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."

Comments

Low priority?

[ajiva]

Not sure about everyone else, but humans as a whole we have many more earth bound issues that require our attention. Famine, disease, and war are way more important, and require more of our attention.

Re:Low priority?

[Klerck]

But how important will famine, disease, and war be when 90% of the population has been wiped out by a massive asteroid and the effects after the collision? I'd say this is far more important.

These problems are insignificant in the grand scheme of things.

Re:Low priority?

[Anonymous Coward]

But how important will famine, disease, and war be when 90% of the population has been wiped out by a massive asteroid and the effects after the collision?

So an asteroid could actually be the solution to these serious problems! I like your thinking.

Re:Low priority?

[Ralph Yarro]

But how important will famine, disease, and war be when 90% of the population has been wiped out by a massive asteroid and the effects after the collision?

War would still be a crucial issue. We cannot allow a mineshaft gap.

Re:Low priority?

[YouHaveSnail]

But how important will famine, disease, and war be when 90% of the population has been wiped out by a massive asteroid and the effects after the collision?

When, or if? It's probably true that a major impact is a near certainty. But what's the time frame for that kind of certainty? 1000 years? 10,000 years?

On the other hand, the probability for significant famine, disease, and war is 100%. That is, those things are all happening, right now. And it seems that there's a very strong chance that these problems will get worse in the near future.

I don't know about you, but I'll take a 0.01% chance that an asteroid will land on my county over a 5% chance that SARS or HIV or some drug resistant bird flu will do me in prematurely.

Re:Low priority?

[Grey Ninja]

When, or if? It's probably true that a major impact is a near certainty. But what's the time frame for that kind of certainty? 1000 years? 10,000 years? I think you forgot to mention that it could also be next year that the earth is hit with a celestial body. Nobody really knows.

But let's assume just for the time being that there's an asteroid due to hit the earth in 10 years that nobody's seen yet. In all likelihood, I think that someone would probably notice when it was a week, or maybe a couple of days away. If no country in the world has a plan to defeat such a threat in place, how much time would it take to come up with an idea, and implement it. Do you think that the object would hit the earth before anything was actually done about it?

Disease, famine, war or the like will probably kill lots of humans in the near future. But I would have to say that fighting those is like fighting smoke. It's coded into our genes that those things will kill us anyway. I say let's spend some time fighting things that we can actually stop. And let's remember that if a plague wipes out 90% of the humans on the planet, then there's a pretty good chance that the earth itself will be ok, along with its biological life. If an asteroid hits the earth, it's not JUST humans.

In a strictly pragmatic viewpoint, I would think that humans being wiped out from the earth would be a good thing, but it would be a small disaster if all life on the planet was destroyed along with us.

Re:Low priority?

[Free_Meson]

When, or if? It's probably true that a major impact is a near certainty. But what's the time frame for that kind of certainty? 1000 years? 10,000 years?

It will happen -- the question is not whether or not an asteroid will hit the earth and whack us back to rats and cockroaches again, the question is whether we'll still be here when it happens, in some shape or form of an organized society. The risk of dying of an asteroid impact is also very small, but because so many people would die as a result of such an impact the risk in terms of total lives is large compared to other, far better funded projects (like earthquake/volcano prediction and mitigation which, in the U.S., costs taxpayers ~$50M per probabilistic death).

On the other hand, the probability for significant famine, disease, and war is 100%. That is, those things are all happening, right now. And it seems that there's a very strong chance that these problems will get worse in the near future.

Great. any ideas on how to address those problems, or will you just use those problems to make an excuse for not addressing a less likely but much more dangerous hazard? An asteroid is far more likely to put an end to the american way of life than famine or disease. A significant thermonuclear exchange could do the job, as could hundreds of years of economic shifts and global warming, but these are problems that don't effect the U.S. and have no tenable solution.

