Science & Environment

Scientists record breach in magnetic field

Earth's magnetosphere Image copyright Science Photo Library
Image caption Artwork: The Earth's magnetosphere protects the planet from a continuous flow of cosmic radiation

Scientists have recorded the events that unfolded after the Earth's magnetic shield was breached.

Openings in the planet's magnetic field are not uncommon, but it is rarer to get the opportunity to gather data while such an event is in progress.

A cosmic ray monitoring facility recorded a burst of cosmic rays associated with the opening.

The magnetic field breach was the result of charged particles from the Sun striking the Earth at high speed.

The GRAPES-3 muon telescope located at the Cosmic Ray Laboratory (CRL) in Ooty, southern India, recorded a burst of galactic cosmic rays of about 20 gigaelectronvolts (GeV) on 22 June 2015.

Image copyright TIFR
Image caption The opening in the magnetic shield was detected with the GRAPES-3 muon telescope

"In this case the magnetic field was breached for only two hours and then returned back to normal. The magnetic field strength reduced only by 2%," Dr Sunil Gupta, lead scientist at the CRL told the BBC.

Earth's magnetic shield, or magnetosphere, extends over a radius of a million kilometres. It protects the planet's biosphere from the continuous flow of solar and other cosmic radiation.

The Sun periodically ejects vast clouds of charged particles into space in events known as coronal mass ejections (CMEs). Each one can contain a billion tonnes of charged gas, or plasma.

The giant cloud of plasma ejected from the solar corona in 2015 caused massive compression of the Earth's magnetosphere and triggered a severe geomagnetic storm. In turn, this generated aurora borealis (northern lights), and radio signal blackouts in many high latitude countries.

Image copyright NASA/SDO/AIA
Image caption The Sun periodically ejects vast clouds of charged particles into space

Numerical simulations performed by the GRAPES-3 team on this event indicate that the Earth's magnetic shield temporarily opened up in response to the incoming solar plasma, allowing the lower energy galactic cosmic ray particles to enter our atmosphere.

Dr Gupta said that the CRL's measurements of the two-hour breach "gives us much more comprehensive information over a much larger region of space than the satellite based instruments".

The GRAPES-3 Muon telescope's combination of a large area and directional measurement enabled the accidental observations.

Image copyright DR P. MARAZZI/SCIENCE PHOTO LIBRARY
Image caption Auroras are one of the consequences of geomagnetic storms

"We have been aware of impacts on the Earth from solar activity for a long time through the discovery of CMEs, but the Indian study adds a new element to this endeavour, with detailed analysis of a major particle event during the arrival of a particular cloud," Dr Richard Harrison, head of space physics and chief scientist at the Rutherford Appleton Laboratory in Oxfordshire, UK, told BBC News.

A major event could occur any time with potentially significant impacts on human infrastructure. As such, there are ongoing efforts to improve the prediction of this so-called space weather.

"They can short circuit power supplies such as high voltage transformers which provide power to our cities, disrupt communication satellites and therefore will affect, for example, internet, mobile phones and just about anything that uses electricity," said Dr Harrison.

In addition, he said, a major solar storm could also threaten humans in space, with the potential for damage to or the loss of spacecraft - although such events are expected to be rare.

Scientists at CRL hope that the vast amount of data now available would enable them to better predict such events and take preventative measures. But the real challenge is to devise appropriate electronic hardware that can issue a reliable alert, Dr Gupta said.

The findings have been published in the journal Physical Review Letters.