h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

well ok.

I wasn't really besing what i said on any known fact. That's why I put in the bit about correcting me. The movies haven't really affected what I think about this particular subject. I hate disaster movies. But thanks for clearing up the misconceptions I DID have.

That's what discussion is about after all. But then, it seems the only possible solution is to get everybody off the Earth as soon as possible without being sure of a threat. If an asteroid was found hurtling towards Earth (let's be generous and give it ten hours) then you couldn't possibly make arrangement for anybody to get away safely in any way whatsoever. The rockets would have to be fueled and on stand-by 24-7. And there would have to be hundreds of them!

Would a rock large enough to completely wipe out life on Earth create a shock of any sort outwith the atmosphere? Could this shock be powerful enough to hit something close to the Earth like the moon or a hundred rockets on their way to it? I'm just asking.

two points of correction.

first, we know how often (on average) rocks of different sizes hit from the historical record. based on those statistics we know that a tunguska sized object is overdue, and a continent devestator is very likely in the next 35 thousand years (+/- 50 thousand).

secondly, orbital prediction is not as hard as you make out. the problem is you need weeks of data to make an acurate preduction, and if you don't spot it until late, there is no time to do anything.#

also, if you were to send up bruce willis in a shuttle, with only 6 hours to go he would just become a smear a bit earlier. to roundevous with an asteroid you need to sneak up behind it. then you need time to have your course correction make a difference. If we have 10 years warning, we can probably do something. if we have a couple of months, it is time to have a good holiday, because there is no time to do anything else.

How does "overdue" mean anything? Surely there not having been an asteroid in the recent past doesn't make it any more likely that there will be one in the near future?

Bouncy's right.

How could you possibly predict a random event? Space IS big.

Which brings up annother point. If, in the future, we manage to build colonies on the moon or even Mars we will soon be able to expand to other planets.

From further into space we can make new discoveries and even perhaps give ample warning to Earth if an asteroid is spotted. Then it's just a matter of getting as many people as possible to a colony on a different planet. It'll be a long long time before we can make those advances, but it may also be a long time before a rock of that size decides to crop up. We don't know. But we do know that we're on our way, at least.

A few observations:

First of all, I'm not suggesting that we get EVERYONE off the earth. For a start, not everyone would survive a launch using rocket technology, and until there's a space elevator, that's all we've got. The accelerations would kill or injure a significant proportion of the population. And that's saying nothing about people who wouldn't WANT to go. Besides, take everyone off earth and put them all on Mars, and you just have the same problem, only worse. Our best strategy is to spread ourselves as widely as possible so that no single planetary-scale event can wipe us out. For that we need sustainable, self-sufficient colonies, on at least two different bodies (e.g. earth and moon, earth and mars), neither dependent on the other.

Second, the idea of a medium sized impact being "due" is a reasonable simplification. If I tossed a coin ten times, and it came up heads ten times, then most people would say that a tail was "due". It isn't, of course, the odds are still fifty-fifty. But you expect, over the long run, fifty-fifty, so the longer the run of heads continues, the greater the tension waiting for the tail to turn up, as it inevitably will.

In reality, impacts are random events. We get them about every x million years - but by the nature of a random event, it's possible we could go a very, very long time between them, or it's possible we could get two in the same week. Both of these scenarios are unlikely.

My own view is that, if you do a risk analysis, the actual risk is very low. But the consequences of an event - the destruction not only of our comfortable lives and our civilisation but possibly our very species - are so great that it justifies a lot more time and expenditure than we currently give it. We're sticking our heads in the sand, and it's particularly incredible given that we were handed a warning just a few years ago.

Most of us saw the pictures of Shoemaker-Levy splitting into a row of beads and slamming into the "surface" of Jupiter. Most people's response was "how pretty", or "so what?". My response was "S**T! That could have been US!". Why did so few people take the hint? And more to the point, why did not a single news organisation ask - and answer with whizzy computer graphics - the question "what if that happened to earth instead of Jupiter?".

Well the BBC did a few documentaries, but you have to remember that Jupitur is kind of the vacuum cleaner of the solar system. Its high gravity means it sucks up a lot of asteroids and things.

Although personally if the Earth was hit and I and the people I cared about were on it then I wouldn't care that much about the continuation of the species.

actually, it was shoemaker levy 9 which is responsible for the current fuss.

if any of the fragments had hit us, we wouldn't have been here to talk about it. they were all big enough to be dinosaur killers.

The analagy with the toin tossing is misleading. while it is true that being hit by an asteroid is independent of being hit by a different asteroid, the chance of being hit by any asteroid is not independent.

a better analogy woild be playing yatse. you have a number of dice out there being rolled, and sometimes you get a high number and sometimes a low one. when it comes high enough, the dice is removed, and you make the next throw with fewer dice.

the problem with asteroids is that there are so many of them. jupiter does act as a big magnet, pulling things towards it, but if they are far enough away from it it does not collect them.

because we know roughly how big the population of asteroids is, and the range of sizes, we can make fairly accurate statistical predictions of how often they should hit.

when shoemaker levey 9 hit jupiter, jay tate who set up http://www.spaceguarduk.com/ asked the department of defense (he was in the army at the time) what plans were currently in place to deal with the problem.

the answer he got back was basically "why do we need a plan". he found this somewhat shortsighted, so looked into it further.

eventually he found the statistics the government use to decide if they need to spend more money on safety, and this highlighted the problem.

the amount the government spends is determined by the risk multiplied by the consequenses. while the risk of you being hit by an asteroid today are minimal, the risk of someone being hit sometime are a certainty. then you have to factor in the fact that they are likely to have a large number of other victims with them (the entire population of new york or london is not entirely out of the question).

when you do the maths, using the governemts own figures, it tells us how much the government should be spending per year on asteroid defense. the problem is that even lots of years later, we are still not spending this amount.

when you factor in that a lot of the stuff you need to do for this defence will be equally usefull for the manned space program, it then starts to get very interesting.