Asteroid 2011 AG5: a football-stadium-sized rock to watch carefully

By Phil Plait | March 6, 2012 7:00 am

Over the weekend, I posted about asteroid 2012 DA14, which is not the threat some people are claiming it is (at least not right away). And now I have to tell you about an asteroid that might be a threat in the year 2040. Most likely it won’t be, but it’s something we need to look at carefully.

There’s some background I have to give you so this all makes sense, but let me sum up here: the odds of an impact from asteroid 2011 AG5 are low, but not easily dismissed. If it passes us at just the right distance in 2023, it’ll swing back again and impact the Earth in 2040. We don’t know the orbit of it well enough to say either way just yet, and it may be late 2013 before we can be sure. An asteroid expert at NASA says waiting until next year for more observations is not a problem, but another asteroid expert is saying that waiting that long is a bad idea: we should start analyzing a possible deflection campaign for this rock now. I’m personally leaning toward the idea that getting moving on the initial analysis now is not such a bad idea. If you prefer, I have a list of bullet points at the conclusion of this post with summarized information.

[In the interest of full disclosure: Below, I will be talking about Rusty Schweickart and Don Yeomans. I’ve known Rusty for several years, and Don and I will be on a panel together talking about asteroid impacts at SXSW next week. I honestly like both Rusty and Don. They’re good men, very intelligent and honest, and I have a lot of respect for both of them.

Also, because of the length and nature of this post, I strongly urge everyone to read the whole thing, carefully, before commenting. Thank you.]


The rock

The asteroid, called 2011 AG5, was discovered in early 2011 by a telescopic survey of the sky designed to look for asteroids that can get near the Earth. Although its exact size is unknown, it’s roughly 140 meters across — the size of a football stadium. As you can see from this diagram, it orbits the Sun on an elliptical path that brings it out past the orbit of Mars and inside the orbit of Earth. It circles the Sun once every 1.7 years.

As it happens, the orbit of AG5 brings it close to Earth every few orbits. In 2023, it will pass us at a distance of about 1.6 million km (1 million miles). That’s a safe distance, with no chance of it hitting us at all. However, you have to appreciate the gravity of this upcoming situation.


The keyhole

When AG5 passes us in February 2023, the Earth’s gravity will bend its orbit a little bit, changing the path the rock takes. If it passes close to the Earth the orbit changes a lot; if it’s too far the orbit changes only a little. But if AG5 passes us at just the right distance, the orbit will change just the right amount to put it on a collision course with Earth. This region of space is called a “keyhole”, and in this case, should AG5 slip through it, it will hit us 17 years later, in 2040. That collision, though not global in scope, would be catastrophic: equal to about a 100 megaton explosion, twice that of the largest nuclear weapon ever detonated.

The problem is, we don’t know the orbit of AG5 well enough to know if it will travel through the keyhole or not. As I pointed out in the article about the asteroid 2012 DA14, it can be tricky to try to predict asteroid orbits too far into the future. The orbit of an asteroid is determined by making measurements of its position over time, and because of various effects (like blurring due to our atmosphere) it is impossible to get exactly precise positions. They can be good enough to get an accurate orbit for the next few years, but the farther into the future you look, the fuzzier that path gets.

In the case of AG5 we know its orbit well enough to know for sure it’ll miss us by a million miles in 2023, but we don’t have the accuracy yet to know if it will thread the eye of this keyhole, which is very roughly 360 km (240 miles) across. It’s like standing by the side of a road and knowing a car driving down it will safely miss you by 10 meters, but you can’t be sure if that exact distance will be 10.004 meters or 9.996 meters. And that’s the sort of accuracy we need for AG5.


The odds

At the moment, given the observations we have, the odds of AG5 passing through the keyhole in 2023 are about 1 in 625. For an asteroid impact, that’s actually pretty high as these things go, but still pretty low in realistic terms. Let me be clear: any professional poker player will tell you never to bet on an inside straight, and the odds of getting the card you need in that case are only 1 in 13 or so. The odds of AG5 hitting us are much lower than that!

