# Earth-impact events/Discussion
## Background

What have you heard about objects from space striking the Earth? Are you concerned about this? Has the media done a good job of informing the public? --mikeu 13:45, 17 October 2008 (UTC)

## Questions

* Can comets strike the Earth in the next 200 years? If so, which is the probability? Davichito 18:42, 17 October 2008 (UTC)
    Yes, they could. But, most comets are in orbits that do not bring them close to the Earth. So it is much rarer. The closest that one will come to our planet (so far as we currently know) will be P/2000 G1 (LINEAR) on 2016-Mar-22. It will be 12.7 LD at closest, which is much farther than the other "close approaches" talked about in the page. See the list at the NASA/JPL Near Earth Object Program for more detailed and up to date information. The probability of any of the comets in that list colliding with the earth in the next 200 years is extremely small. --mikeu 19:01, 17 October 2008 (UTC)
* In case an asteroid is approaching the Earth and there is a risk of collision, can actual technology be used to deviate the orbit of such object? And how can it be done? Davichito 18:42, 17 October 2008 (UTC)
    There are a number of asteroid deflection strategies that have been proposed for planetary defense. The first step is to identify the objects early enough to allow the many years it would take to implement a plan to modify the orbit. This is often referred to as the Spaceguard program. There has been recent research on the use of a gravitational tractor to deflect asteroids. There is a new Asteroid Deflection Research Center that has been created to develop these technologies. --mikeu 19:37, 17 October 2008 (UTC)
* About comets: There is a novel by Jules Verne: Off on a comet which is about a group of people taken to a comet, by accident. Also, I heard that Europe plans to make a trip to a comet in the next 10 years or so. Is that possible with our current technology? What advantages (scientific/technological/resources) can we get by going to a comet?
    The Rosetta spacecraft was launched in 2004 and will study comet 67P/Churyumov-Gerasimenko when the spacecraft arrives there in 2014. It will release a probe which will land on the comet. The main purpose of the mission is to understand the early history of the solar system, and how it formed. The spacecraft also studied asteroid 2867 Steins on September 5, 2008. --mikeu 20:11, 17 October 2008 (UTC)
* I have recently read a relatively new hypothesis: The Impact And Exit Event, which proposes that the outer planets of our Solar System were created as a direct consequence of a collision between Mars and 'another planet'. Other results of the suggested collisions were that the remnant core of the obliterated planet is now orbiting close to the Sun (Mercury), the resultant accumulation of gases around large gravity wells (Jupiter, Saturn, Uranus) - and the ring systems of each, the creation of the asteriod belt (the rocky remnants of the obliterated planet), the creation of most of the geology of Earth, and the creation of the Moon. The latter two, the hypothesis suggests were caused by another remnant of the Mars collision - an impacting body that collided with Earth. There is no mention of whether the author believes that Earth is at risk of another impact anytime soon. Comets do get a mention - the impact and exit event hypothesis also suggests that comets are the icy remnants of the oceans and atmospheres of the colliding planets that were jettisoned into space following the event, and that they are a natural consequence. An extract from the hypothesis is available: http://www.theimpactandexitevent.com/takla_makan_screenshot.html . I am receptive to the hypothesis, because of what I have subsequently researched. I could do with others taking a look?
    Thanks for the heads up on this hypothesis. Having read the entire content of the impact and exit event (obtained from Amazon) I have a few comments to make. 1) The collation of what is claimed within the book as 'a timeline of interconnected events' is in fact quite plausible. The context within which this 'timeline of events' is placed provides a sense of awareness rarely found in other (dare I say it?) pseudo-scientific publications. 2) The visual evidence used is sometimes difficult to grasp in terms of an overall 'single event' narrative. However, upon further research of my own I have found that imagery is an extremely important element of the hypothesis, so much so that I understand the difficulties involved in expressing the central thread of the hypothesis. 3) Much of the derogatory comments in some areas of the Internet are clearly based upon ignorance of the details stated within the hypothesis, which is unfortunate. Summary: It took a while for the breadth and scope of this hypothesis to formulate in my head, but now that it has I find myself searching - and finding - my own supporting evidence. If nothing else the hypothesis has a strong element of interactivity, which adds to its appeal.
* I have just finished reading the Impact And Exit Event and wonder if this hypothesis has been peer reviewed? It is quite a piece of work but I cannot locate any papers referring to it on the internet (apart from the authors' own website from where I purchased my copy and discussions on a few obscure forums) Regards and thanks.

