- 3772 - SUPERNOVAE - close to us. A supernova is a star that has burned up all the hydrogen in its core and it explodes. How dangerous are nearby supernovae to life on Earth? A star more massive than our Sun runs out of hydrogen and becomes unstable. Eventually, it explodes and releases so much energy it can outshine its host galaxy for months. Our Sun would swallow the Earth
--------------------- 3772 - SUPERNOVAE - close to us.
- 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 living things.
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- Earth has experienced supernovae in its past. A supernova hasn’t been close enough to sterilize Earth, but there’s evidence showing supernovae have affected life on Earth.
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- Evidence exists of a supernova exploding near Earth about 2.6 million years ago. This supernova was about 160 light-years away. The supernova during 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 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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- A “type IIn 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.
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- After the x-rays arrive, the cosmic rays arrive. This is a double whammy for Earth’s ozone layer. Researchers aren’t sure about the lethal distances of supernovae. There are many variables, both in the progenitor star and its environment. The progenitor star’s mass loss is especially important.
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- By characterizing the lethal x-ray dose for Earth’s stratosphere and the energy output of some of the brightest supernova, scientists 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 the supernova’s 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. This upernova 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.
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. According to the researchers, SN2006jd was lethal to almost 100 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 the 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, the interacting X-ray phase of an sipernova’s evolution can entail significant consequences for terrestrial planets.
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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, yet researchers found undecayed 60Fe in ocean samples dating from 2 to 3 Myr ago. It should’ve decayed into nickel long ago. Supernovae can create 60Fe through nucleosynthesis when they explode.
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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.
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- It’s not the presence of these radioactive isotopes that poses a threat to life. It’s the radiation that must’ve struck Earth, and if the supernova that created the isotopes was close enough to spread them to Earth, then the radiation must’ve struck Earth, too.
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- Ionizing radiation from supernovae can alter Earth’s atmospheric chemistry from substantial distances. The initial burst of energy from an sunernova poses one threat, and so do the cosmic rays that arrive hundreds or thousands of years later and linger.
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- Another threat is x-rays that arrive months or years after the initial outburst. “Therefore, a corollary of the formidable threat found here is that this alters the timeline by which we know an supernova can influence a nearby planet. Thus it inflicted a high dosage of X-ray radiation on Earth’s atmosphere. The exact consequences are difficult for scientists to untangle. But 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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- This research has implications for habitability throughout the galaxy, too. The Galactic Habitable Zone 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.
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December 6, 2022 SUPERNOVAE - close to us. 3772
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