Moreover, since the orbit of the asteroid is uncertain, as we get better observations the predicted path is likely to change, to move. In that case — which is almost certainly the way things will play out — the predicted orbit will move away from the keyhole and we’ll be safe from a 2040 impact. This sort of thing has happened several times before with asteroids as their positions are observed over time, and the orbital paths clarified.

Still, a 1 in 625 chance is high enough that we need to be sure. So how do we do that?


The mission

As you can see from the diagram at the top of the page, right now AG5 is on the other side of the Sun from us, which means it’s up during the day and impossible to observe. Due to the way the Earth and AG5 orbit the Sun, it was able to be observed in January 2011, but it won’t be visible to us again until September 2013 or so. In other words, we can’t see it at all for another 18 months.

And this is where the story gets interesting.

Don Yeomans, a NASA expert on asteroid detection and orbital prediction, says waiting until the September 2013 observing window is not a problem. On a NASA page about AG5, he said:

It will be an opportunity to observe this space rock and further refine its orbit. Because of the extreme rarity of an impact by a near-Earth asteroid of this size, I fully expect we will be able to significantly reduce or rule out entirely any impact probability for the foreseeable future.

To be clear, this is true. In 2013, more observations can be made, the orbit measurements will be refined, and we’ll probably see that AG5 will miss.

However, while true, Rusty Schweickart doesn’t think that’s enough. He’s a former Apollo astronaut (he flew on Apollo 9) and has been spending the past few years studying the near-Earth asteroid threat in detail. He is part of the B612 Foundation, a group of scientists, engineers, and astronauts who are looking into this threat — trying to determine the best course of action to find, characterize, and (should it be needed) deflect any incoming asteroid.

Schweickart thinks that waiting that long before taking any action is a mistake. If the asteroid is found to be on a path to miss the keyhole, then fine. But if the observations indicate a keyhole pass is likely, we’ll have wasted 18 months that could have been spent looking into the planning of a deflection mission. And given the non-zero odds of such a pass, he thinks that planning should get started now.


The letter

He feels strongly enough about this that he wrote an open letter (PDF) to the NASA Chief Administrator Charles Bolden, himself a former astronaut. In this letter, he urges NASA to start looking into a pair of missions that can not only deflect the asteroid should it be found to be a significant impact threat, but can also carefully observe it in situ to make sure that the asteroid is moved onto a path that keeps it safely away from Earth.

Schweickart’s idea is that a mission to deflect the asteroid needs two parts: 1) what’s called a kinetic impactor, to ram the asteroid at high speed and push it into a different, safe orbit, and 2) an observer spacecraft that is placed into position near the asteroid at an earlier time, to carefully measure the asteroid’s position and report back on the effectiveness of the impactor. What he is asking for in his open letter is not that this mission be built, just that NASA start looking into what would be needed to design it should AG5 prove to have better odds of being a threat.

As Schweickart told me in a phone conversation, observations from the ground after a deflecting impact from a spacecraft will not be sufficient to determine if the asteroid is on a safe orbit or not. Therefore, including an observer spacecraft is critical.

There’s an added benefit too: the observer can be outfitted in such a way that should the impactor not get the whole job done, the observer might be put to use. While the mass of the observer spacecraft is small, it still has gravity. If it is equipped with low-thrust ion engines (which have been used in such spacecraft as Dawn and Deep Space 1), its feeble gravity can be used to very slowly alter the asteroid’s orbit, in much the same way Earth’s much stronger gravity can bend the path of the asteroid (see the illustration at the top of this post). Using the observer as a “gravity tractor” takes a lot of time — years, certainly — so again, the sooner something gets done the better.


The reaction

NASA’s reaction to this has yet to be seen. However, this was not Schweickart’s first letter to NASA: a few months ago he sent an initial letter to NASA about the asteroid, asking them to immediately begin a mission analysis. The answer he got was interesting. Basically, the argument was that the delay until September 2013 is warranted, because NASA has experience with a mission like this: the Deep Impact spacecraft was sent to comet Tempel 1 back in 2005. Deep Impact was equipped with a block of copper that was released and slammed into the comet, while the main spacecraft observed the impact from a distance. The experience gained from this mission means that a new mission for AG5 already has a precedent.