On Famine: A bunch of people live in an environment where it is impossible to grow their own food and they lack the industrial capacity to be able to afford to import food, so they're starving. It sucks. The U.S. does send aide, but this is not a problem that will be solved by spending -- these people either need to die, move, or find a way to feed themselves because spending billions on some sort of global foodstamps program is not a solution to famine -- just like icing down someone with a fever does nothing to help them defeat the infection that is causing the fever, feeding the foodless will only create more foodless while destroying the global market for food. The problem is not, by the way, that there isn't enough food, just that these people can't afford to buy it and/or won't accept american surplus. It's an economic and distributive problem and, while there is no good philosophical reason to let anyone starve, the economic, practical reasons are the ones that keep you (gainfully employed 1st-world citizen) from starving by keeping the farmers employed.

On Disease: People die. tough beans, that's the way it is. Some diseases are horrendous and terrible, and AIDS in Africa and southeast Asia is horrible, but again there is no good solution to the problem and in many cases these diseases are attacking areas already massively overpopulated, undernourished, and poor. Do the poor deserve to live long, fulfilling lives just as much as the rich? Yes. Should the rich be forced to shorten their lives in order to lengthen the lives of the poor? No. This is the choice -- compell pharmaceutical companies to deliver drugs to third world countries at bottom dollar rates only to have a large portion of those drugs, sold at or below cost (with govt subsidies in the latter case) dumped into the profitable markets. What happens then? Nobody gets the drugs because the ROI disappears. We already give free AIDS medications to many patients in africa, for example, but many of those with the disease sell some of their doses back to american individuals and/or continue to have unprotected sex with uninfected individuals, spreading the disease and allowing it to build resistance to our drugs.

Disease is a fact of life, and seeking to somehow eliminate it is an unrealistic goal. Nevertheless, the U.S. spends massive amounts of money on every sort of disease -- I doubt there's a disease out there that a qualified individual couldn't get federal dollars to research. Medicine has advanced a g

Defense from asteroids?

[Anonymous Coward]

Could we eliminate any risk of being hit by an asteroid by reclassifying everything as a planet?

Re:Defense from asteroids?

[Capt'n Hector]

I think I'd much rather be hit by an asteroid than by a planet.

Look Ma, it's raining planets!

Re:Defense from asteroids?

[FattMattP]

Expertly done. There's a job waiting for you in government.

movies

[pvt_medic]

I think one thing that is interesting is how the movie industry already touched upon this. Quite often the movie industry because of their ability to think outside of the box is able to come up with scenarios that ordinarily wouldnt be thought of or addressed. A quite clear example is how the US government after sept 11th hired some movie writers to help look at security holes or lapses that could potentially be exploited. I guess the question remains though are we going to then follow hollywoods ideas on how to address such threats?

Yep.

[Black Parrot]

> 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.

Just like every other problem?

And even then, it isn't so much likely to be "meaningful" as to be "just enough to convince the public we're doing something about it".

Tractor beams

[Amiga Lover]

gravitational tractor beams.

Personally I don't know why this wasn't thought of first before all those silly ideas like just blowing something up

A nice large tractor beam from a high orbiting satellite to repel or attract any asteroid or other thing that's going to hit the planet, and problem solved.

Of course, there's the technical side...

Re:Tractor beams

[Ralp]

Because, blowing things up is not only something we are already very good at, but it's also a lot of fun.

This is a non-story

[tarzan353]

Come on, editors- this is news? We have already researched laser technology, so SDI defense is available. It should only take 2 or 3 turns to equip all of our cities with this technology.

Stick with what works.

[Dr. Bent]

I think we should simply rely on older technology to solve this problem. Don't fix it if it ain't broke...

Famine, Poverty, Disease...

[jim_deane]

None of our earth-borne problems are going to make one whit of difference if an asteroid hits us.

There won't be a welfare problem anymore, because there won't be anyone left to be on welfare.

Jim

Bad idea?

