Danger Zone

Earth protects us from many of the hazards of space. Its atmosphere and magnetic field block harmful radiation and particles, and destroy most incoming bits of space debris.

Yet the space environment remains dangerous. If a star exploded nearby, for example, it could wipe out the ozone layer, exposing life on Earth to deadly radiation. Fortunately, an exploding star would have to be even closer than astronomers had thought to pose a hazard. No stars within this range are of the exploding variety, so we should be safe for millions of years. That's the evaluation of astronomers from NASA and the University of Kansas.

They studied Earth's ozone layer, and the amount of harmful gamma rays and cosmic rays from supernovae -- stars that blast themselves to bits. If a supernova is close enough, its gamma rays and cosmic rays could damage Earth's ozone layer. That would allow ultraviolet energy from the Sun to stream through and damage or destroy much of the life on Earth.

But the astronomers found that a supernova would have to be within about 26 light-years to do any significant damage. Right now, the nearest stars that could someday explode as supernovae are hundreds of light-years away.

Our neighborhood changes over time, though, because stars all follow separate orbits around the galaxy. Even so, the astronomers calculated that, on average, one supernova should explode inside the danger zone every 670 million years.

(end)

Khorsheed.com – Oct 2003