## Do we have any defense at all against meteors, black holes, etc.?

Note: this section started at
Like, big ones! In all seriousness, if astronomers detected a continent sized meteor headed our way with say, a year's warning, -couldn't we do something? Or if a black hole was heading our way couldn't we use some kind of antimatter type force to push it towards the moon? Or for that matter, if the moon ever broke free (from a black hole?) and started slowly drifting towards us, could we use some greater force to fastly push it away? When our sun expands during it's death throes, how will life forms of that era deal with it?--Dr. Carefree (talk) 09:49, 3 January 2009 (UTC)
    No problem. We have loads of w:asteroid deflection strategies.--Shantavira|$^{feedme}$ 10:15, 3 January 2009 (UTC)
    Um what? Antimatter type force? Our current ability to produce antimatter is very limited and our ability to use it for practical purposes almost non-existant. And I'm not quite certain what the use of pushing a blackhole to the moon is. Plus the concept of us moving a black hole anytime soon, if ever, seem absurd to me. As to what humans will do, billions of years from now if they still exist and live on earth, I don't think many people have given it that serious thought although I'm sure there's something in science fiction Nil Einne (talk) 10:51, 3 January 2009 (UTC)
    In practical terms, not only do we have no defense - we don't truly know what form that defense should take (because we don't know enough about the meteors themselves) and we don't have the ability to detect meteors early enough to make a difference.
    Let's look at those problems individually:
   * Detection: With a large mass on a trajectory that's pointing it at us, the earlier we do something, the easier it is. To take an extreme example: Suppose we only have a few minutes warning...we might have to try to deflect a meteor when it's one earth diameter away from hitting us square-on at the equator...we'd have to bend it's path by 30 degrees to make it miss us instead. To deflect a mountain moving at a thousand miles a second through an angle of 30 degrees in just a few seconds would probably take more energy than we have on the entire planet - it truly can't be done. However, if we know that the meteor is a threat (say) 20 years before it hits us - then the amount of deflection we need is a microscopic fraction of a degree and a really gentle nudge would suffice to save our planet. So early detection - and (most important) accurate orbital parameter determination - is a massive priority both because it gives us time (it might take 5 years to put together a strategy for deflecting this particular rock, building the spacecraft and getting it launched towards it's target) and it reduces the magnitude of our response.
   * Analysis: There are many possible categories of threat. Comets are mostly ice. Meteors come in several varieties - some are essentially solid chunks of metal, others are solid chunks of rock, still others may be loose collections of small bolders, pebbles or even dust. Right now, we don't know which is which - which ones are the most common - whether large, dangerous objects are predominantly of one kind or another. We know (for example) that w:Comet Shoemaker-Levy broke up into a dozen pieces as it descended towards Jupiter - if we'd had to deflect that comet and we'd sent (say) a single large nuclear bomb then a whole range of disasterous possibilities come to mind: (a) The comet might break up before our rocket gets there and we can now only deflect one out of a dozen large, dangerous chunks. (b) Our bomb might actually do nothing more than break up the comet prematurely without deflecting it's course at all. So until we "know our enemy" - we're kinda screwed. We need to send lots of probes out to look in detail at a statistically reasonable collection of comets and meteors - and do lots of science to figure out what's out there.
   * Deflection/Destruction: The problem is that breaking up a large meteor or comet without deflecting it's path doesn't help us. The total damage to the earth from a single rock that's the size of a mountain that weighs a million tonnes is precisely the same as for a million car-sized rocks weighing one tonne each or for a trillion rocks the size of basket balls weighing a few kilograms each. Simply smashing the meteor into pieces doesn't help at all! (The number of movies that get this fact wrong is truly astounding!) So we have to think in terms of deflection - not destruction. If we have enough time (see "Detection" above) then something as simple as a heavy spacecraft that flies along parallel to the course of the meteor for a few years and provides a REALLY subtle gravitational shift - might be enough. That's great because it works just as well with a flying rubble heap as it does for a mountain of nickle-iron or a million tonne dirty snowball. However, getting big, heavy things out of earth orbit and flying as fast as a meteor requires a heck of a lot of fuel and a huge amount of up-front planning. We certainly