It was this reaction by NASA that prompted Schweickart to send his second letter. He argues that the Deep Impact mission analogy is not a good one for AG5. For one thing, Deep Impact was an all-in-one mission, with an observer and impactor on board one spacecraft. A campaign to deflect AG5 will require two separate spacecraft, and two launches (to make sure the observer is in place before the impactor’s job gets done). Moreover, Tempel 1 is 1800 times bigger than AG5, which made it a much easier target to hit. Not only that, a kinetic impactor to move AG5 would have to hit at a much higher speed than the Deep Impact probe did (13.7 km/sec versus 10.3 for DI). And not only that, but the mass of the AG5 impactor will have to be much larger than what was used for Deep Impact — the DI mission wasn’t meant to deflect an comet, only to hit it and excavate a crater. To significantly deflect even a smaller rock means using a much heavier bullet.

The best time to deflect an asteroid is before it enters the keyhole. The keyhole is 360 kilometers across, so only a relatively small change in the asteroid’s path is needed to miss it. But once AG5 passes through the keyhole (if it does), then it has to miss the entire Earth! Instead of it missing a target 360 km across, it has to miss a planet 13,000 km across. That usually requires a much larger change in velocity. Either way, hitting it earlier is better.

Schweickart also points out that the size of the asteroid is not really known. All we have is an estimate based on its brightness and distance. If it’s even 30% wider than we think that means its mass increases by a factor of 2. That in turn means moving it is twice as hard.

Because of these difficulties, Schweickart is convinced mission planning needs to start now. He got a preliminary report from a European group called Deimos which investigated what missions might be possible to deflect AG5. According to that report, missions to AG5 are very difficult with existing launch vehicles (though easier if SpaceX gets its proposed Falcon Heavy rocket flying soon), and timing is a serious issue.


Deep Impact, Part 2?

And this is where things get sticky. The Deimos report is not an actual mission analysis plan, more like an outline of why we need to do one. It’s very interesting and a good motivator, but not necessarily enough to get NASA moving on this. Many of the arguments presented by Schweickart have been countered by NASA as well.

For example, Schweickart and Deimos assumed a change in the velocity of the asteroid of 2 cm/sec is needed. However, in some cases that may be an overestimate. To miss the keyhole, the rock’s velocity need only be changed by a fraction of a centimeter per second, if the spacecraft kinetic impact were to occur a year or two before the keyhole pass. After the keyhole pass, yes, a larger velocity is needed because the Earth is a larger target, as described above.

That small change in velocity could be performed much more easily, with some time to spare. It’s even possible it could be done with a Deep Impact type spacecraft, which we know worked.

Schweickart points out the difficulties with this type of mission (speed and size of the target, as well as lighting on the Deep Impact mission being better than what an AG5 impact would have to deal with). However, there are some things that would be easier for an AG5 kinetic impactor than for the original Deep Impact comet mission. Comets are surrounded by material sublimating (turning from a solid to a gas) from the surface. That fog makes "terminal guidance" — last minute steering — difficult. But the asteroid AG5 won’t have that. Also, that material pushes on the comet, making its orbit difficult to determine months in advance, making a rendezvous harder. Again, AG5 won’t have that, which should make getting there somewhat easier.

Yeomans also argues against the need of an observer spacecraft, saying ground-based observing should be able to tell whether or not the kinetic impactor worked or not. Schweickart strongly disagrees, claiming that the observer craft is critical as well to make sure (and also to use as a gravity tug). I honestly do not have enough information to be able to say who is correct in this case.

Clearly, there’s a lot of back-and-forth here. When all is said and done, the argument really boils down to two things: should we be looking into a mission right now, and if we do, what kind should it be? In a nutshell, Yeomans thinks we can wait until after the September 2013 observations to see if we need to think about a mission, and Schweickart thinks we should be planning it now.