[jaysedai]

Shortly before Carl Sagan died, he wrote an article in Parade Magazine about how he felt this was a bad idea. His premise being that a rouge government or terrorist organization could use technology like this to turn a "near miss" into a direct hit. Which could be potentially far more destructive than a nuke. Obviously he's looking well into the future. But I think he has point.

Re:Bad idea?

[Beryllium Sphere(tm)]

>a rouge government or terrorist organization could use technology like this t

The Soviet Union's collapse discredited Red governments forever, and rouge ones got caught in the riptide too. So there's no need to feel blue about rouge governments, even if you're a Green yourself.

Perspective

[BoldAC]

Risks of dying in car: 1 in 100
Risks of dying in plane:1 in 20,000
Risks of dying from asteroid 1 in 20,000 to 100,000

Source

May I just get somebody to help me pay off my student loans and make sure that there is enough social security to cover my health when I get old?

AC

Re:Perspective

[JoeBaldwin]

I dunno. If your definition of "car" is loose enough to include "convoy of ICBM launchers" then the probability goes significantly higher...

Saving ourselves from famine, disease, war

[handy_vandal]

Famine, disease, and war are way more important, and require more of our attention.

Famine, disesase, and war could all be ended in a moment -- by a sufficiently large asteroid.

Gallows humor aside, I'm sorry to say it but: why should we realistically expect an end to famine, disease, war? They've been with us throughout history. Man has always wished to eliminate these woes -- yes they keep getting worse and worse.

At least there's the possibility that a technological fix might save us from asteroid impact. Give me some reason to believe that there's any kind of fix for war etc.

-kgj

Re:Saving ourselves from famine, disease, war

[useosx]

why should we realistically expect an end to famine, disease, war? They've been with us throughout history. Man has always wished to eliminate these woes -- yes they keep getting worse and worse.

This is an idiotic, self-perpetuating argument. Just because something is, and has been for a long time, does not mean it is an unchangeable truth.

In this particular instance, consider this: the world is rapidly changing and is not the same as, say, during the Roman Empire, yet there is a lot of residual ideologies and beliefs left over from those times. They are not set in stone, however...do not mistake them for "human nature." There have been a lot of improvements to the world that should not be overlooked (civil rights movement, etc).

There are some people who are interested in actualizing change in the world. Some have even written down their thoughts about it.

Re:Saving ourselves from famine, disease, war

[blincoln]

This is an idiotic, self-perpetuating argument.

No more so than the "we should feed the entire planet, cure every disease, and end war before we work on anything else" argument that the original post regurgitated.

That argument is a tar baby - it's designed to attract people in and then get them stuck working on things that haven't been resolved for, what, six thousand years of human society?

Obviously all three of those things are noble goals, but as I've said before, putting other things (like asteroid defence, or space exploration in general) aside until they are taken care of is like me saying "I'm going to wait to have kids until I've got a seven-figure salary, three cars, and a mansion." It could happen, but the probability is so low that it's not worth considering. I will probably be dead of old age before that happens, just like the human race will probably be dead by asteroid impact (or other cause) before we resolve the three issues someone always mentions in this type of discussion.

Geo (or larger) Politics and the human condition

[Space cowboy]

Back in April 2002, the UK government started to fund a centre studying both the near-earth-orbit rocks we know about, and ways of increasing awareness and detection rates, as well as investigating possible protection strategies.

Personally I think it's just playing at people-politics, at least in the form the UK has done it $600k isn't going to go very far, but it's a relatively cheap purchase of public goodwill... On the other hand, at the moment I'll take what we can get.

There's a tiny chance of life as we know it being destroyed. A really tiny chance, and one thing humans aren't good at is disaster-planning - even when the potential result is extinction, the "gut-feeling" is to say "it'll never happen", because none of us have any experience of it happening. This is short-sighted, we should be doing something.

