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Nearby Supernova Causes Mass Extinction?
hcg50a writes "AP has a
story on Yahoo about a theory that a blast of gamma rays from a distant supernova destroyed the earth's ozone layer, allowing normally shielded intense UV radiation from the sun to kill life on earth. The second-largest extinction in the Earth's history, the killing of two-thirds of all species, may have been caused by ultraviolet radiation from the sun after gamma rays destroyed the Earth's ozone layer. Astronomers are proposing that a supernova exploded within 10,000 light years of the Earth, destroying the chemistry of the atmosphere and allowing the sun's ultraviolet rays to cook fragile, unprotected life forms."
IANAP, but as I understand it, our own sun is too small to go supernova.
Just another wannabe fantasy novelist...
In 2003 this story was reported in nature.
And here the link to the pre print.
is in the article.
The galaxy has completed two rotations since the event, and given that the various components of the galaxy don't rotate perfectly synchronously, the remenant nebula is either not where you'd expect, or smeared out of all recognition.
Not necessarily. This happened 440 million years ago, it's quite conceivable that the system has moved massively in relation to us since then. (It was "only" 10,000 light years away as it was.)
You are not alone. This is not normal. None of this is normal.
You're right. Our sun is a dwarf star. It's death will be marked by expansion into a giant red star, then compression into a small core of oxygen and carbon, and finally lights out. Check out the BBC's page on the death of stars.
It has nothing to do with "approach vectors." Large objects don't usually fall in from outside the solar system.
The problem is leftover crumbs of planetary formation-- asteroids, planetesimals, the assorted random junk that has been circling the sun as long as the Earth has. In our system, Jupiter had the effect of removing that junk from our vicinity. It consumed a lot of rocks, and flung others out of the system by the slingshot effect. The remaining ones got shepherded into their own fairly circular orbits, in what we call the asteroid belt.
Without Jupiter (and the other giants), there would be lots more big rocks flying around the place. They also wouldn't be confined to the asteroid belt; they'd be zooming all over the place, and crossing over other planets' orbits. Those crossovers are what make a rock likely to hit a planet and cause extinctions.
Jupiter is not like a linebacker who jumps in front of asteroids for us. It's more like a maid, who swept the system clean a long time ago and made sure we wouldn't trip over anything.
The planet has reached a natural balance. The climate is stable. It's just very hot. The atmosphere is composed of heavier molecules than here on earth -- mostly CO2 -- so it can withstand much higher temperatures before being boiled off.
Why? Atmospheres "boil away" when the molecules in the atmosphere are moving faster than the escape velocity of the planet. But while particles in a hot gases move faster than those in cooler sample fo the same gas, gases made up of heavy and/or complex molecules will have lower particle speeds than gases made of light, simple molecules at the same temperature.
This is because temperature is related to energy: for two gases to have the same temperature means that the average energy of each particle is the same in the two gases. But heavy molecules reach the same kinetic energy at a lower speed (a molecule four times the weight reaches the same kinetic energy at only twice the speed). And just as importantly, complex molecules can store more energy in "internal modes" -- by spinning and vibrating. N2 and O2, the main constituents of earth's atmosphere, both have 1 vibrational and 2 rotational modes. CO2 is heavier, and has 3 vibrational and 3 rotational modes.
As a result, Venus's CO2-dominated atmosphere can be be much, much hotter before boiling off compared with earth's atmosphere. Probably the reason Venus's atmosphere is dominated by heavy elements and complex molecules is that the lighter stuff has already escaped.
The author of this post asserts his moral rights.