This is slightly true, though notably the Torino Scale mentions that once an object is classed at level 5, governments may begin to take action to counteract such a collision before it arrives at earth, if the encounter is set to be less than a decade away.

http://en.wikipedia.org/wiki/Torino_Scale

Edit: NASA's JPL maintains the Sentry Risk Table, which tracks all objects that may impact the Earth, with various data points about said objects.

http://neo.jpl.nasa.gov/risk/

The time to initiate an asteroid defense project is long before a threat is even detected.

There needs to be time for technology development, deployment, and testing. Tackling an extinction-level event is not something we want to scramble for at the last possible minute, using untried technology.

Research in this area should have happened since yesterday, but deployment and testing?

The probability of something big hitting us is really low, coupled with the fact that we can see it coming since all objects in space are visible. Miss-calculating a trajectory could indeed happen and we may not notice it if it's coming from the direction of our sun, but the probability of that is even lower.

So why would you spend tons of natural resources, time and money for a machinery of dealing with a problem that we may not have in the next 100,000 years? And what should that machinery do in the meantime?

Personally, I think our world has to solve bigger and more imminent problems that can lead to extinction too ... hunger, disease, overpopulation, economic recessions, natural resources running out, global warming, the destruction of the only habitat we know that can sustain life, nuclear wars and the list of things that can happen in the next 400 years can probably go on. Heck, we came closer to extinction during the Cold War than we ever ever did from a comet passing by and the only thing saving us was the few reasonable men in charge, but we may not get so lucky next time.

> since all objects in space are visible

The majority of objects in space are not visible to us. They only become visible when near and bright enough. Even known comets such as Halley are not visible to us most of the time.

Not with the naked eye as the sunlight reflected by Earth makes that difficult, but we do have deep space telescopes, don't we?

I don't know much on this topic, but if we are able to spot planets that are light years away, then what's the problem with detecting objects that are gonna crash into us in the next 1000 years?

The only problem I can understand is that the sky is a pretty big place, but surely we also have a lot of time to detect such objects.

Planets outside of the solar system are not detected using light from the body itself. They are detected by their gravitational pull on their host star (i.e. tides; causing a slight twinkle in the light emitted by the star), or a transit (eclipse) of the star (causing the star to become slightly dim for a period). In both cases the telescope is looking at stars, and isn't fixated on one star but rather a field of stars, waiting for one to show activity.

Never mind the fact that even if we have a telescope that big, the issue is that these telescopes show a microscopically small field of view. There's a whole sphere that would need to be observed, and repeatedly (since the bodies move).

>The only problem I can understand is that the sky is a pretty big place, but surely we also have a lot of time to detect such objects.

I'm no expert, but as I understand it, the kind of objects we would be worried about are extremely hard to detect as they are dark, cold and relatively tiny.

At the same time, our "eyes" can only look at tiny patches of sky, generally through the distortion of our atmosphere for only a portion of each day with parts of the sky only visible part of the year. Furthermore, we generally have those eyes trained to other, known targets - stars, galaxies, nebulae and all that.

Consider that we didn't spot Apophis [1], which is set to come extremely close, until 2004 even though it's on our lawn [2] in terms of distance.

There is an effort [3] or two [4] afoot related to tracking asteroids and a new DARPA [5] program for tracking our own local junk.

1: http://en.wikipedia.org/wiki/99942_Apophis

2: http://www.howcloseisapophis.com/

3: http://www.skyandtelescope.com/news/160839035.html

4: http://www.planetaryresources.com/mission/

5: http://www.spaceviewnetwork.com/

We detect these planets light years away when they go between us and some light source, or when they change orbit of some light source (thanks to gravity). If the body is cold and the background is black we won't see it until it's close to our sun.

> Tackling an extinction-level event is not something we want to scramble for at the last possible minute

I am not sure if this is in line with Agile principles like YAGNI.

I'm not sure leading humanity should be done according to agile methodology ;)

It's hard to estimate how long it takes for another humanity to develop if we screw it(so we don't know iteration length), and there is the problem of telling them what we did wrong after we were destroyed.

Well, the best defense for something like this is space exploration and collinization. That's being worked on at a reasonable rate.

The big stuff? Sure.

Smaller stuff, from maybe 10kt up to 1Gt (Tunguska was ~15 Mt), though, we can reliably predict its course and evacuate the affected area.

To detect the small stuff at close range, of course, you need to be able to detect the big stuff a ways off. The problem is that massive star surveys are essentially a brand-new thing now that we have Big Data capabilities (we still get a substantial amount of info from scanner photographic plates of the last century). The astronomical community has mostly been focused on producing expensive 1-2 unit runs of a brand new design every decade, each much bigger and better than the last. Survey telescopy, however, is perfectly amenable to economies of scale in large numbers of small scopes, and to the data from a single-purpose survey being used for dozens of different scientific goals.

http://www.fallingstar.com/ , the ATLAS project, is a minimum viable project for this purpose, using small COTS telescopes & sensors to scan the sky rapidly & systematically for objects that have photometric characteristics of something that is headed our way, a few days or a few weeks from Earth.

I see no reason why we shouldn't build twenty of those, scattered around the world, just for immediate situational awareness. We could initiate the project and have it done in six months.