Although I don't think there's any reason to panic about it, the last great ecosystem was destroyed by (perhaps two, perhaps 1) asteroid, as far as we know. Researching, thinking, creating plans would probably be a good idea, at least IMHO.

Simon

A few related sites.....

[Scrab]

http://more.abcnews.go.com/sections/science/DailyN ews/asteroid0107.html

http://personals.galaxyinternet.net/tunga/I7.htm

http://home.att.net/~thehessians/asteroidstrike. ht ml

http://www.sandia.gov/media/comethit.htm

http://www1.tpgi.com.au/users/tps-seti/crater.ht ml

The Tin Foil Hats Say

[Alien54]

As seen in this article featuring the testimony of Dr Carol Rosin. Dr Carol Rosin was the first woman corporate manager of Fairchild Industries and was spokesperson for Wernher Von Braun in the last years of his life. She founded the Institute for Security and Cooperation in Outer Space in Washington DC and has testified before Congress on many occasions about space based weapons. Von Braun revealed to Dr Rosin a plan to justify weapons in spaced based on hoaxing an extraterrestrial threat. She was also present at meetings in the '70s when the scenario for the Gulf War of the '90s was planned.

• As practically a deathbed speech, he educated me about those concepts and who the players were in this game. He gave me the responsibility, since he was dying, of continuing this effort to prevent the weaponization of outer space.

  When Wernher Von Braun was dying of cancer, he asked me to be his spokesperson, to appear on occasions when he was too ill to speak. I did this. What was most interesting to me was a repetitive sentence that he said to me over and over again during the approximately four years that I had the opportunity to work with him.

  He said the strategy that was being used to educate the public and decision makers was to use scare tactics That was how we identify an enemy. The strategy that Wernher Von Braun taught me was that first the Russians are going to be considered to be the enemy. In fact, in 1974, they were the enemy, the identified enemy. We were told that they had "killer satellites". We were told that they were coming to get us and control us-that they were "Commies."

  Then terrorists would be identified, and that was soon to follow. We heard a lot about terrorism. Then we were going to identify third-world country "crazies." We now call them Nations of Concern. But he said that would be the third enemy against whom we would build space-based weapons.

  The next enemy was asteroids. Now, at this point he kind of chuckled the first time he said it.

  Asteroids- against asteroids we are going to build space-based weapons.

  And the funniest one of all was what he called aliens, extraterrestrials. That would be the final scare. And over and over and over during the four years that I knew him and was giving speeches for him, he would bring up that last card.

  "And remember Carol, the last card is the alien card. We are going to have to build space-based weapons against aliens and all of it is a lie."

  I think I was too naive at that time to know the seriousness of the nature of the spin that was being put on the system. And now, the pieces are starting to fall into place. We are building a space-based weapons system on a premise that is a lie, a spin. Wernher Von Braun was trying to hint that to me back in the early 70's and right up until the moment when he died in 1977.

Be sure your Tin Foil hats are well grounded

I'd say it's overblown except

[Daniel Quinlan]

that almost nobody is really taking this seriously, so the lack of interest in space defense seems about right to me. The human species has survived 2 million years without going the way of the dinosaur. It seems like there are many reasons to not stress out about this:

• Low risk/reward ratio, public money is much better spent elsewhere. If someone else wants to spend their money on this, more power to them.
• Our technology is very rapidly advancing, especially relative to the amount of time that passes (on average) between significant asteroid hits. 100 years ago we were completely helpless. 50 years ago, we had nukes, but no missles that were even close to being able to deliver them, in another 50 or 100 years, this may be a yawner due to general technology advances.

To be completely flippant (and yes, I do realize there is a risk, I just think it is relatively low) ... boring! I just hope this doesn't turn into another cause where misguided celebrities drive us into spending money on it disproportionally like certain trendy diseases.

