How Will Humans Meet Their End? 5 Cosmic Risks

On Sunday, an asteroid passes close to Earth, reminding us once again that our existence on this planet is fragile. Humanity will, in fact, meet its end someday, but whether it's tomorrow or millennia from now is all just speculation, even if the threats to the planet are very real.
We have a morbid fascination with our own demise: Doomsday cults gather on mountaintops waiting for the Rapture or commit mass suicide, while other people fret over the prophecies of the Mayans or Nostradamus. And while judgment days come and go, these prophecies prey on our worries that humankind is ephemeral: We know it is just a matter of time until we stop inhabiting the Earth.
But even as zealots and psychics like to guess the date of our demise, there are real risks to our existence, and many doomsday scenarios are actually discussed among scientists and rational people. They run the gamut from natural disasters to plagues; and of course, the biggest and most imminent threat to our survival: global warming.
Can people be destroyed by heavens above us? Here are five frequently deliberated scenarios and the reality behind them.
[[{"type":"media","view_mode":"media_original","fid":"586528","attributes":{"alt":"","class":"media-image media-image-right","height":"750","style":"width: 350px; height: 263px; margin-left: 4px; margin-right: 4px; float: right;","typeof":"foaf:Image","width":"1000"}}]]1. Asteroid Impact. The Earth is pummeled by hundreds of tons of space rocks a year, but most of them burn up high in our atmosphere, producing shooting stars or spectacular meteor showers. Larger impacts, like the Chelyabinsk meteor that exploded over Russia last year, are much more rare, occurring every few decades or so. That space rock, which was about 20 meters in diameter, injured about 1,000 people, mostly from shattering glass from the shock of its impact. But as the Earth is more than 70 percent water, many meteors of this size strike the planet, but go unnoticed by us.
However, many asteroids have collided with Earth and have caused great damage in our recent geological history. The Chicxulub asteroid, which was about 10-15 kilometers wide, is believed to have caused the mass extinction of dinosaurs 66 million years ago when it landed in the northern Yucatán Peninsula. But what effect would a large asteroid of this size have on civilization today?
Astronomers scour our skies, keeping a vigil at night so we don’t have to. NASA has two programs actively searching for large asteroids, one called the Asteroid Initiative and the other the Near Earth Observation Program, also known as “Spaceguard.” The scientists who work for these programs say it would take an asteroid about a 10th the size of Chicxulub to wipe out humankind. Asteroids of this size strike the Earth on average once every half million years at best.
Recently, there have been many media reports of an asteroid, discovered by Ukrainian scientists, which has the potential to wipe out the planet in 2036. But while the asteroid, called 2013 TV135, will likely make a close pass, NASA researchers says their calculations show its chances of striking the Earth are under .0021%. So despite the dire warnings from the media, there is very little to worry about.
Still, NASA scientists are looking at technologies to divert such asteroids if they ever do pose a risk. The current ideas for shielding us from asteroids vary greatly. Two still being considered are blowing it to smithereens with a nuclear bomb, and gently pushing it off course with kinetic interceptors (possibly using nuclear bombs as well). While the first solution makes for better Hollywood, the consensus from scientists is that nudging a killer asteroid off course is the smarter alternative.
[[{"type":"media","view_mode":"media_original","fid":"586526","attributes":{"alt":"","class":"media-image media-image-right","height":"812","style":"width: 350px; height: 244px; margin-left: 4px; margin-right: 4px; float: right;","typeof":"foaf:Image","width":"1000"}}]] 2. Solar Superstorm. Astronomers agree that a giant storm on the surface of the sun will eventually cause a great calamity on Earth, but there’s doubt whether it will be enough to end humankind.
The probability of a solar superstorm big enough to wreak havoc on the planet is real. The chances of one having an impact on the Earth in the next decade is about 12% according to NASA scientists. And only two years ago, such a storm erupted from the sun's surface, but luckily the blast was not directed at us. Had it occurred a week earlier, it could have been one of the worst geomagnetic storms in more than 400 years, sending billions of tons of highly charged particles into the planet’s magnetic field and destroying electrical grids worldwide, for months or even years.
