A crack has been detected in the Earth's magnetic shield, which allowed deadly cosmic ray particles to seep through into the atmosphere.

The GRAPES-3 muon telescope, the largest and most sensitive cosmic ray monitoring system on Earth located at Tata Institute of Fundamental Research's (TIFR) Cosmic Ray Laboratory in Ooty, India, had recorded a two-hour burst of galactic cosmic rays of about 20 GeV on June 22, 2015, scientists said.

The burst happened when a giant cloud of plasma was ejected from the sun's corona and struck Earth at a speed of about 2.5 million kilometers per hour. The blast caused a severe compression of Earth's magnetosphere from 11 to 14 times the radius of the Earth. The impact triggered a strong geomagnetic storm that resulted in aurora borealis and radio signal blackouts in many high-latitude countries.

The GRAPES-3 collaboration, which includes scientists from India and Japan, performed numerical simulations and found that the Earth's magnetic shield temporarily weakened, which allowed the lower energy cosmic ray particles to enter the atmosphere.

According to the researchers, the Earth's magnetic field bent the particles about 180 degrees, from the day-side to the night-side of the Earth, where it was detected as a burst by the GRAPES-3 muon telescope. Using the 1280-core computing farm built by the GRAPES-3 team, the scientists analyzed and interpreted the data from the telescope.

"The simultaneous occurrence of the burst in all nine directions suggests its origin close to Earth," the researchers wrote in the study, which was published in Physical Review Letters. "It also indicates a transient weakening of Earth's magnetic shield, and may hold clues for a better understanding of future superstorms that could cripple modern technological infrastructure on Earth, and endanger the lives of the astronauts in space."

The magnetosphere acts as the Earth's first line of defense against the continuous flow of solar and galactic cosmic rays, protecting Earth's life forms from high-intensity energetic radiations. However, massive geomagnetic storms could reconfigure the planet's protective shield and open up weak spots that may allow the entry of radiation. Magnetized solar plasma could stretch the shield's shape at the poles and reduce its ability to repel charged particles.