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Posted on 09/26/2009 9:43:01 PM PDT by LibWhacker
Stephen Hawking believes that one of the major factors in the possible scarcity of intelligent life in our galaxy is the high probability of an asteroid or comet colliding with inhabited planets. We have observed, Hawking points out in Life in the Universe, the collision of a comet, Schumacher-Levi, with Jupiter (below), which produced a series of enormous fireballs, plumes many thousands of kilometers high, hot "bubbles" of gas in the atmosphere, and large dark "scars" on the atmosphere which had lifetimes on the order of weeks.
It is thought the collision of a rather smaller body with the Earth, about 70 million years ago, was responsible for the extinction of the dinosaurs. A few small early mammals survived, but anything as large as a human, would have almost certainly been wiped out.
Through Earth's history such collisions occur, on the average every one million year. If this figure is correct, it would mean that intelligent life on Earth has developed only because of the lucky chance that there have been no major collisions in the last 70 million years. Other planets in the galaxy, Hawking believes, on which life has developed, may not have had a long enough collision free period to evolve intelligent beings.
Sl9calar“The threat of the Earth being hit by an asteroid is increasingly being accepted as the single greatest natural disaster hazard faced by humanity,” according to Nick Bailey of the University of Southampton's School of Engineering Sciences team, who has developed a threat identifying program.[ Image: Comet Shoemaker-Levy 9 collision with Jupiter]
The team used raw data from multiple impact simulations to rank each country based on the number of times and how severely they would be affected by each impact. The software, called NEOimpactor (from NASA's "NEO" or Near Earth Object program), has been specifically developed for measuring the impact of 'small' asteroids under one kilometer in diameter.
Early results indicate that in terms of population lost, China, Indonesia, India, Japan and the United States face the greatest overall threat; while the United States, China, Sweden, Canada and Japan face the most severe economic effects due to the infrastructure destroyed.
The top ten countries most at risk are China, Indonesia, India, Japan, the United States, the Philippines, Italy, the United Kingdom, Brazil and Nigeria.
Astrofisico_Stephen_Hawking“The consequences for human populations and infrastructure as a result of an impact are enormous,” says Bailey. “Nearly one hundred years ago a remote region near the Tunguska River witnessed the largest asteroid impact event in living memory when a relatively small object (approximately 50 meters in diameter) exploded in mid-air. While it only flattened unpopulated forest, had it exploded over London it could have devastated everything within the M25. Our results highlight those countries that face the greatest risk from this most global of natural hazards and thus indicate which nations need to be involved in mitigating the threat.”
What would happen to the human species and life on Earth in general if an asteroid the size of the one that created the famous K/T Event of 65 million years ago at the end of the Mesozoic Era that resulted in the extinction of the dinosaurs impacted our planet.
As Stephen Hawking says, the general consensus is that any comet or asteroid greater than 20 kilometers in diameter that strikes the Earth will result in the complete annihilation of complex life - animals and higher plants. (The asteroid Vesta, for example, one of the destinations of the Dawn Mission, is the size of Arizona).
How many times in our galaxy alone has life finally evolved to the equivalent of our planets and animals on some far distant planet, only to be utterly destroyed by an impact? Galactic history suggests it might be a common occurrence.
The first this to understand about the KT event is that is was absolutely enormous: an asteroid (or comet) six to 10 miles in diameter streaked through the Earth's atmosphere at 25,000 miles an hour and struck the Yucatan region of Mexico with the force of 100 megatons -the equivalent of one Hiroshima bomb for every person alive on Earth today. Not a pretty scenario!
Recent calculations show that our planet would go into another "Snowball Earth" event like the one that occurred 600 million years ago, when it is believed the oceans froze over (although some scientists dispute this hypothesis -see link below).
While microbial bacteria might readily survive such calamitous impacts, our new understanding from the record of the Earth's mass extinctions clearly shows that plants and animals are very susceptible to extinction in the wake of an impact.
Impact rates depend on how many comets and asteroids exist in a particular planetary system. In general there is one major impact every million years -a mere blink of the eye in geological time. It also depends on how often those objects are perturbed from safe orbits that parallel the Earth's orbit to new, Earth-crossing orbits that might, sooner or later, result in a catastrophic K/T or Permian-type mass extinction.
VredefortThe asteroid that hit Vredefort located in the Free State Province of South Africa is one of the largest to ever impact Earth, estimated at over 10 km (6 miles) wide, although it is believed by many that the original size of the impact structure could have been 250 km in diameter, or possibly larger(though the Wilkes Land crater in Antarctica, if confirmed to have been the result of an impact event, is even larger at 500 kilometers across). The town of Vredefort is situated in the crater (image).