Some scientists speculate that near the end of the last Ice Age, there was a large solar superstorm that led to the sudden disappearance of many mammalian species. In a paper published in the journal Radiocarbon, Paul LaViolette, the controversial astrophysicist and founder of the Starburst Foundation, claims that a large solar flare, which occurred some 12,900 years ago, primarily led to the demise of mammals weighing between 55 and 110 pounds.
NASA says the intense bursts of electromagnetic energy and particles showering the Earth from a solar storm caused by a coronal mass ejection are not physically capable of destroying Earth or its inhabitants, but they could shut down everything from cellphones to air travel. NASA and the National Oceanic and Atmospheric Administration Space Weather Prediction Center, which monitors “solar weather,” say that the sun’s superstorms can be predicted and they can issue warnings to electric utilities, spacecraft operators and airline pilots before a coronal mass ejection makes its way to Earth. Electrical and electronic systems can be shut down during the storm and turned back on when the storm subsides. We could actually wait out a solar superstorm the same way coastal communities wait out hurricanes. When it’s over we’ll be able to resume our lives — even if they are greatly altered — conclude many scientists.
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3. Supernova. If a star were to die in a nearby solar system, the resulting supernova explosion could come close enough to the Earth to have devastating effects on the biosphere. The gamma-ray radiation would have the most deadly impact by depleting the Earth’s ozone layer enough to expose us to harmful solar and cosmic radiation. The first lifeforms that would die off would be the ocean’s phytoplankton and then famine and pestilence would move up the food chain. Eventually, we would meet our demise through starvation, if the radiation doesn’t kill us first.
On average, a supernova explosion occurs within 33 light years of the Earth every 240 million years and scientists say it would take an event some 25 light years away to significantly deplete the Earth’s ozone layer. Astronomers, however, have a good idea which stars are on their way to becoming supernovas. One prominent candidate nearby is the red giant Betelgeuse. But at 643 light years, a supernova event on that star wouldn’t have deadly impact here. However, it might make for a beautiful evening sky spectacle.
More worrisome are white dwarf stars, which are much more unpredictable. It would take a supernova from a white dwarf no more than 25-35 light years away to have a devastating impact here. The closest known white dwarf which is a candidate is IK Pegasi, but astronomers say its velocity relative to our solar system make it less of a threat every day as it moves a safe distance away.
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The studies, one at the Paris Observatory and the other at UC Santa Cruz concurred that there is about a 1% chance Mercury's orbit, which is already notably odd, could become unstable sometime during the lifespan of our sun. Numerous simulations based on this theory produced four major outcomes, with Mercury either colliding into the Sun, Venus, or Earth, or being flung from the solar system altogether without inflicting any damage.
No doubt, if a planet the size of Mercury crashed into the Earth, all life here would be annihilated. However the chances of this scenario playing out are exceedingly slim, say scientists. In fact, their simulations indicate a 99% chance that the planets will stay in their current orbits for the next 5 billion years, and by that time the sun will have expanded into a red giant star, swallowing up the innermost four planets.  
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The European Space Agency’s Ulysses spacecraft has shown that the kind of galactic dust that’s found in dark nebulae is passing through our solar system more than normal, but that doesn't necessarily mean we're passing through a dark nebula. So far, the sun’s magnetic field has been able to shield the planet from most of this stardust, but recent studies have shown that it's losing its protective power, so about three times more dust than usual is now passing through the solar system at a very high rate.
It’s conceivable that an increase in the amount of dust in the solar system will create more cosmic dust as it impacts asteroids and comets, say researchers, which adds to the extraterrestrial material that rains down on Earth. Some scientists speculate that a great amount dust entering in the solar system and Earth’s atmosphere could conceivably create a “nebula winter” or a great environmental catastrophe with various forces acting to cool the planet, destroy the ozone layer and deplete it of oxygen.
These researchers theorize that nebula winters are behind Earth’s repeated Ice Ages and mass extinctions. The phenomenon is sometimes called “snowball Earth” and eons-old supernovae and star bursts are claimed to be the culprits behind the nebulae that move throughout the galaxy. Increased cosmic dust from these galactic events many light years away is theorized to have reached our atmosphere and decreased solar radiation on the surface, resulting in global cooling.
In the coming weeks, we will look at the theories of human extinction through warfare, pandemics, ecological disasters, geophysical catastrophic events, manmade global warming, overpopulation, and technological accidents.

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