don't know about these threats early enough to do that reliably. So then we're left with hitting the thing hard with a big bomb, hitting it hard with an 'impactor' or nudging it more gently with rocket motors. None of those things will work for a flying rubble pile. For solid bodies - that'll work. We can build a probe with a rocket motor on it. Make a soft-landing onto the object and start firing our rocket. So long as the object is strong enough to take that pressure without breaking up - or without our rocket sinking into the surface or tilting sideways and deflecting the rock in the wrong direction - that could work. But it's more complicated than that if the object is spinning (as many of them are) - because now the rocket has to fire intermittantly when the rock is at the correct orientation or else the miracle of 'spin stabilisation' (which is what makes bullets fly in a nice straight line) will frustrate our efforts.
    So it's safe to say that right now, we're defenseless on all three levels. Our detection ability is getting slowly better - we have surveyed some of the very largest rocks - and we're tracking their orbits. Perhaps we can now see mountain-sized rocks soon enough - but something a lot smaller than a mountain (like maybe a school-bus-sized rock) can take out a city - and we're nowhere even close to being able to track those soon enough or accurately enough. NASA have sent out probes to several meteors and comets to take a close look at them - and we've even tried firing an 'impactor' at one them...but we have a long way to go. A lot of people are thinking about deflection/destruction strategies...but no governments are building rockets and putting them into storage ready for the day when we'll need them - and funding for the entire process is distinctly lacking.
    At some point we (as a species) need to seriously consider having a colony somewhere away from the Earth. There is always the possibility of the ultimate planet killer coming along that's too fast, too large, too unstable and/or too close to do anything about. Having a colony of humans living on (say) Mars with a self-sufficient life-style and a large enough gene-pool is the ultimate way to ensure the survival of the species come-what-may.
    SteveBaker (talk) 12:43, 3 January 2009 (UTC)
       If you'd like to learn more about it and help create "coursework", there's some activity on Wikiversity at Earth-impact events/Discussion, as well as an opportunity to use your imagination and research skills for colonizing off-planet at Lunar Boom Town. (And SteveBaker: mind if I copy over what you just wrote above? Good detail there!) --SB_Johnny | 12:56, 3 January 2009 (UTC)
          All contributions to the ref desk fall under the w:GFDL - so long as you are using them under those same terms, you are welcome to take whatever you need. SteveBaker (talk) 13:45, 3 January 2009 (UTC)
       Surely it would help to break it up as small objects can be burned up in the earths atmosphere, the amount of mass burned off an object will be proportional to the surface area of the object, which dramatically increases if the object is broken up. To take my point to its logical conclusion, an asteroid of a large given mass would cause significant damage, whereas the same mass of dust colliding with the earth would most likely just flouresce in the atmosphere as it "burned". —Preceding unsigned comment added by 84.92.32.38 (talk) 14:12, 3 January 2009 (UTC)
          The net kinetic energy that has to be absorbed by the Earth system (atmo included) remains exactly the same. While a single large rock would probably cause more damage (at least more localized damage) based on impact, even the distributed vaporization of a massive asteroid would be a catastrophe. A school bus sized rock, sure -- vaporize it. A dino killer? That won't work. — Lomn 14:52, 3 January 2009 (UTC)
             Our main capability in asteroid defense is early warning. Here is an incomplete list of early warning systems that I found:
            * w:Pan-STARRS a (nearly complete) telescope which will continuously survey the sky for asteroid threats
            * w:Near Earth Asteroid Tracking (NEAT) An organization which has several dedicated telescopes for asteroid detection and tracking.
            * w:Spaceguard, a loose affiliation of asteroid detection programs/enthusiasts (including a formal program at NASA).
            * w:Lincoln Near-Earth Asteroid Research (LINEAR) a NASA/USAF/MIT joint project for asteroid detection/tracking
            * w:Lowell Observatory Near-Earth-Object Search (LONEOS) a completed 15-year project which detected hundreds of asteroids.
            * w:Minor Planet Center an organization which is the recognized official center for collecting and publishing orbit data about all known asteroids and comets.
            * w:Catalina Sky Survey another sky survey designed to identify asteroids.
            * w:Spacewatch an University of Arizona program to discover near earth objects.
            * Near Earth Object Program (NEOP) a NASA effort to study the list of known asteroids and determine the impact risk.