On a longer-term basis, I think rather than constructing things like LSST under the old paradigm, we should be focusing on smaller, 1-2m telescopes (like PAN-STARRS, albeit perhaps without the extraordinary sensors) in very large, economical quantities. Mechanizing the production line is something that's only really been done for much smaller telescopes.

When you have a large, distributed array of automated telescopes, you can sweep the sky quickly and resiliently to weather conditions, or you can turn a portion on a single target that needs a higher signal to noise ratio, for confirming observations, and perform like a much larger telescope's light-gathering ability.

Lastly, there are projects like the Gaia mission that are doing space photometry. While extremely data-starved (better space communications via radio relays & lasers really needs to get here), Gaia would be in an ideal position to detect all the Earth-crossing NEOs that we can't realistically see from the ground due to the sun's glare... if it was at Venus L2 rather than Earth L2, and ideally if there were half a dozen of them instead of one.

The longer out we see it, the better we can deflect it - and our predictive abilities are in the hundreds of years range if we actually bother to spend the money on detection as if it were as important as space toilets on the ISS. The tech is here.

Here is a very early draft of a list of options I've been working on for deflecting asteroids.

http://slant.co/topics/what-is-the-best-way-to-stop-an-aster...

Well, there are actually people working to save the Earth literally. http://b612foundation.org/

That's not true. If we knew for a fact that it would cause global extinction, we would throw everything at it.

We could blow it up with nukes.

We could put a relatively heavy space probe next to it and deflect its course.

When faced with impending doom, optimism and pessimism are both equally fine sentiments. The caveat is that only one of them accurately reflects reality, not that it matters at that point.

I also suppose that industriousness would be helpful for taking one's mind away from the reality of that impending doom.

But hell, nukes to deflect a comet? Sure, we may as well try it -- but I only suggest doing this if we are 100% certain that the comet will both hit us and destroy us. We could conceivably cause our own extinction via a false positive provided by some faulty monitoring device - wait, did that already happen? Nevermind.

If there is a significant chance that a comet will hit and destroy us, it makes sense to do everything we can to prevent it from doing so. Given the stakes, .1% chance should be more than enough for us to take it seriously. It does not seem plausible that we could harm ourselves much by nuking a comet that wasn't going to hit us anyway.

It does seem plausible that we could in fact harm ourselves by attempting to launch a nuclear device out of Earth's orbit. We do have a record of failed launches, several of them recent. Once the nuclear device is out of orbit however, I agree that the harm it can do to us is negligible.

Edit: Also, it just occurred to me the possibility of deflecting a comet (which was never in our path) into our path, instead of away from it, which is really great material for a Hollywood comedy.

Good point, but the chances of a failed launch are fairly small, and the damage from accidentally detonating a large nuke on the Earth's surface, while bad, would be small compared to human extinction.

If we are sufficiently uncertain about the comet's path, we might accidentally deflect it towards us. Obviously, if this is just as likely as deflecting it away from us, it would not be worthwhile to try. But most likely we would be able to reduce the probability of a catastrophic impact even after taking into account the possibility of such an error.

We've intentionally detonated hundreds of nukes in the atmosphere.. Even over heavily populated cities. Sure, it was bad, but not earth-ending bad.

If a lunch failed and "nuked" the launch pad, I hope we'd just move on to another continent and try again (and again)

Nuclear weapons have fallen out of the sky before. No, they won't explode -- it isn't easy to make one go boom.

But I would not be surprised if Green political parties argue that risking a few km^2 contamination is worse than a certain dinosaur killer... :-)

http://en.wikipedia.org/wiki/1966_Palomares_B-52_crash

"The non-nuclear explosives in two of the weapons detonated upon impact with the ground, resulting in the contamination of a 2-square-kilometer (490-acre) (0.78 square mile) area by plutonium. [... another which fell] into the Mediterranean Sea, was recovered intact"

If a billion-ton comet is about to hit our planet, a failed attempt to launch a nuke doesn't matter in the slightest.

It's not Hollywood, it's ballistics.

With early enough detection, even a slight change in it's trajectory can make the asteroid veer off course enough to save earth.

The critical figures here are what the relative speeds are, when the asteroid/comet is detected, what it is made of and how masssive it is.

After you've figured all those out the stage is set and you get a menu:

  - party like it's 2012

  - attempt to deflect it 

  - brace for impact and deal with the aftermath

Any attempt to deflect it has a large degree of uncertainty, including the trouble of getting humanity to pull in one direction for any length of time.

You'd have to develop the vehicle (and the fuel expenses to get the right velocity / direction are going to be terrible, they may be beyond current tech to make a manoeuvre like that, imagine meeting an oncoming bullet by matching speeds and direction where the bullet can come from any direction and you're sitting on a spinning ball), a plan to deflect the mass (by then you'll have burned up a lot of your time budget) and so on.

Maybe, for very small values of maybe.

In context, if we look at the current state of humanity; sure some of our great minds have helped some (not all) of us to live pretty nice lives here on Earth. But on the whole, we're pretty good at screwing up basic things. Non-basic things, like for example having a Mars orbiter not crash into the planet, yeah, we screw those up too.

Anyway, I thought the OPs comment was likely more facetious than anything. Only in Hollywood can we expect a perfect ending.

Um, global melting is happening, and squat is being done about it. I wish I could be as optimistic as you. Maybe because a comet is a thing, a tangible menace, we would emotionally respond.