When phrased this way, I lean toward looking into a mission (and then if we need one, what kind to do based on what’s found in the analysis). That way if the time comes and we need it, we’re that far ahead of the game. It doesn’t cost much: we’re not talking about cutting metal for a spacecraft, or even designing one. All Schweickart wants is for NASA to do the launch and mission analysis. And while it seems likely that AG5 will miss the keyhole, why take the chance when the stakes are so large, and the effort so little? Better safe than sorry.


Conclusion

In case anyone scrolls past all that stuff above and just wants to get the bullet points, then here you go:

  • Asteroid 2011 AG5 is a 140 meter wide rock that will pass a million miles from Earth in 2023. If it passes at just the right distance — through what’s called a keyhole — the Earth’s gravity will bend the orbit of the rock just the right amount to put it on an impact course for 2040.
  • The odds of AG5 going through the keyhole are right now measured to be about 1 in 625. Further observations should refine its orbit, and from experience and physics, most astronomers think those odds will drop to 0.
  • However, we cannot be sure that will be the case, and the current odds, while low, are still high enough to take seriously. The problem: due to the orbit of the asteroid, more observations won’t be possible until September 2013. Waiting that long means delaying any potential space mission to deflect AG5.
  • A campaign to deflect the asteroid optimally uses (at least) two missions: one which arrives at the asteroid first to observe, and a second to slam into the asteroid as hard as possible, in an attempt to change its course. According to Rusty Schweickart, the observer spacecraft is critical to make sure the impact did its job, and can also be used if needed to finesse the asteroid into a safe orbit.
  • Such a campaign can be planned — launch windows determined, spacecraft impactors modeled, and so on — relatively quickly and cheaply. Schweickart is imploring NASA to start an analysis immediately. No actual mission needs to be proposed as yet, but should September 2013 followup observations of AG5 not eliminate the possibility of impact, then starting a campaign analysis now means we’re that much readier should the time come.
  • A call to action by Schweickart in an initial letter to NASA was declined. Officials there said the Deep Impact mission gave them the experience needed to put together a mission should AG5 prove to be a real threat. Schweickart wrote a second letter, saying this was not the case; a campaign to deflect AG5 is more complicated and more difficult, and analysis should begin now.
  • The decision is now in NASA’s hands.

Let me be very clear: Rusty Schweickart is not some crackpot; he is an accomplished astronaut and even served as Co-Chair of the NASA Advisory Council Ad-Hoc Task Force on Planetary Defense. Nor do I think Don Yeomans and NASA are simply dismissing his case out of hand; they have obviously given this quite a bit of thought and believe their case that waiting for more observations is sufficient.

Who’s right?

In my personal opinion, it’s very likely that NASA is correct that observations to be made late next year will refine the orbit of the asteroid, and we’ll find it will miss.

However, Schweickart appears to be correct that there is no reason for NASA not to analyze the AG5 case in more detail. If AG5 turns out not to be a threat, no harm done.

And if it does turn out to be on a collision course with Earth, then perhaps much harm prevented.

Image credits: Dan Durda; NASA; Wikipedia

 


Related Posts:

No, asteroid 2012 DA14 will not hit us next year
Followup: Deep Impact crater on Tempel 1
Debunking Doomsday
My asteroid impact talk is now on TED!

 

Comments (117)

  1. Ryan the Biologist

    Yeah, I’ve been keeping an eye on that particular rock on JPL’s near-earth object site for a while now, along with 2007 VK184 which is also a little on the almost-scary side. I can tell you that impact risk table they have on there is not healthy for paranoids like myself :)

  2. cy

    Phil this asteroid has been in this orbit for millions of years if not longer correct? If it comes close every few orbits then its come “close” to earth (say within a few million miles) probably at least 10,000 times. Still hasn’t hit us yet.

    I’m not trying to come across as dismissing it but I’m more worried about the Tunguska size rock that we discover 36 hours before it hits Earth because its small enough to avoid detection but big enough to destroy Paris which I believe is where every asteroid strikes… ;)

  3. Messier Tidy Upper

    However, Schweikart appears to be correct that there is no [??? – ed] for NASA not to analyze the AG5 case in more detail.

