New Estimate Puts the Supernova Killzone Within 50 Light-Years of Earth

Composite Spitzer, Hubble, and Chandra image of supernova remnant Cassiopeia A. A new study shows that a supernova as far away as 50 light years could have devastating effects on life on Earth. (NASA/JPL-Caltech/STScI/CXC/SAO)

There are a lot of ways that life on Earth could come to an end: an asteroid strike, global climate catastrophe, or nuclear war are among them. But perhaps the most haunting would be death by supernova, because there’s absolutely nothing we could do about it. We’d be sitting ducks.

New research suggest that a supernova’s kill zone is bigger than we thought; about 25 light years bigger, to be exact.

Iron in the Ocean

In 2016, researchers confirmed that Earth has been hit with the effects from multiple supernovae. The presence of iron 60 in the seabed confirms it. Iron 60 is an isotope of iron produced in supernova explosions, and it was found in fossilized bacteria in sediments on the ocean floor. Those iron 60 remnants suggest that two supernovae exploded near our solar system, one between 6.5 to 8.7 million years ago, and another as recently as 2 million years ago.

Iron 60 is extremely rare here on Earth because it has a short half life of 2.6 million years. Any of the iron 60 created at the time of Earth’s formation would have decayed into something else by now. So when researchers found the iron 60 on the ocean floor, they reasoned that it must have another source, and that logical source is a supernova.

This evidence was the smoking gun for the idea that Earth has been struck by supernovae. But the questions it begs are, what effect did that supernova have on life on Earth? And how far away do we have to be from a supernova to be safe?

“…we can look for events in the history of the Earth that might be connected to them (supernova events).” – Dr. Adrian Melott, Astrophysicist, University of Kansas.

In a press release from the University of Kansas, astrophysicist Adrian Melott talked about recent research into supernovae and the effects they can have on Earth. “This research essentially proves that certain events happened in the not-too-distant past,” said Melott, a KU professor of physics and astronomy. “They make it clear approximately when they happened and how far away they were. Knowing that, we can consider what the effect may have been with definite numbers. Then we can look for events in the history of the Earth that might be connected to them.”

Earlier work suggested that a supernova kill zone is about 25-30 light years. If a supernova exploded that close to Earth, it would trigger a mass extinction. Bye-bye humanity. But new work suggests that 25 light years is an under-estimation, and that a supernova 50 light years away would be powerful enough to cause a mass extinction.

Supernovae: A Force Driving Evolution?

But extinction is just one effect a supernova could have on Earth. Supernovae can have other effects, and they might not all be negative. It’s possible that a supernovae about 2.6 million years ago even drove human evolution.

“Our local research group is working on figuring out what the effects were likely to have been,” Melott said. “We really don’t know. The events weren’t close enough to cause a big mass extinction or severe effects, but not so far away that we can ignore them either. We’re trying to decide if we should expect to have seen any effects on the ground on the Earth.”

Melott and his colleagues have written a new paper that focuses on the effects a supernova might have on Earth. In a new paper titled “A SUPERNOVA AT 50 PC: EFFECTS ON THE EARTH’S ATMOSPHERE AND BIOTA”, Melott and a team of researchers tried to shed light on Earth-supernova interactions.

The Local Bubble

There are a number of variables that come into play when trying to determine the effects of a supernova, and one of them is the idea of the Local Bubble. The Local Bubble itself is the result of one or more supernova explosion that occurred as long as 20 million years ago. The Local Bubble is a 300 light year diameter bubble of expanding gas in our arm of the Milky Way galaxy, where our Solar System currently resides. We’ve been travelling through it for the last five to ten million years. Inside this bubble, the magnetic field is weak and disordered.

Melott’s paper focused on the effects that a supernova about 2.6 million years ago would have on Earth in two instances: while both were within the Local Bubble, and while both were outside the Local Bubble.

The disrupted magnetic field inside the Local Bubble can in essence magnify the effects a supernova can have on Earth. It can increase the cosmic rays that reach Earth by a factor of a few hundred. This can increase the ionization in the Earth’s troposphere, which mean that life on Earth would be hit with more radiation.

Outside the Local Bubble, the magnetic field is more ordered, so the effect depends on the orientation of the magnetic field. The ordered magnetic field can either aim more radiation at Earth, or it could in a sense deflect it, much like our magnetosphere does now.

Focusing on the Pleistocene

Melott’s paper looks into the connection between the supernova and the global cooling that took place during the Pleistocene epoch about 2.6 million years ago. There was no mass extinction at that time, but there was an elevated extinction rate.

According to the paper, it’s possible that increased radiation from a supernova could have changed cloud formation, which would help explain a number of things that happened at the beginning of the Pleistocene. There was increased glaciation, increased species extinction, and Africa grew cooler and changed from predominantly forests to semi-arid grasslands.

Cancer and Mutation

As the paper concludes, it is difficult to know exactly what happened to Earth 2.6 million years ago when a supernova exploded in our vicinity. And it’s difficult to pinpoint an exact distance at which life on Earth would be in trouble.

But high levels of radiation from a supernova could increase the cancer rate, which could contribute to extinction. It could also increase the mutation rate, another contributor to extinction. At the highest levels modeled in this study, the radiation could even reach one kilometer deep into the ocean.

There is no real record of increased cancer in the fossil record, so this study is hampered in that sense. But overall, it’s a fascinating look at the possible interplay between cosmic events and how we and the rest of life on Earth evolved.

Sources:

What Was the Carrington Event?

What Was The Carrington Event?

