Synopsis: A Crack in Earth’s Protective Shield

Observations with India’s cosmic-ray telescope indicate that Earth’s magnetic field weakened during a 2015 geomagnetic storm, allowing cosmic rays to pass through.
Synopsis figure
S. K. Gupta/Tata Institute of Fundamental Research

In the early hours of June 21, 2015, a giant cloud of magnetized plasma was ejected from the Sun in a solar flare. Forty hours later, those particles slammed into Earth’s magnetosphere, triggering a severe geomagnetic storm that knocked out radio signals in North and South America. New observational data from the GRAPES-3 cosmic-ray telescope in India show that an unusually high flux of cosmic rays breached the magnetosphere during this storm, resulting in a 2-hour-long cosmic-ray shower on Earth. Simulations performed by the GRAPES-3 collaboration, which includes researchers from India and Japan, suggest that the burst of cosmic rays was allowed to enter because the geomagnetic storm temporarily weakened Earth’s polar magnetic field.

Earth’s magnetic field deflects most cosmic rays, protecting living things from harmful radiation. But large geomagnetic storms can reconfigure this protective shield, opening up weak spots that let radiation and cosmic rays slip through. This vulnerability can occur when magnetized plasma from the Sun deforms Earth’s magnetic field, stretching its shape at the poles and diminishing its ability to deflect charged particles. Numerical simulations performed by the GRAPES-3 researchers suggest that this is exactly what happened following the June 21 solar flare, allowing the cosmic-ray breach that their telescope detected.

This research is published in Physical Review Letters.

–Katherine Wright

Katherine Wright is a Contributing Editor for Physics.


More Features »


More Announcements »

Subject Areas


Previous Synopsis

Next Synopsis

Semiconductor Physics

Valley of the Dichalcogenides

Read More »

Related Articles

Viewpoint: Neutron Star Merger Seen and Heard

Viewpoint: Neutron Star Merger Seen and Heard

For the first time, researchers have detected both light and gravitational waves from the same event in space. Read More »

Focus: Drops Falling in Clouds Make More Drops
Fluid Dynamics

Focus: Drops Falling in Clouds Make More Drops

Experiments with a simplified version of the atmosphere show that falling drops seed many smaller droplets in their wake. Read More »

Synopsis: Self-Interacting Dark Matter Scores Again

Synopsis: Self-Interacting Dark Matter Scores Again

Dark matter that interacts with itself provides a better description of the speeds of stars in galaxies than dark matter that doesn’t self-interact. Read More »

More Articles