What is Geomagnetic storm, which destroyed 40 SpaceX satellites?

Up to 40 SpaceX high-speed internet satellites have been knocked out of orbit by a geomagnetic storm shortly after launch. 

But the company said they pose little threat to Earth as they burn up in the atmosphere. 

Geomagnetic storms are caused by ejections of the solar corona into space, resulting in disturbances to the Earth's upper atmosphere and increased drag on objects in low orbits. 

The latest 49 satellites from the Starlink network launched from the Kennedy Space Center in Florida on February 3 and successfully assumed their initial orbit, with their nearest approach to the surface 210 kilometres high.

On February 4, however, they were struck by the space weather event, Elon Musk's company said in a statement late Tuesday.