Isn’t modern society great? With all this technology surrounding us in all directions. It’s like a cocoon of sweet, fluffy silicon. There are chips in my fitness tracker, my bluetooth headset, mobile phone, car keys and that’s just on my body.

At all times in the Cain household, there dozens of internet devices connected to my wifi router. I’m not sure how we got to the point, but there’s one thing I know for sure, more is better. If I could use two smartphones at the same time, I totally would.

And I’m sure you agree, that without all this technology, life would be a pale shadow of its current glory. Without these devices, we’d have to actually interact with each other. Maybe enjoy the beauty of nature, or something boring like that.

It turns out, that terrible burning orb in the sky, the Sun, is fully willing and capable of bricking our precious technology. It’s done so in the past, and it’s likely to take a swipe at us in the future.

I’m talking about solar storms, of course, tremendous blasts of particles and radiation from the Sun which can interact with the Earth’s magnetosphere and overwhelm anything with a wire.

Credit: NASA

In fact, we got a sneak preview of this back in 1859, when a massive solar storm engulfed the Earth and ruined our old timey technology. It was known as the Carrington Event.

Follow your imagination back to Thursday, September 1st, 1859. This was squarely in the middle of the Victorian age.

And not the awesome, fictional Steampunk Victorian age where spectacled gentleman and ladies of adventure plied the skies in their steam-powered brass dirigibles.

No, it was the regular crappy Victorian age of cholera and child labor. Technology was making huge leaps and bounds, however, and the first telegraph lines and electrical grids were getting laid down.

Imagine a really primitive version of today’s electrical grid and internet.

On that fateful morning, the British astronomer Richard Carrington turned his solar telescope to the Sun, and was amazed at the huge sunspot complex staring back at him. So impressed that he drew this picture of it.

Richard Carrington’s sketch of the sunspots seen just before the 1859 Carrington event.

While he was observing the sunspot, Carrington noticed it flash brightly, right in his telescope, becoming a large kidney-shaped bright white flare.

Carrington realized he was seeing unprecedented activity on the surface of the Sun. Within a minute, the activity died down and faded away.

And then about 5 minutes later. Aurora activity erupted across the entire planet. We’re not talking about those rare Northern Lights enjoyed by the Alaskans, Canadians and Northern Europeans in the audience. We’re talking about everyone, everywhere on Earth. Even in the tropics.

In fact, the brilliant auroras were so bright you could read a book to them.

The beautiful night time auroras was just one effect from the monster solar flare. The other impact was that telegraph lines and electrical grids were overwhelmed by the electricity pushed through their wires. Operators got electrical shocks from their telegraph machines, and the telegraph paper lit on fire.

What happened? The most powerful solar flare ever observed is what happened.

In this image, the Solar Dynamics Observatory (SDO) captured an X1.2 class solar flare, peaking on May 15, 2013. Credit: NASA/SDO

A solar flare occurs because the Sun’s magnetic field lines can get tangled up in the solar atmosphere. In a moment, the magnetic fields reorganize themselves, and a huge wave of particles and radiation is released.

Flares happen in three stages. First, you get the precursor stage, with a blast of soft X-ray radiation. This is followed by the impulsive stage, where protons and electrons are accelerated off the surface of the Sun. And finally, the decay stage, with another burp of X-rays as the flare dies down.

These stages can happen in just a few seconds or drag out over an hour.

Remember those particles hurled off into space? They take several hours or a few days to reach Earth and interact with our planet’s protective magnetosphere, and then we get to see beautiful auroras in the sky.

This geomagnetic storm causes the Earth’s magnetosphere to jiggle around, which drives charges through wires back and forth, burning out circuits, killing satellites, overloading electrical grids.

Back in 1859, this wasn’t a huge deal, when our quaint technology hadn’t progressed beyond the occasional telegraph tower.

Today, our entire civilization depends on wires. There are wires in the hundreds of satellites flying overhead that we depend on for communications and navigation. Our homes and businesses are connected by an enormous electrical grid. Airplanes, cars, smartphones, this camera I’m using.

Credit: Wikimedia Commons.

Everything is electronic, or controlled by electronics.

Think it can’t happen? We got a sneak preview back in March, 1989 when a much smaller geomagnetic storm crashed into the Earth. People as far south as Florida and Cuba could see auroras in the sky, while North America’s entire interconnected electrical grid groaned under the strain.

The Canadian province of Quebec’s electrical grid wasn’t able to handle the load and went entirely offline. For 12 hours, in the freezing Quebec winter, almost the entire province was without power. I’m telling you, that place gets cold, so this was really bad timing.

Satellites went offline, including NASA’s TDRS-1 communication satellite, which suffered 250 separate glitches during the storm.

And on July 23, 2012, a Carrington-class solar superstorm blasted off the Sun, and off into space. Fortunately, it missed the Earth, and we were spared the mayhem.

If a solar storm of that magnitude did strike the Earth, the cleanup might cost $2 trillion, according to a study by the National Academy of Sciences.

The July 23, 2012 CME would have caused a Carrington-like event had it hit Earth. Thankfully for us and our technology, it missed. Credit: NASA’s Goddard Space Flight Center

It’s been 160 years since the Carrington Event, and according to ice core samples, this was the most powerful solar flare over the last 500 years or so. Solar astronomers estimate solar storms like this happen twice a millennium, which means we’re not likely to experience another one in our lifetimes.

But if we do, it’ll cause worldwide destruction of technology and anyone reliant on it. You might want to have a contingency plan with some topic starters when you can’t access the internet for a few days. Locate nearby interesting nature spots to explore and enjoy while you wait for our technological civilization to be rebuilt.

Have you ever seen an aurora in your lifetime? Give me the details of your experience in the comments.