A Supernova 50 Light-Years Away Could Start A Mass Extinction

Supernova Cassiopeia A is 10,000 light-years away. NASA/JPL-Caltech/STScI/CXC/SAO

The distance that a supernova would have a catastrophic impact on our planet's life-forms has been increased, as researchers have uncovered more clues on how these stellar explosions have influenced life on Earth.

Last year, researchers uncovered the global cooling effects that a nearby supernova brought to Earth. Now a different team has refined the measurement, cutting the distance of the explosion, which happened 2.6 million years ago, in half. Their work has been accepted for publication in the Astrophysical Journal.

"There's even more evidence of that supernova now," lead author Adrian Melott, from the Univerity of Kansas, said in a statement.

"The timing estimates are still not exact, but the thing that changed to cause us to write this paper is the distance. We did this computation because other people did work that made a revised distance estimate, which cut the distance in half. But now, our distance estimate is more like 150 light years."

Researchers think that this supernova was one in a series of such explosions and their cosmic rays might have contributed to changes in atmosphere and habitats in Africa between the Pliocene and the Pleistocene. Based on these effects, the new research suggests that a supernova might be deadly just 50 light-years away.

"People estimated the 'kill zone' for a supernova in a paper in 2003, and they came up with about 25 light years from Earth," Melott added.

"Now we think maybe it's a bit greater than that. They left some effects out or didn't have good numbers, so now we think it may be a bit larger distance. We don't know precisely, and of course, it wouldn't be a hard cutoff distance. It would be a gradual change. But we think something more like 40 or 50 light years. So, an event at 150 light years should have some effects here but not set off a mass extinction."

Exploding supernovae emit powerful light, neutrinos, and high-speed charged particles. The latter, which are commonly known as cosmic rays, could easily penetrate the Earth’s atmosphere if they originated nearby. At 150 light-years, they would be equivalent to a few CT scans per year. Not a lethal dose but enough to increase the incidence of cancer in animals.

Cosmic rays are also responsible for an increase in the ionization of the atmosphere leading to more lightning and wildfires, which could have been the cause for loss of forest in Africa a few million years ago. The vast effects of cosmic rays suggest that supernovae are terrifying even at what we believed to be a safe distant. But don’t worry, the closest star that might go off, Betelgeuse, is fortunately 600 light-years away.

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