- 3726 - SUPERNOVAE - how close can it get? Ionizing radiation from supernovae can alter Earth’s atmospheric chemistry. The initial burst of energy from a supernova poses one threat, and so do the cosmic rays that arrive hundreds or thousands of years later. X-rays can arrive months or years later.
--------------------- 3726 - SUPERNOVAE - how close can it get?
- How dangerous are nearby supernovae to life on Earth? From a distance, supernovae explosions are fascinating. A star more massive than our Sun runs out of hydrogen and becomes unstable. It explodes and releases so much energy it can outshine its host galaxy for months.
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- But space is vast and largely empty, and supernovae are relatively rare. And most planets don’t support life, so most supernovae probably explode without affecting any living things.
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- One type of supernova has a more extended reach than thought. It could have consequences for planets like ours. Earth is no stranger to supernovae. One hasn’t been close enough to sterilize Earth, but there’s evidence showing supernovae have affected life on Earth.
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- A 2018 paper presented evidence of a supernova exploding near Earth about 2.6 million years ago. It was about 160 light-years away. The supernova was tied to the “Pliocene marine megafauna extinction“. In that event, up to a third of Earth’s large marine species were wiped out, but only in shallow coastal waters.
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- Up to 20 supernovae have showed up in the last 11 million years. Some of these were as close as 130 light-years to Earth. About 2 million years ago, one of the supernovae exploded close enough to our planet to damage the ozone layer.
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- There are different types of supernovae. Some of them have a much longer reach and much greater duration. Scientists have long known about the powerful gamma rays that supernova release during the explosion. They also know about the cosmic rays that can arrive hundreds or thousands of years later. If this happens close enough to a planet like Earth, the cosmic rays can deplete the ozone layer and increase muon radiation at the surface.
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- An X-ray luminous supernova is different from other supernovae. When a supernova explodes, it emits gamma rays and other photons immediately. In an x-ray luminous supernova, gamma rays and photons are emitted, but some of the radiation from the explosion interacts with a dense circumstellar medium surrounding the progenitor star. This creates X-rays that can be lethal up to 160 light-years away.
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- In a scenario where an supernova exploded close to Earth, it can take months or years following the initial explosion for the X-rays to arrive. Interactions with the circumstellar debris cause a delay. The X-rays can deplete Earth’s ozone layer, allowing harmful ultraviolet radiation from the Sun to reach the planet’s surface. After the X-rays arrive, the cosmic rays arrive. Cosmic rays are not really rays they are atomic nuclei, protons and electrons.
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- What are the lethal distances for supernovae? There are many variables, both in the progenitor star and its environment. The progenitor star’s mass loss is especially important. But by characterizing the lethal X-ray dose for Earth’s stratosphere and the energy output of some of the brightest supernova. The astronomers calculated the lethal distance for some well-known supernovae:
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- SN 1987A exploded in the Large Magellanic Cloud, and the light reached Earth in 1987. Scientists observed the explosion and confirmed the source of energy for visible light for the first time. It proved that the long-duration glow after an explosion is radioactive.
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- SN1987A wasn’t very lethal. They say the supernova was only deadly to a distance of less than one light-year. It was the least dangerous supernova out of the 31 the team characterized.
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- The most lethal of the 31 was “SN2006jd“ . It exploded in the galaxy NGC 4179, about 57 million light-years away, and the light reached Earth in 2006. SN2006jd was lethal out to almost 100 light-years.
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- The five most lethal supernova in this study are all “Type Iin” supernovae, as are seven of the top ten. The top five are all “Type Iin” x-ray luminous supernovae, and so are seven of the top ten. Type IIn supernovae also have the greatest range of influence.
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- SN 2006jd has a range of influence that spans from 30 parsecs to 60 parsecs (100 light-years to 200 light-years.).
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- Our Solar System is inside what’s known as the “Local Bubble“. It’s a cavity carved out of space in the Milky Way’s Orion Arm. Multiple supernovae explosions created the bubble in the last 10 to 20 million years.
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- Advances in X-ray astronomy will shed more light on the consequences for terrestrial planets, there’s lots more to uncover. The interacting X-ray phase of an supernova’s evolution can entail significant consequences for terrestrial planets. The evidence certainly points to this process as capable of imposing lethal consequences for life at formidable distances.
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- Scientists know that supernovae have had some effect on Earth. The presence of the radioactive isotope 60Fe has a half-life of 2.6 million years. Researchers have found undecayed 60Fe in ocean samples dating from 2 to 3 Million years ago. It should have decayed into nickel long ago. Supernovae can create 60Fe through nucleosynthesis when they explode.
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- But other things can create 60Fe. Asymptomatic giant branch stars can make it, too.
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- Researchers also found 53Mn in the same samples of ferromanganese crust that hold the 60Fe. It’s also a radioactive isotope that should’ve decayed by now. Unlike 60Fe, only supernovae can create 53Mn. Its presence is definite proof of nearby supernovae in the recent geological past. “Fe” is iron amd “Mn” is magnesium.
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- Ionizing radiation from supernovae can alter Earth’s atmospheric chemistry from substantial distances. The initial burst of energy from a supernova poses one threat, and so do the cosmic rays that arrive hundreds or thousands of years later and linger. X-rays can arrive months or years after the initial outburst.
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- Supernova outbursts have almost certainly struck our planet. If the radiation weakened the ozone layer, allowing more UV radiation to reach the Earth’s surface, it would’ve caused mutations. It’s called UV mutagenesis, which may have driven molecular evolution and been critical in the origin of sex. In fact, mutation is evolution’s primary driver.
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- The Galactic Habitable Zone (GHZ) is a region in a galaxy where habitability is most likely. Since supernovae can be fatal for life if close enough, regions with many stars that can potentially explode as supernovae are less habitable. Supernovae can be lethal at greater distances than thought and can be fatal in the period of a few months or years after the initial outburst due to the X-rays.
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- October 31, 2022 SUPERNOVAE - how close can it get? 3726
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