Dating back 2,023 million years, it is the oldest astrobleme found on earth so far, with a radius of 190km, it is also the most deeply eroded. Vredefort Dome Vredefort bears witness to the world’s greatest known single energy release event, which caused devastating global change, including, according to many scientists, major evolutionary changes.
What has kept the Earth "safe" at least the past 65 million years, other than blind luck is the massive gravitational field of Jupiter, our cosmic guardian, with its stable circular orbit far from the sun, which assures a low number of impacts resulting in mass extinctions by sweeping up and scatters away most of the dangerous Earth-orbit-crossing comets and asteroids
If a “KT event” were to happen again...it would be a very large pile of not good.
Think how lucky the dinos were, they had no knowledge of asteroids or collisions, just lived along until Whammo, death from the sky. BTW, if we are hit every million years then it has skipped many, many millions of years. The dinos lived for far more than a million(about 185 million)before being smacked(if that is what actually happened) and reptiles were around for serveral hundred million before the Dinos came along. As the article points out it has been 70 million years since the Dinos went under.
So that begs the question: If only one major Asteroid has hit earth over the last 500 million years or so, how do they come up with the "once every million years" figure? BTW, I believe there was one other major extinction of life they didn't mention here, after the Dinos.
It’s a game of pinball, bowling, or marbles on a cosmic scale...
http://www.youtube.com/watch?v=LyzIau5dBao&feature=related
“advanced life”... sounds like the DU’rs will get by unscathed. (and, sadly, a few freepers...)
Right, this article is a badly edited version of a longer talk Hawking gave. A link to that talk is on the Daily Galaxy website. Haven’t read it yet, myself, so I don’t know if he was more careful than the editor, BUT I’m pretty sure he’s talking about asteroids measuring one kilometer or more in diameter. Those do hit us about once every million years. The 10 kilometer monsters, like the one that got the dinosaurs, hit about every 100 million years.
Obvious Hand of God ping!
“The first this to understand about the KT event is that is was absolutely enormous: an asteroid (or comet) six to 10 miles in diameter streaked through the Earth’s atmosphere at 25,000 miles an hour and struck the Yucatan region of Mexico with the force of 100 megatons -the equivalent of one Hiroshima bomb for every person alive on Earth today. Not a pretty scenario! “
Let’s see ... 100 megatons = 100 x 10^6 / 12.5 x 10^3 (Hiroshima bomb yield) = 10,000.
Correct me if I’m wrong here, but 10,000 does not quite equal 6,000,000,000.
Maybe they meant gazilliatons?
Today, a land impact of a 100-meter diameter meteor or comet will cause ENORMOUS long-term damage, not only will we have the shockwave from the impact (both through severe ground shaking and the gigantic air blast effect), but the impact will kick up a huge amount of dirt and rocks that will rain down potentially a couple of thousand miles away--and the debris will be a hotter than the melting point of lead. Such an impact will cause essentially a nuclear winter as all the impact debris thrown up in the air severely cuts the amount of light from the Sun possibly for a couple of years.
20 kilotons = 2 x 104 tons
Go!
Ah ... now that makes sense. But it’s not how the article was writen. Went to wiki. They say 100 million megatons, too.
written ... whatever.
1014/(2x104) = 5 x 109.
More if you use 12.5 kilotons for Hiroshima. Or perhaps this talk was 10 years ago and Hawking was using 20 kilotons for Hiroshima. I've always heard 20 kilotons. In any event, way more than 10,000.
Agreed. But the articles says “100 megatons,” hence my comment.
Did I read that wrong? Going back to check ...
Nope, I read it correctly. :)
Lol, okay as long as we agree that the impact released as much energy as 5 or 6 billion Hiroshima bombs, roughly one Hiroshima-sized bomb for every person on Earth (and not enough for only 10,000 people). Ten thousand Hiroshimas is nothing in comparison. Cheers! :-)
The probability of asteroid impacts is one of the factors I have argued is omitted from the Drake Equation for calculating the likelihood of intelligent alien life, and significantly reduces the probabilities of other such life.
Most stars in the Milky Way are clustered in the Galaxy Center, unlike Sol out in the relatively spacious spiral arms. Stars being more densely packed would increase the gravitational influence on nearby stars, unsettling their own Oort Clouds and driving in killer comets and asteroids towards the inner rocky worlds.
>>>How many times in our galaxy alone has life finally evolved to the equivalent of our planets and animals on some far distant planet, only to be utterly destroyed by an impact? Galactic history suggests it might be a common occurrence.
As far as I know, there is no such evidence of external life whatsoever. Comets and asteroids we have confirmed and studied. Alien life is just a hope, not something so casually to assume.
It should say, "100 million megatons."
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