Echoes of Solar Fury - Solar Storms in Earth’s Memory

From time to time, meteorologists alert us during news broadcasts about rare solar storms, which may include jet eruptions. They often reassure us that these phenomena are distant from Earth. However, there is no safe haven: some solar storms are of such magnitude that trees and water bear their marks for years and even ages.

Some of these exceptional events are known as "Miyake events," named after the young Japanese physicist Fusa Miyake, who defined them scientifically not long ago, in 2012, at the end of her doctoral studies. If such an event were to occur today, it could have severe consequences for our communication systems, affecting everything from smartphones to satellites.

Some solar storms are so powerful that trees and water bear their marks for years and ages. Image of a solar storm | NASA/Goddard Space Flight Center

Particle Barrage

How do Miyake events differ from other solar storms? Primarily in their intensity and impact on Earth. A typical solar storm, or a Solar Particle Event (SPE) in scientific terminology, is characterized by the emission of charged particles, typically protons or helium nuclei. Accelerated to very high speeds by the solar atmosphere, these particles travel toward planets. Occasionally, these storms affect satellites beyond Earth's atmosphere, with the particle flux hitting the satellites and causing communication disruptions.

Periodically, a more significant event occurs, leading to an elevated presence of specific particles on Earth's surface: Carbon-14, a radioactive carbon isotope, which is a carbon atom with six protons and eight neutrons in its nucleus, and Beryllium-10, an isotope of beryllium, which is a beryllium atom containing four protons and six neutrons.

Both these isotopes are exceedingly rare on Earth. Normally, out of a trillion carbon atoms, only one atom is Carbon-14 and, as far as we know, Beryllium-10 is even scarcer. It is found on Earth in such minuscule quantities that we can detect its presence and know of its existence solely through its decay products.

During every solar event, these two isotopes are generated in Earth's atmosphere when neutrons arriving from the sun collide with light nuclei of gasses in the atmosphere, such as nitrogen. The resulting isotopes are among the products of these reactions

Occasionally, a more significant event occurs, leading to an increase in the presence of certain particles on the ground. Illustration of particles from a solar storm reaching Earth | NASA

A Happy Isotope 

After having formed in the atmosphere, these isotopes make their way to the ground. Trees incorporate the isotope Carbon-14 during photosynthesis, while Beryllium-10 accumulates in ice, eventually reaching the ground through precipitation. Thus, even many years after a Miyake event, analysis can be conducted to understand its occurrence and timing. Carbon-14 imprints in trees provide a well-established dating method in archaeology, using the isotope's half-life, which is the time it takes for half of the original amount of the substance to decay. Tree rings, as we learned in childhood, also help determine the age of the tree; this method is called dendrochronology, derived from the Greek word for tree, "dendron."

One such example can be found in the Druzet River area in the southern French Alps. Researchers recently examined Carbon-14 samples from 172 trees there, and carbon dating led to the conclusion that a Miyake event impacted the area around 14,300 years ago, towards the end of the last ice age. Additional and independent verification for this came from as far as Greenland’s ice cores, which contained traces of Beryllium-10. The match was complete, and according to the researchers, this event represents the oldest and most significant Miyake event known. During the decade that has passed since Miyake's paper describing them was published, six such events were identified over approximately 8,000 years.

While those who lived then may have seen signs of this event in an aurora that ovccured near the equator, similar to the northern and southern auroras, there is no evidence of this. Apart from that, the event had no impact on humans. Today, Miyake says, the situation is completely different: a similar event would severely disrupt modern data communications – satellites, radio, telephone, telegraph, and more – even if temporarily.

Trees preserve evidence of a Miyake event in this area dating back 14,300 years. Fossil tree in the Druzet River area | Cécile Miramont