    I think there’s word missing there right? Reason perhaps?

    Although its exact size is unknown, it’s roughly 140 meters across — the size of a football stadium.

    How does that compare with the size of cricket oval, BA? ;-)

    Schweikart thinks that waiting that long before taking any action is a mistake. If the asteroid is found to be on a path to miss the keyhole, then fine. But if the observations indicate a keyhole pass is likely, we’ll have wasted 18 months that could have been spent looking into the planning of a deflection mission. And given the non-zero odds of such a pass, he thinks that planning should get started now.

    I fully agree with Schweikart on that. This asteroid is very unlikley tohit us -625:1 are good odds of a near miss in 20409 s well as now and there’s certainly no cause for panic but it also makes very good sense to plan just in case – and if not for this asteroid specifically then for others later that may be of more concern.

    BTW. Wonder what the odds of 2011 AG5 hitting Mars are? It also crosses the red planet’s orbit too I see.

    PS. Any chance of it – and 2012 DA14 – recieving proper names at some point soon~ish?

  4. Dave Scott

    Could you spell Rusty’s last name correctly please? it has a C in it.

  5. Matt Higgins

    How much, if anything, does a launch and mission analysis typically cost? If it’s not prohibitive, I guess I just don’t see why NASA would sit on its hands on this. Better to have done the work and not need it (yet) than not do it and have to rush it once the keyhole is threaded.

  6. Titan

    Very nice writeup. I tend to agree with Schweikart because it seems foolish to not at least have some kind of rudimentary plan drawn up in a file somewhere that can be pulled out if we need it. I would rather have the research done beforehand so that the engineers can simply execute the plan on a moment’s notice. Like you said, it is a simple mission as far as space missions go. A high mass impactor and standard guidance and control. Something could probably be cooked up in a matter of months if there was a dire need.

    How much would it cost NASA to get a couple of scientists and engineers together for a week to hammer out the math and logistics of this mission? Almost nothing, especially since those individuals are likely already NASA employees to begin with.

  7. Nigel Depledge

    MTU (3) said:

    I think there’s word missing there right?

    I think there’s both a word and a punctuation mark missing there, right?

    ;-)

    Sorry, but you set that one up so well, I couldn’t resist taking the shot.

  8. Nigel Depledge

    Here’s another possibility that you did not mention (although maybe Schweikart and / or Yeomans did consider it) –

    What if the asteroid is a rubble pile rather than a solid object? If the former, an impactor is going to have far less – heh – impact than in the latter case.

  9. Rob

    @ cy #2:

    Gambler’s Fallacy. “I just rolled dice nine times and got snake eyes every time. Must mean I’m going to get snake eyes next roll, right?”

    Phil, I think there is another very good argument for doing this initial analysis now: We WILL need to do it at some point for some object. If (and most likely when) the impact is ruled out for AG5, the discussion and ideas and calculations and report don’t all evaporate. It will be filed away, ready to be used next year, 4 years from now, 20 years from now, 4 centuries from now, when another one of these objects is finally determined to need ‘orbital remediation”.

  10. Ross

    Why not *just* a gravity tractor/tug? Why also the impactor? The tug works regardless of whether it is a solid object or a rubble pile. Do we think we cannot launch a massive-enough tug? Or do we think a tug alone will not get the job done in the relatively short time remaining?

  11. I wonder how many evangelicals are convinced that GOD would intervene.

  12. kevbo

    So, most of these orbit diagrams imply that everything is on the same plane (unlike Pluto, for example). How true is that (or is there also a good chance of this thing missing us ‘high’ or ‘low’?

    and @8 Chuck: you got it backwards – don’t you realize that an asteroid impact would be just punishment for all the gays in New Orleans?

  13. Dave

    Very nice article! I agree with your intuition, Phil, that to start minimal preparations is prudent.

