Topeka, Kan. – A supernova could seriously harm life on Earth from much farther away than previously estimated, according to a new paper co-authored by Washburn University researcher and professor of astronomy and physics Brian Thomas.
“We now know that a supernova – the huge explosion of a massive star – occurred about 2.6 million years ago, about 150 light years from Earth,” Thomas said. “We examined the effects that it had on life here on Earth at the time.” Originally, researchers thought that a supernova might have to be as close as 25 light years away to cause mass extinctions. “Our work indicates that a supernova at 40 or 50 light years away would probably lead to widespread extinction on Earth.”
The new paper is based on evidence gathered over the last two years, including detailed studies of geological evidence from around the world. Thomas was part of a team of researchers, which included lead author Adrian Melott, professor of physics and astronomy at the University of Kansas, Michael Kacherlrieb of Institutt for fysikk in Norway, Dimitri Semikoz of the Ovservatoire de Paris, Sorbonne Paris Cite in France and the national Nuclear University in Moscow, and Andrew Overholt of MidAmerica Nazarene University.
Even at 150 light years away, very energetic “cosmic rays” from the supernova explosion would have gotten down into the lower atmosphere causing an increase in lightning storms. The lightning would have led to widespread wildfires.
“Atmospheric ionization can help lightning get started,” Thomas said. “When a cosmic ray comes down, it makes a path through the atmosphere knocking electrons out of atoms. The result would be a significant increase in cloud-to-ground lighting – the biggest cause of wildfires except for humans.”
The increase in wildfires could change the ecology of different regions such as the loss of tree cover in northeast Africa. And, in fact, the fossil record indicates that there was a loss of tree cover and an increase in grasslands approximately 2.6 million years ago right at the time of the supernova.
In addition to cosmic rays, the team found a supernova would have caused blue light to shine in the sky at night for about a month.
“While it doesn’t sound serious, that’s been shown to be a fairly bad thing for almost all living organisms,” Thomas said. “It throws off sleep and messes up your melatonin production.”
But, he noted, this effect would only last for a month or so and wouldn’t really show up in the fossil record.
“The most obvious consequences for Earth’s biology from a bathing in cosmic rays from a supernova would be an increase in cancer and the rate of mutations,” Thomas said.
The team looked at the fossil record in Africa for evidence to support their conclusion. They started there because Africa was the most stable continent during the Pleistocene epoch, when the supernova was likely to have occurred.
“We didn’t see a mass extinction, which might have happened if the supernova was closer to Earth, but we did see a lot of extinction going on at that time – a kind of turnover in species,” Thomas said. “We think this might have been the effect of the supernova either directly, or indirectly by causing climate change.”
The most significant changes in the climate, Thomas said, were likely to have come from the wildfires in the region – again, probably caused by the increase in lightning from the ionization. The Earth would have been protected somewhat by interstellar conditions.
“Cosmic rays don’t like to cross magnetic fields,” Thomas said, “but if they are oriented correctly, the cosmic rays would follow the field like a superhighway.”
Luckily for life on Earth, there was probably a weak, disorganized magnetic field, which helped to deflect at least some of the energy.
Fortunately for the current residents of the planet, supernovae shouldn’t top your list of worries. In fact, the nearest potential supernova is Betelgeuse which is about 600 light years away.
“That’s much further than the supernova 2.6 million years ago,” Thomas said. “If Betelgeuse went supernova, it would be spectacular in the sense that it would be bright and you’d see it in the daytime, but there wouldn’t be any harmful effects.”
“If you want to worry about something, pay attention to global warming and nuclear war,” he said. “There isn’t a potential supernova anywhere near us in the near future.”