             We currently know of around 5500 (see the NEOP page) Near Earth Objects, and hundreds more are being discovered every year. So as you can see, we humans have actually put a fair amount of effort into detecting impact threats from space. No one has ever tested any potential asteroid deflection systems, but as Steve says, early detection is key. --Bmk (talk) 15:44, 3 January 2009 (UTC)
             That doesn't seem quite right... if gazillions of little pieces vaporize in the atmosphere or even hit the earth (somewhat more slowed down by atmospheric friction), they wouldn't also vaporize large amounts of actual earth materials as well (which would cause snowstorms in Havana, etc.). Am I missing something? --SB_Johnny | 15:33, 3 January 2009 (UTC)
                This is little as in much smaller than a mountain, not little as in the size of a pebble. The pieces will still be much too large to burn up in the atmosphere. — DanielLC 19:11, 5 January 2009 (UTC)
(edit conflict)A meteor the size of a continent would be larger than the Moon. The largest asteroid we know of, w:Ceres, is only about 1/4 the diameter of the moon, and it's big enough to be called a w:dwarf planet. There are plenty of other potential risks, for example a rouge star passing through the inner solar system would disrupt the trajectory of many asteroids and comets, flinging some toward Earth. The chances for a large black hole to pass through the solar system are very small, since it would be more massive than the sun but smaller than New York. Small black holes could evaporate to w:Hawking radiation. Remember that the asteroid/comet that probably caused the w:Cretaceous-Tertiary extinction (the one that killed the w:dinosaurs) was only about 15 km (9 miles) in diameter. As for the sun expanding, we could maybe move to Mars, but chances are we won't even survive that long. Most estimates predict there is a "high probability" for us to become extinct within the next three million years or so. Anyway, an asteroid bigger than, say, w:Lake of the Woods, would probably crash through the Earth's crust, exposing its mantle, causing further problems. Anyway, there are plenty of other potential doomsday events that could affect us in the near future (try exitmundi, [warning, popups]), and many of those pose a larger threat to us than the likelihood of an asteroid hitting Earth (which will, with 100% probability, eventually happen). In fact, one potentially catastrophic scenario is already unfolding, and could affect us in our lifetime, yet many are refusing to do anything about it. It's called w:global warming. ~AH1 15:35, 3 January 2009 (UTC)
    The sun won't just slowly expand to engulf the earth - it'll put out huge pulses of hard radiation and do all sorts of other ill-behaved things along the way. There is probably no place in the solar system where we could survive that event. However, the sun blowing up is a fairly predictable event. We can give a fairly accurate prediction as to when that'll happen - and doubtless if our ancestors survive that long - they'll know to a very accurate degree when this is going to happen. So they'd have time to do something to escape to another solar system. The problem with meteors and comets is that they are more random - and the best response is to try to deflect them somehow. We'll certainly have a few thousand or even millions of years notice that the sun is going to give up on us - but we'd be lucky to get 20 years notice of an earth-smasher en route. Black holes are not worth bothering about - there are no big-but-slow ones nearby - and we don't care too much about small ones. Fast-but-big ones are impossible to deal with - if one of those comes by, there is nothing we can do. Meteors and comets are in the middle ground - they DO wipe out entire ecologies (the Dinosaurs - and there was a report out a couple of days ago suggesting that the Clovis people of North America were wiped out by a comet/meteor impact) - and we could do something about it with present-day technology if we put our minds to it. The odds of you or I personally being wiped out by one of these things is tiny - but it's one of the top risks for humanity as a species - so I think we should spend commensurate effort on solving the problem. Global warming should be higher on our list - but comet/meteor protection ought to be up there in the top ten goals of humanity over the next 100 years. SteveBaker (talk) 02:31, 4 January 2009 (UTC)
We have one rock-solid defense against asteroids: Bruce Willis. —Preceding unsigned comment added by 79.122.10.173 (talk) 14:12, 4 January 2009 (UTC)

## Activities

Have you seen a movie or a read a book that depicts a fictional impact event? Did you think that it was realistic? See, and add to, the examples here and describe your thoughts below:
What have you read in the news about asteroid close approaches or impacts? Did the news article provide enough information for you to understand the risks? Recent news coverage of "near misses" are listed here.