Expert: Philip Stahl - 4/1/2007

Question
There are a few science-fiction stories which describe unusual massive solar flares which reach out from the Sun and wipe out all life on Earth in seconds. Is there any chance at all of such an event happening on either our Sun or that of any other, or are solar-flares 100% likely, due to astronomical theory,  to be only confined to within a star's immediate neighbourhood?

Answer
Hello,

The magnitude of solar flare described in the stories you reference is probably on a par with the massive flares observed on the star II Pegasi in Dec., 2005. These are about a hundred million times more powerful than the largest flares observed on the Sun.

They would, indeed, annhilate all life on Earth if they erupted from the Sun. You can read more about the II Pegasi flares at:

http://www.nasa.gov/mission_pages/swift/bursts/monster_flare.html

Fortunately for us, the Sun is an extremely stable star and the magnetic energy that can be primed for release is much, much less than on stars such as II Pegasi.

Since flare energy is directly related to the strength of the local magnetic field, and the tension-stress sustained by the field, then what we detect on the Sun are relative "small fry" flares compared to what was seen on II Pegasi.

About the worst that can happen for us, therefore, is akin to what occurred in 1973 when massive flares erupted and eroded about 20% of the Earth's ozone layer.

All flares, of course, hurl energetic particles far from their immediate vicinity and the Earth is no exception. We'd probably be in much worse shape when large flares occur were it not for our magnetosphere - which causes incoming particles (electrons, protons) to spiral in along magnetic field lines.

This sort of mechanism, also - interestingly - gives rise to the aurora.