    Just to clarify one thing — chances are roughly 624/625 that, with more observations, the probability of impact will drop to near zero, and roughly 1/625 that the probability will increase to near one.

  14. Jason

    I agree that plans probably should be drawn up, rather than waiting until we know for sure. Plus, it’s not as if those plans would be wasted if this asteroid poses no threat. 18 months of work drawing up potential deflection scenarios will come in handy if (or more accurately, when) another similar asteroid is found that poses a danger.

  15. Rim

    Meh, we should make for the moon to increase our odds of one of our colonies not being hit to 100%.

  16. kwoolf

    Very interesting article with PP standard solid writing and reasoning. One question that occured to me is what does the theoretical orbital perturbation by impactor do to the chances of future earth impacts past 2040?

  17. thetentman

    I’ll be 82, “bring it on” to quote one of our great Presidents……..Uh, Oh wait a minute………….

  18. Hey, I posted a link about this on that original post. No “tip of the restraining order” or anything for me? ;)

    http://larianlequella.blogspot.com/2012/03/everybody-panic-were-about-to-die-or.html

  19. @5. Nigel Depledge :

    MTU (3)
    I think there’s both a word and a punctuation mark missing there, right? ;-)
    Sorry, but you set that one up so well, I couldn’t resist taking the shot.

    Fair enough.

    Mea culpa. Yes, I’m a terrible typer and it’s Murphy’s law that in a comment noting an error of the BA’s I made about five (if not more) of my own. Sigh. I should’ve used the editing time more wisely but I got distracted instead. D’oh! :-(

    @9. kevbo :

    .. @8 Chuck: you got it backwards – don’t you realize that an asteroid impact would be just punishment for all the gays in New Orleans?”

    But then it probably won’t hit New Orleans will it? Now what would they say if it landed on Rick Santorum during one of his rallies or Pat Robertson’s house or Kent Hovind’s jail*, I wonder? ;-)

    * Click on my name for one source of info on that.

  20. llewelly

    What I cannot believe is how blind both NASA and Schweikart are. They are missing out on a golden opportunity! Any idiot can see that not only does this asteroid sometimes pass close to Earth, it also occasionally passes close to Mars!

    After all the decades people have spent trying to find a way to get to Mars, it is amazing that such smart people should entirely fail to see the implications of an asteroid, which will take us elliptically to Mars, falling into our laps!

    Rather than agonizing over whether or not it will hit us (unlikely), we should planning to colonize it as soon as it arrives. Then, when the asteroid makes its next close approach to Mars, we can colonize Mars!

    Percival Lowell, honored astronomer of the great clear-skied state of Arizona, would spin in his grave if we shirked this opportunity.

  21. Chuck Anziulewicz (#8):

    I wonder how many evangelicals are convinced that GOD would intervene.

    ITYM “convinced that G-D is the one who put it on a collision course with the Earth in the first place, but given us enough time to ‘repent’, and have it miss the keyhole”.

    On the other hand, my first impression when I saw the top of this article was “Uh oh, Space Hippo has returned!”

  22. jeremy.greenwood

    Why not just nuke it? I know the arguments about converting 1 big impact into a lot of moderate impacts, which may well be worse; and that a loosely constructed body might absorb most of the force and not move very far.
    But, I would value some amplification on these objections.
    Surely, in theory, if the object was smashed into pea sized pieces we would suffer no more than a glorious meteor display (albeit radioactive). I doubt such fine fragmentation would happen in practice, but would not smaller pieces (hopefully not many of a dangerous size) be easier to move out of the way?
    With regard to the second objection, a football stadium is surely rather small in the face of a nuke, so could we not expect a significant change of orbit, especially if performed early?

  23. James H. (south of Dallas)

    It’s better to err on the side of caution. Begin the studies now, and if it turns out they aren’t needed in this case, they probably will be in the future, and you have your headstart.

  24. Tom Hail

    #2 cy I doubt this rock has been in this orbit for millions of years, not with it crossing both Mars and Earth’s orbits.

