossendorf (HZDR) say they have found evidence showing the role the planets play in the solar cycle.

The tidal forces of Venus, Earth and Jupiter produce a gravitational pull that can cause changes to the plasma on the surface of the sun. These forces are at their strongest when there is a maximum alignment of the three planets—an event that takes place once every 11.07 years.

The researchers compared observations of solar activity over the last 1,000 years with the planetary alignment—and found the two are indeed linked. "There is an astonishingly high level of concordance," Frank Stefani, lead author of the study, said in a statement. "What we see is complete parallelism with the planets over the course of 90 cycles. Everything points to a clocked process."

While the forces are too weak to change the goings on in the sun's interior directly, the researchers believe there could be an indirect mechanism resulting in the solar cycle/planet alignment they observe. They argue that a physical effect that can change the behavior of a liquid or plasma—known as the Tayler instability—could be responsible.

Sun solar flare
Image showing a solar flare on Dec. 19, 2014. NASA/SDO

The Tayler instability can react to small changes to tidal forces—with a small shift creating perturbations on the sun. Using computer models and simulations, the researchers found the momentum from the alignment from the three planets was enough to cause the changes observed. This means the planets, although through an indirect mechanism, appear to be setting the sun's solar cycles, the team concludes.

They now plan to see if other weak forces could be playing a role in the solar dynamo. By having a better understanding of what drives activity on the sun, researchers would be able to improve space weather predictions and potentially even climate-related changes on Earth—an extended period of weak solar activity in the 17th century is believed to have contributed to a mini ice age in Europe.

Scientists believe the forthcoming solar cycle—Cycle 25—will be "below average," with the next solar maximum (between 2023 and 2026) predicted to have between 95 to 130 sunspots, compared to a typical range of between 140 to 220. While low, this is still higher than the solar cycles 21 to 24.

In a statement from the NOAA, Lisa Upton, a solar physicist with Space Systems Research Corp, said: "We expect Solar Cycle 25 will be very similar to Cycle 24: another fairly weak cycle, preceded by a long, deep minimum. The expectation that Cycle 25 will be comparable in size to Cycle 24 means that the steady decline in solar cycle amplitude, seen from cycles 21-24, has come to an end and that there is no indication that we are currently approaching a Maunder-type minimum in solar activity."