The remarkable auroras observed in early May have demonstrated the potential power that solar storms can unleash in the form of radiation. However, sometimes the Sun can be far more destructive. Known as “solar particle events,” these streams of protons can shoot out from the Sun’s surface like headlights into space.
Records indicate that approximately every thousand years, Earth is subjected to an extremely powerful solar particle event, which can cause significant damage to the ozone layer and increase ultraviolet (UV) radiation levels at the surface. During periods when Earth’s magnetic field is weak, these events can have profound effects on life across the planet.
The Earth’s Essential Magnetic Shield
The Earth’s magnetic field provides a crucial protective cocoon for life, deflecting charged radiation from the Sun. In its normal state, it functions like a giant magnet, with magnetic field lines emanating from one pole, circling around, and plunging down at the other pole. The vertical orientation at the poles allows some ionizing cosmic radiation to penetrate down to the upper atmosphere, where it interacts with gas molecules to produce the light we call auroras.
The Earth’s magnetic field (in blue) acts as a shield against solar wind composed of particles from the Sun (in orange). (Photo: Koya 979).
However, the magnetic field changes significantly over time. In the past century, the North Magnetic Pole has moved across northern Canada at a rate of about 40 kilometers per year, and the magnetic field has weakened by over 6%. Geological records indicate that there have been periods lasting centuries or even millennia when the geomagnetic field was very weak or even entirely absent.
What would happen without Earth’s magnetic field, similar to Mars, which lost its global magnetic field in ancient times, along with much of its atmosphere? In May, shortly after the auroras, a strong solar particle event struck Mars. It disrupted operations of the Mars Odyssey spacecraft and increased radiation levels on the Martian surface to about 30 times normal.
The Power of Protons
The outer atmosphere of the Sun emits a continuous flow of electrons and protons known as “solar wind.” However, the Sun’s surface also occasionally releases energy streams, primarily protons, during solar particle events—often associated with solar flares.
Protons are much heavier than electrons and carry significantly more energy, allowing them to reach lower altitudes in Earth’s atmosphere, where they excite air molecules. However, these excited molecules only emit X-rays, which are invisible to the naked eye.
Hundreds of weak solar particle events occur during each solar cycle (approximately 11 years), but scientists have found evidence of many stronger events throughout Earth’s history.
Extreme Solar Particle Events
Extreme solar particle events happen roughly every few millennia. The most recent event occurred around the year 993 AD and has been used to demonstrate that Viking structures in Canada were made from timber cut in 1021 AD.
Less Ozone, More Radiation
In addition to their immediate effects, solar particle events can trigger a chain reaction in the upper atmosphere that can deplete the ozone layer. Ozone absorbs harmful UV radiation from the Sun, which can damage eyesight and DNA (increasing the risk of skin cancer), as well as affect the climate.
In a recent study, scientists used large computer models of global atmospheric chemistry to examine the effects of an extreme solar particle event. They found that such an event could decrease ozone levels for about a year, increase UV radiation on the surface, and heighten DNA damage. However, if a solar proton event occurs during a time of very weak Earth’s magnetic field, ozone damage could last six years, increasing UV radiation levels by 25% and raising solar-induced DNA damage rates by up to 50%.
Particle Outbursts from the Past
The most recent period of weak magnetic field—including a temporary shift in the North and South Poles—began about 42,000 years ago and lasted roughly 1,000 years. Several significant evolutionary events occurred around this time, such as the disappearance of the last Neanderthals in Europe and the extinction of large marsupials, including the Diprotodon and kangaroos in Australia.
Similarly, the rapid evolution of diverse animal groups during the Cambrian Explosion (approximately 539 million years ago) is also linked to geomagnetism and high UV levels.
