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GRAPES-3 indicates a crack in Earth's magnetic shield

Inside a muon telescope building

Inside a muon telescope building

The GRAPES-3 experiment located at the Cosmic Ray Laboratory (CRL) in Ooty consists of two major components, first an array of 400 plastic scintillator detectors, and second a large area muon telescope. The GRAPES-3 led by Prof. Sunil K.Gupta, has participation of about 30 scientists from 7 universities in India, and from 5 in Japan.

The GRAPES-3 muon telescope recorded a burst of galactic cosmic rays of about 20 GeV, on 22 June 2015 lasting for two hours.

The burst occurred when a giant cloud of plasma ejected from the solar corona, and moving with a speed of about 2.5 million kilometers per hour struck our planet, causing a severe compression of Earth’s magnetosphere from 11 to 4 times the radius of Earth. It triggered a severe geomagnetic storm that generated aurora borealis, and radio signal blackouts in many high latitude countries.

Earth's magnetosphere extends over a radius of a million kilometers, which acts as the first line of defence, shielding us from the continuous flow of solar and galactic cosmic rays, thus protecting life on our planet from these high intensity energetic radiations.

Numerical simulations performed by the GRAPES-3 collaboration on this event indicate that the Earth's magnetic shield temporarily cracked due to the occurrence of magnetic reconnection, allowing the lower energy galactic cosmic ray particles to enter our atmosphere. Earth's magnetic field bent these particles about 180 degree, from the day-side to the night-side of the Earth where it was detected as a burst by the GRAPES-3 muon telescope around mid-night on 22 June 2015. The data were analyzed and interpreted through extensive simulation over several weeks by using the 1280-core computing farm that was built in-house by the GRAPES-3 team of physicists and engineers at the CRL, Ooty. In fact, all detector systems, and signal processing electronics were designed, and made in the CRL, Ooty ensuring prompt repair in cases of equipment failure, thus enabling uninterrupted operation since 2000 leading to the detection of this burst.

This work has recently been published in Physical Review Letters (doi:

Solar storms can cause major disruption to human civilization by crippling large electrical power grids, global positioning systems (GPS), satellite operations and communications. The United States President, Barack Obama, has recently issued an executive order to prepare and protect the country from such disasters triggered by extreme solar storms.

The GRAPES-3 muon telescope, the largest and the most sensitive cosmic ray monitor operating on Earth is playing a very significant role in the study of such events. This finding has generated widespread excitement in the international scientific community, as well as electronic and print media.

Links to articles

Research paper: P. K. Mohanty et al., Phys. Rev. Lett. 117, 171101 (2016),  


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Dr Pravata K  Mohanty,  Email: