The magnetic field that protects Earth from deadly cosmic radiation may be more vulnerable than previously thought. A crack in the shield caused by a solar flare which exposed the planet to a bombardment of radiation has been detected.

Researchers from the Tata Institute of Fundamental Research in India made the discovery when analyzing a galactic cosmic ray burst that caused radio blackouts across North and South America and a supercharged aurora borealis in 2015.

The cosmic ray source was a giant solar plasma cloud that travelled 40 hours from our sun to reach Earth, where the researchers believe it caused a transient “weakening of Earth’s magnetic shield”, according to their findings published in the journal Physical Review Letters.

The sun’s flare was so intense the team claim it would have shrunk the magnetic field from 11 times the radius of Earth to four times its radius before it eased, allowing the shield to recover.

Researchers used data from the GRAPES-3 muon telescope in Ooty, India, to simulate the burst. Results indicated the effect on Earth would have required a crack in the magnetic field that lasted approximately two hours.

Unfortunately not a lot can be done to protect Earth from any future cracks in the shield, which could leave the planet under constant exposure to radiation and could potentially lead to the eradication of our atmosphere.

The team were optimistic the knowledge gained would have positive results though, claiming it could “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.”

Astronauts onboard the International Space Station (ISS) fall within the field’s 56,000km extension around Earth but future voyagers to Mars would likely be exposed to the rays for long periods.

Transient Weakening of Earth’s Magnetic Shield Probed by a Cosmic Ray Burst

The GRAPES-3 tracking muon telescope in Ooty, India measures muon intensity at high cutoff rigidities (15–24 GV) along nine independent directions covering 2.3 sr. The arrival of a coronal mass ejection on 22 June 2015 18:40 UT had triggered a severe G4-class geomagnetic storm (storm). Starting 19:00 UT, the GRAPES-3 muon telescope recorded a 2 h high-energy (∼20  GeV) burst of galactic cosmic rays (GCRs) that was strongly correlated with a 40 nT surge in the interplanetary magnetic field (IMF). Simulations have shown that a large (17×) compression of the IMF to 680 nT, followed by reconnection with the geomagnetic field (GMF) leading to lower cutoff rigidities could generate this burst. Here, 680 nT represents a short-term change in GMF around Earth, averaged over 7 times its volume. The GCRs, due to lowering of cutoff rigidities, were deflected from Earth’s day side by ∼210° in longitude, offering a natural explanation of its night-time detection by the GRAPES-3. The simultaneous occurrence of the burst in all nine directions suggests its origin close to Earth. 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.

Figure 1
Top 3 panels show WIND data time shifted to the bow-shock nose: (a) VSW, (b) |B|, (c) Bz, (d) GRAPES-3 muon-rate. Vertical dashed lines indicate CME arrival times (UT).
Figure 2
Muon-rate (solid line) and −Bz (broken line) on 22 June 2015, correlation coefficient R=−0.94.

Figure 3
Muon-rate variation in nine directions observed by GRAPES-3 on 22 June 2015 shown by the solid line. Simulation results normalized to data by scaling the IMF 17 times are shown by the broken line. Cutoff rigidities (GV) and error bars are shown for each direction

Figure 4
GCR trajectories near the cutoff rigidity responsible for the burst viewed from the (a) north pole and (b) the equator. NW, N, NE shown in blue, W, V, E in green, SW, S, SE in red.