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Planetary Defense: Protecting Earth from Asteroids
securitas writes "Space.com has published a feature about developing a planetary defense against catastrophic comet and asteroid impacts. The story arises from the aptly named 'Planetary Defense Conference: Protecting Earth from Asteroids' held in California February 23-26. The article discusses potential methods to prevent an impact, the need for study missions to comets and asteroids, the to-date haphazard approach to monitoring Near Earth Objects (NEOs), and the NASA/US Air Force Spaceguard Survey, which aims to discover and track 90% of 'Near Earth Asteroids (NEAs) with a diameter greater than 0.6 miles (1-kilometer) by 2008.' Some ideas for anti-impact technologies to develop include gas blasts, nuclear detonations, ramming microsatellites, lasers, mass drivers and gravitational tractor beams. The most disturbing message from the conference? 'It may take a celestial body hit to Earth' before governments take any meaningful steps to address this danger. Mirror at USA Today."
http://more.abcnews.go.com/sections/science/DailyN ews/asteroid0107.html
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http://home.att.net/~thehessians/asteroidstrike
http://www.sandia.gov/media/comethit.htm
http://www1.tpgi.com.au/users/tps-seti/crater.h
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For anyone who doesn't know, Lembit Opik[1] (Google will tell you all you want to know about him) was very largely responsible for getting this issue onto the political agenda.
Last time I was in the same room as him he was asked "OK, now you've got the politicians taking this seriously, when we spot one of these beggars coming towards us what do we do about it?"
His reply was that that wasn't his area of expertise; once politicians were taking the threat seriously they'd allocate money to the scientists and engineers, and a solution, if one were possible at all, was a done deal.
His lecture on how he got the politicians to take him seriously is well worth listening to; but actually I've found him rather good as a comic lecturer on several other subjects as well.
[1] Oh, and I'm sure slashdot geeks knew already that the "Oort cloud" is just shorthand for the "Oort-Opik cloud".
Everyday something hits earth, comets, mini asteroids, space dust. Most burns up in the atmosphere, but every so often something makes it through (meteorites) and hits the surface. True most of these meteorites are about the size of a golf ball or smaller.
I don't have time to comment my code, the program is late already.
RTFA. The so-called "tractor beams" discussed in the article are not sci-fi tractor beams at all. What they're proposing is flying by the asteroid with suitably heavy spacecraft that would attract the asteroid and nudge it off course.
You don't understand stats
The probability that an impact will occur within the decade is 50%. No more no less. It either happens or it doesn't happen.
Excuse me? Who doesn't understand stats? Just because an event can happen or not happen in a given time frame does not make the probability of that event 50%. By that reasoning I could say that either I'll win the lottery next week, or I won't therefore my odds are 50% (I wish).
An event with a 10% probability still happens or doesn't happen. Maybe I just don't understand what you're trying to say.... Like the rest of the post though.
It could be a bad virus that kills all mammals. Or the grey goo syndrome. Or global nuclear war. Or an ice age. Or an asteroid. Or if we're lucky and none of this happens, then in a few billion years, the Sun will expand, melt and disintegrate the Earth, and that'll be the end of it.
So, you see, we humans must (A) protect ourselves and (B) colonize other parts of the solar system or the galaxy.
Or we can just sit here and wait for doomsday and hope for a place in paradise.
To say that probability of something uncertain happening is "50% No more, no less" is a classic trap in misunderstanding the meaning of probability. Because an event has two possible states (does occur, does not occur) does NOT mean the probability of it occurring is 50%...This is degenerate and wrong thinking in probability. The best estimate of the probability of something happening is exactly equal to the rate at which that event occurred previously. This is called the base rate or prior probability and is integral to Bayes' theorem (please see this). Thus, if you flip a coin (of unknown fairness) 100 times and 41 of those flip come up heads, what's the best estimate of the probability that the next flip will be heads? 41%. [Side note: There are tests to determine if this rules out the coin being fair or not, but even these assume some a priori criterion for ruling out chance effects (i.e., "I'll call it unfair if the coin's pattern is likely to happen by chance less than 5% of the time"...this is called the "alpha level" of such tests).]
Anyway, there is a special distrubtion to describe the occurrence of random events in time (the Poisson distribution), but suffice it to say, the probability of an asteroid hitting the earth in the next decade is NOT 50%. This would only be true if, in the past, an asteroid has hit the earth (on average) once every other decade.
It's also interesting that movies pick the spectacular approach, even if it's wrong. Blowing up an asteroid with nuclear bombs does little to change the direction(lots of energy but not much momentum), and it multiplies the projectiles.
The current approach (and the above argument against nukes)was described by Freeman Dyson in 1995. Send out mass drivers to intercept the asteroids as early as possible. The earlier you start pushing, the less power you need(Quote: it's proportional to the inverse square of the warning time). Could well work- if you invest a lot in early warning systems, but for a movie, it's boring.
That reasoning will hold true for time-invariant random events, but the fact is that the asteroids up there move. Hence it can be more probable now than it was then (but I'd still like to see some evidence...maybe I'll RTFA...).
A good example would be if we observed an asteroid on course to hit earth. If the asteroid is a year away, it would be foolish to say that it is equally probable that earth would be hit by an asteroid this month as it would the month 12 months from now.
Even if we observed the asteroid on course to hit earth, it is still only a finite probability that it would hit earth because we cannot know the true course the asteroid would take exactly. So you would include a margin of error in your projections. We can use this margin of error to determine the probability. You find the range of the projection that would include earth getting hit and integrate the probabilities to find the current probability. That's at least the basics of it. In a real example you wouldn't have the probabilities of every possible deviation so you would have to assume a probability density for it (probably gaussian) and integrate that (or look it up in a table) to get the actual probability.
Of course if we don't know of any asteroids that are coming close to earth, the best we can probably do is the prior probability. But given the limited sampling time it's really a shot in the dark.
Note: by limited sampling time I was talking about how long we have been measuring meteor strikes...which hasn't been but infinitesimal part of the earth's lifetime. We may have evidence from rocks and remnants of craters, but there's no way we can know how many meteors fell without leaving evidence that we can examine today (meteors that land in the ocean leave smaller craters, and the earth is mostly ocean).
" The fact is, the Earth will be destroyed. All human life, no, all life, on Earth will be wiped out. It's just a matter of time."
Putting aside the sun expanding for a minute...
The earth has been hit with many asteroids. Never once has it destroyed all life. There is always something that survives and perpetuates. After the asteroid that destroyed the dinasaurs the dominant life on the planet was ferns for a very long time and eventually even human beings.
Humans will die (most of them anyway) but all life will not end.
The best way to support the US war effort is to continue buying American products.