Alignment Of Planets May Explain Sun's Mysterious Cycle

Magnetic map of the Sun by SDO. NASA/SDO/AIA/LMSAL

The Sun's magnetic field influences many different Earthly phenomena, but we are not exactly sure how it works. Now, a new theoretical study suggests a planetary alignment could play a crucial role in it.

Researchers from the Helmholtz-Zentrum Dresden-Rossendorf Association in Germany have looked at the potential influence that planets might have on the Sun. In their simulation, the team discovered that when Venus, Jupiter, and Earth are aligned, they produce a small but significant force on the Sun that leads to complex changes in its magnetic field.

We can imagine the Sun as an enormous dynamo. Stars are made of hot charged particles, the stellar plasma, and as they rotate on themselves these particles generate an intense magnetic field. The solar dynamo is influenced by the interior structures of the Sun, and it is responsible for the famous sunspots, dark patches on the surface of the Sun. The dynamo’s polarity reverses with an 11-year cycle, which made scientists very curious.

"Interestingly, every 11.07 years, the Sun and the planets Venus, Earth, and Jupiter are aligned," lead author Dr Frank Stefani said in a statement. "We asked ourselves: Is it a coincidence that the solar cycle corresponds with the cycle of the conjunction or the opposition of the three planets?"

Many researchers had previously suggested the planets may play a role in the solar cycle. This study though, published in Solar Physics, didn’t look at the observational validity of this idea but at the purely theoretical setup.

The researchers found that it is indeed the case. Although the combined effect of the planets is small, they create a resonance in one of the Sun’s magnetic features known as the alpha effect, which is responsible for, among other things, sunspots.

According to the study, when the planets are aligned their gravity combines to cause a tidal-like effect on the Sun's plasma, pulling it and disrupting the Sun's magnetic field. This may be enough to effect the whole dynamo effect on the Sun, possibly playing a part in its cycles.

The alignment is a neat explanation for the timing of the solar cycle, but since it is based exclusively on theoretical considerations it is not a full explanation for the complex magnetism of our star. The rotation and gravity of the Sun, and the energy and particles emitted, are some of the many factors that can affect the solar dynamo. 

Although the solar cycle is fairly regular, there are indications of longer secular effects that might come into play and a gravitational explanation might not be sufficient. The finding is nevertheless very interesting, and the next step will be to look for more evidence supporting this fascinating hypothesis. 

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