Understanding CMEs Collisions: A Key to Protecting Earth from Future Solar Storms

Written by Dr. Shirsh Lata Soni, Postdoctoral Research Fellow at University of Michigan Ann Arbor, United States of America (USA)

As we all know, the Sun is the primary source of energy that supports life on our planet, and this energy reaches us in the form of solar radiation. In addition to this, the Sun also occasionally releases massive bursts of charged particles (mainly electrons and protons) into space, accompanied by powerful magnetic field lines. These spectacular outbursts are known as coronal mass ejections (CMEs). These energetic particles are like bullets, if they were to reach us directly, they could damage our cells, increase the risk of cancer, and even alter human and animal DNA.

Ah! Sounds terrifying, but no worries, we are shielded by the Earth’s strong intrinsic magnetic field. However, the CME can still damage the front-end electronics of a satellite and may disrupt the communication and navigation system on Earth. When a CME interacts with Earth’s magnetic field lines in a certain orientation, it can penetrate the atmosphere, where the particles collide with neutral atoms and excite them to high-energy states. These excited neutrals then emit light of various colors, creating the magnificent aurora displays in the atmosphere.

A living example was seen on May 10, 2024, when people across the Northern Hemisphere witnessed the impact of strong solar activity firsthand. where two CMEs collided along the way to Earth led to the strongest geomagnetic storm in the last 20 years, creating spectacular auroras seen over large expanses of the sky (Figure 1).

Scientists have been closely monitoring and studying CME interactions over the past few years to improve space weather forecasting capabilities. As our dependence on space-based technologies continues increasing, so does the urgency to understand how the interaction of multiple CMEs propagates into space and affects the region around the Earth. Gaining this insight is essential to help us take timely precautions and protect sensitive equipment from potential damage in advance.

A Bit More About CMEs and Why They Matter?

Coronal mass ejections are rope-like magnetic entities and plasma emanating from the outer corona of the Sun. They occur in accordance with the Sun’s 11-year activity cycle. During solar minimum, they appear approximately weekly; during solar maximum, two or three per day are emitted.

When CMEs interact, either with each other or with the solar wind, a steady flow of charged particles from the Sun, they can create larger, more chaotic structures. These interactions may enhance their effects upon arrival on Earth and may cause geomagnetic storms of sufficient power to disrupt communication networks.

As solar maximum approaches, the Sun becomes much more active, with greater amounts of solar material being expelled, and the possibility of CMEs collisions is greater. However, scientists are still attempting to determine whether CME interactions during solar maxima are more likely to cause severe space weather events (Media Ref).

The recent study led by Dr Shirsh Lata Soni at the University of Michigan, Ann Arbor, USA, observed three CMEs interacting during their journey through space using NASA’s STEREO and SOHO spacecraft. They also utilized 3-Dimensional Magnetohydrodynamics (3D-MHD) simulations of the inner heliosphere and CMEs to better understand the dynamics at play and found that CMEs involved in such interactions are twice as likely to cause geomagnetic disturbances compared to isolated events. The combination of intensified magnetic fields and elevated plasma pressure likely contributes to their enhanced Geo impact (Fig. 2). These interactions created a compressed layer of plasma and a complex magnetic structure. When this structure reached Earth, it compressed the planet’s magnetosphere, sparking an intense geomagnetic storm, the same one witnessed in early May 2024.

The May 2024 Geomagnetic Storm

Between May 8 and 9, several CMEs erupted in Earth’s direction. As they traveled outward, they merged into a larger, more complex system that struck Earth on May 10. This led to an extraordinary geomagnetic event, with the northern lights visible even from areas as far south as the southern United States.

Looking Ahead: A High-Tech Era at Risk

To monitor the evolving conditions of the heliosphere, the vast region influenced by the Sun, scientists rely on an array of observational tools. Missions like Parker Solar Probe, Solar Orbiter, and Solar Dynamics Observatory, along with ground-based facilities, provide crucial data.

These observations, combined with advanced computational models, help researchers analyze and forecast solar events in real time. By integrating data from missions such as Wind and ACE, and from networks like e-Callisto, scientists can better predict the behavior of CMEs and their potential impact.

With solar maximum peaking during 2024 and 2025, and with society more reliant than ever on satellite infrastructure for communication, navigation, and scientific research, the ability to accurately monitor and forecast solar activity is essential.

These technological and scientific advancements are key to protecting critical infrastructure and ensuring preparedness for future space weather threats.

Ref: [1] Soni, S.L., Maharana, A., Guerrero, A., Mishra, W., Poedts, S., Thampi, S., et al. 2024, Astronomy and Astrophysics, 686, A23. doi:10.1051/0004-6361/202347552.