Re:I'd say it's overblown except

[lommer]

I'd agree with you in that money spent developing defense systems is largely wasted, but I do think we need to put MUCH more effort into detection systems. If we can detect an asteroid 10 years before it hits us, I'm pretty confident that it'll get handled. But if we don't even know it's there - we're fucked.

As well, detection systems have other benifits (think advances in optics or radio-imaging, and the discovery of other inner-solarsystem bodies that may be scientifically interesting).

Will they ever learn?

[polemistes]

Just to be pessimistic; I'm sure if anyone ever manage to agree on some way to protect the earth from celestial bodies, it will be in the form of some weapon that is capable of destroying the whole planet before anything else can hit it.

Ruthless men control the weapon's industry, and the weapon's industry controls the money that goes to persuade the desicion makers.

It would be better, at least more senisble, to let the heavenly bodies decide our fate, than these fellows.

Comment removed

[account_deleted]

Comment removed based on user account deletion

Rendezvous with Rama, anyone?

[proverbialcow]

Man, that Arthur C. Clarke is portentious - first we run out of Greek and Roman mythology to name astronomical bodies after, and now we're discussing building a planetary defense against asteroids?

It's all there in "Rendezvous with Rama." Just remember, the Ramans do everything in threes.

Hmmmm...Top Raman...

Need protection against ourselves

[Saeger]

The odds of our civilization being destroyed by asteroid impact in the next few decades is really insignificant when compared to the odds that our advancing technology -- in the hands of still primitive minds -- kills us off first.

It would be a cosmic joke for us to have made it these past hundreds of thousands of slow years, only to be wiped out by a dumb rock in the next ~30 years or so that matter most in our evolution to post-humanity.

--

Famous actors with family attachments

[Operating Thetan]

AFAIK, it's been scientifically proven that they can stop asteroids, although they sometimes die in the attempt. Perhaps a reserve of actors could be established, similar to the national guard?

Re:Famous last words

[Beryllium Sphere(tm)]

A water impact would be far worse than a land impact, according to the people who've tried to make estimates. A land impact would glow white for a long time and radiate much of the impact energy back into space. A water impact would dump much more energy into the atmosphere.

Though realistically, the most damaging place for an Tunguska-sized impact would be in the India-Pakistan area during a crisis, or just about any time in the Middle East. It could easily be mistaken at first for a nuclear explosion. All it would take would be one decision-maker jumping to a conclusion without waiting for the radiation readings, and even a small impact could trigger a horror that would make the twentieth century look good by comparison.

Nerdliness aside...

[bigberk]

I will admit that as a general nerd and space geek (I own a telescope) I am concerned about the possibility of the human population getting wiped out by a large space-borne impact.

But isn't it sad that governments throw billions of dollars towards defense (from other humans) yet nobody is willing to invest in defense of the earth at large?

This is the kind of shit that makes us look awfully silly when the aliens come inspect the rubble after the impact.

Gameplan

[Muttonhead]

Here's the gameplan: control Earth from space. How to do it: pretend to protect against asteroids while developing an offensive strike capability. Explore near earth asteroids. Capture one. Guide it around the sun. Hurl it back to earth and drop it on your enemy. Instant population control.

To those who think money could be better spent...

[Ironsides]

News Flash:
An asteroid has just hit Affrica and wiped out 90% of it's population. (There goes famine.) The impact has also spewed massive ammounts of dust into the atmosphere and Global Tempertures are dropping (so much for global warming) and we are expecting winter to last for several years. () We are expecting most plantlife on the planet to die off due to lack of sunlight from the dust, and a mass extinction of animals from starvation after that. (ah well, no more animals, no more animal rights activists.) Humanity is expected to follow suit being unable to feed enough of it's population due to not being able to grow anything. Wars develope over the remaining food supplies and total anihaltion results, or some survive and we are back in the stone age.


