A sunspot five times the size of Earth could wreak havoc with satellites and radio communication systems, scientists warn, as it moves across the face of the sun and Earth moves directly into its firing line.

Seven huge X-class flares have already erupted from the spot, including one of magnitude X17 last Wednesday that made it into the record books as the fourth largest ever seen.

The US National Oceanic and Atmospheric Administration (NOAA) said that the flares have already caused problems with some electric power systems, radio communications and global positioning equipment.

It went on to warn that further flares are likely in the next week, and because the sunspot is moving into line with Earth, the risk of disruptions is even greater as the solar activity will strike the planet head-on.

The daddy of all solar flares was spotted in November 2003, and ranked X28 on the magnitude scale. Fortunately, the flare did not directly strike Earth. Even so, it did disrupt satellites, and caused some problems for the Mars Express spacecraft, which at that time was still en route to Mars.

The radiation from a flare will reach the Earth within minutes, but the charged particles associated with the event take longer to arrive, typically two days. These particles are responsible for the Auroras Borealis and Australis; the Northern and Southern lights.

These plasma storms are also responsible for interfering with power grids, TV reception, satellites and so on. In 1989 a solar flare that hit the Earth directly actually knocked out a whole power grid in Quebec. ®