Synopsis

A Crack in Earth’s Protective Shield

Physics 9, s114
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.
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.


Subject Areas

GeophysicsAstrophysics

Related Articles

An Elusive Black Hole Comes into View
Astrophysics

An Elusive Black Hole Comes into View

Observations of seven fast-moving stars at the center of a dense star cluster in the Milky Way reveal the presence of an intermediate-mass black hole, perhaps the most puzzling class of these dark objects. Read More »

Dark Matter Could Bring Black Holes Together
Astrophysics

Dark Matter Could Bring Black Holes Together

Dark matter that interacts with itself could extract significant momentum from a binary supermassive black hole system, causing the black holes to merge. Read More »

A Puzzling Excess of Cosmic Deuterons
Nuclear Physics

A Puzzling Excess of Cosmic Deuterons

A long-running experiment aboard the International Space Station has found an unexpected population of cosmic rays made of heavy hydrogen ions. Read More »

More Articles