Water Impact:
An ateroid hit the (Pacific/Atlantic, your choice) today causing 1,000 foor (300 meter) tidal waves along the coastlines of all the continents (unless it was in the atlantic, in which Australia is safe). Millions of people were drowned as the water went 10's (100's?) of miles inland causing flooding and destruction of everything in it's path. Need I go on about what a 30' (10 meter) Tsunami can do? Much less one 30 times taller, occuring all over the ocean at once? Entire Islands would go under, possibly entire contries (Carribean, New Zealand, Japan, etc...). The only place that would be safe would be the mountains (Like the Rockies the Andes,and the Alps). Plus what all that water vapor would do.

this whole thing's blown out of proportion

[Anonymous Coward]

You know what's insignificant in the grand scheme of things? The amount of time humans have been on this planet. So far, the earth hasn't been destroyed by a planet-killing meanie, and neither have any of the other planets in our solar system. Assuming we'll be around another 10 or 20 thousand years, do you really think there's that much danger we're going to be hit with something in the next 50 years when we haven't been hit with something in MILLIONS of years?

Jesus H Christ. Leave it to humans to think the world would end as soon as they came into existance. And leave it to their egos to think they could do anything about it.

Umm...

[Jexx Dragon]

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.

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.

Remember basic lessons in probability

[YouHaveSnail]

All these articles about impending doom -- asteroids, earthquakes, pandemics, etc. -- give one the idea that because we've gone a long time without one of these things happening, the chance that we'll have an occurrance is increasing. That shows a basic misunderstanding of probability. If you toss a fair coin and get heads 50 times in a row, the probability of getting heads the next time is still 50%.

We're not 'running out of time' just because we've gone a long time without a major impact. The chance of a major impact this year is exactly the same as it has been in each of the last million years.

Re:You don't understand stats

[jdunn14]

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.

No, YOU don't understand stats

[NoData]

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.

Dual Use Technology

[JGski]

My only concern is that must of what's on the table for "anti-asteroid" technology is, not surprisingly, the same technology being proposed for "US military domination of space". If it weren't for the recent Bush/Rumsfeld/PNAC/Iraq shenanigans I might give the government the benefit of the doubt. However, I'm dubious about this whole concept.

All our eggs in one basket

[Mike_L]

I think that humans should focus on getting off this planet. There are millions of earth-like worlds out there, just waiting for us. As long as we're stuck here on Earth, we have all our eggs in one basket.

Personally, I think that this will happen in my lifetime. With nanotech gaining speed, it won't be long before the first space elevator is built. That technology will facilitate space-based research in biosphere technologies: hydroponics, solar energy, and efficient recycling.

I don't doubt that an asteroid would collide with Earth. Hopefully the inhabitants of the planet won't be at war at the time and will be able to properly respond to the threat and prevent the destruction of humanity's birthplace. But by that time, I imagine humans will be living in hundreds of worlds - still at war with each other, but not vulnerable to a single asteroid.

You assume

[Mateorabi]

You assume that the probability of being hit by an asteroid has a Poisson distribution and is therefore memoryless. In which case you are correct, given that nothing has hit us yet doesn't change the distribution function for the future.

But we don't know what causes asteroids to wander our way, only that it hapens on a semi periodic basis. Perhaps as we orbit the galaxy we come accros regions with more gravitational distortions that are more likely to send stuff hurtling inwards from the oort cloud. Perhaps there is a misterious 10th planet that goes through a dense part of the oort cloud. Perhaps....

Anything that makes the system non-memoryless (i.e. statefull) and makes the events more periodic than random allows us to say that given no events so far, the probability of an event in the near future is greater/has gone up. (Extreme example: We arrive in london at some random time and don't have a watch. The fact that Big Ben hasn't rung in the last 40 minutes allows us to state that it will ring 'soon' with greater certanty than the fact it hasn't rung in the last 10.)

Of couse the fact that an asteroid doesn't hit in just one year makes the already small probability change for the next year only by an infentesmal ammount. I.e. a change of 1/50000000 --> 1/49999999 or even smaller.