How Earth is protected from space weather

Scientists have shown that in certain circumstances a pool of dense particles normally circling Earth, deep inside the magnetosphere, can extend a long arm out to meet - and help block - incoming solar material.

Brian Walsh, a space scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, said that the material that is usually much nearer Earth stacks up against the outer boundary of the magnetosphere, throttling the interaction there and stopping solar material from entering.

Walsh and his colleagues compared observations from the ground and in space during a solar storm on Jan. 17, 2013.

This was a fairly moderate solar storm caused by a CME impacting Earth's magnetosphere for several hours. As the CME encountered the boundary of the magnetosphere, its magnetic fields and those around Earth realigned in a process called magnetic reconnection, which allowed energy and solar material to cross the boundary into the magnetosphere.

NASA's three THEMIS - for Time History of Events and Macroscale Interactions during Substorms - spacecraft were in the right place at the right time, flying through the magnetosphere's boundary approximately 45 minutes apart, and caught this interaction.

Closer to Earth, scientists could also study the sphere of cold dense gas at the very top of our atmosphere. This region is called the plasmasphere and it's made of what's known as plasma, a gas made of charged particles. GPS signals travel through the plasmasphere and they travel at different speeds depending on how thick or thin the plasmasphere is along the journey. Tracking the GPS radio signals, therefore, can help researchers map out the properties of the plasmasphere.

THEMIS showed that the tongue of this cold, dense plasmasphere material stretched all the way up to the magnetic reconnection point where the CME had made contact with the magnetopause. The three sets of THEMIS observations demonstrated that the plume had a dramatic impact on the characteristics of the magnetic reconnection region.

The study has been published in the journal Science Express.