  25. ragnar

    @ cy #2,

    I’m pretty sure that if the asteroid hits Paris, even most French won’t mind either.

  26. David Pugh

    Do we have any assets in orbit that could more accurately measure the orbits of potential impactors and, if not, what would it take? Would two different orbiting telescopes provide a large enough baseline to accurately locate an asteroid using parallax?

    Given that there are lots of potential impactors out there, it would seem to be better to improve our threat analysis in general before concentrating on a specific threat.

  27. Zaphod

    Why just pester NASA? If they’re not interested then get ESA, the Chinese and the Russians involved. This seems to be a global issue, it could hit anywhere, and the USA is by no means the only nation capable. In fact, Americans can’t even get to the ISS unaided!

  28. Tim

    @ #3 – How does that compare with the size of cricket oval, BA?

    Lords (ENG) Cricket Ground is ~230 meters, making it impervious to meteor strikes. Wembley (ENG), an actual Football stadium, is easily double that of your average American Football stadium and while it is also impervious to meteor strike it is highly susceptible to a miserable performance and uninterested crowds.

  29. Michael

    “Let me be clear: any professional poker player will tell you never to bet on an inside straight, and the odds of getting the card you need in that case are only 1 in 13 or so. The odds of AG5 hitting us are much lower than that!”

    True, but the stakes are much higher. Beating the odds in a poker game usually doesn’t detonate a 100 megaton bomb. Then again, I’ve not played very many high-stakes poker games…

  30. ctj

    i’m surprised to see a kinetic impactor as the focus of the plan. after all, “bad universe” demonstrated why a KI is not the best approach for deflecting asteroids.

    if we’d be sending an observation craft, and could ostensibly use that craft as a gravity tug, could it be more effective to land that craft gently on the surface and use the ion engine to push the asteroid? since 2011 ag5 is so small, the craft’s thrusters should be sufficient to reposition itself if it lands in a spot where its engine spins but does not push the asteroid (by the way, the spin issue could affect a KI if it hits off-center). since it’s not destroyed, the “pusher” could do double duty as its own observer, to allow for course corrections.

  31. JeffJW

    Why not use this opportunity to generate a proof of concept. A mission to move this asteroid’s orbit could be put together, launched, and attempted even if if the odds fall to zero upon further observation. I know there’s a huge cost related to this idea but since this is something that hasn’t actually been done before, attempting it when there’s no pressure seems like a great opportunity to learn something so when it absolutely has to be done, the odds of success are greater. Taking the opportunity of the close pass in 2023 could generate a tremendous amount of data that can be used for future planning.

  32. David K

    I would provide the following suggested clarification of the odds: The chance of the asteroid passing through the keyhole is low enough that I would not bet on it happening, but the chance is high enough and the consequences are sufficiently dire to justify buying insurance against it.

    The only point I have a misgiving about is that, with insufficient knowledge of where the asteroid actually is going to pass, we are as likely to move an asteroid that would miss the keyhole into the keyhole as we are to move an asteroid that would hit the keyhole away from it — and we really do not want to invest in such a crapshoot.

  33. Kappy

    Maybe I’m missing something here, but if it turns out that the asteroid WILL in fact pass through the keyhole, why would we have to do something now? If we find that it does indeed pass through the keyhole in 2023, we would still have from 18 months from now (mid-late 2013) until sometime near 2040 to do something. Isn’t it likely that we will have much better tech by then to move the asteroid at lower cost or more efficiently / safer? I realize if we go the gravitational tractor route it may take a while to alter the course, but will it really take longer than a decade? Two decades?

    -kap

  34. Justin

    With AG5 on the other side of the sun, that only seems to prohibit -ground based- observations. Why can’t we use space based telescopes? If it is still too close to the sun (visually), use the Earth or Moon as a shade (although I admit that due to the moving nature of orbits, it would be a quite short term window).

  35. Peter L

    Thanks for the article Phil!

  36. Calli Arcale

    Interesting arguments on both sides; the only reason I can see for NASA to *not* do the study right now is that they’re under considerable budget and schedule pressure at the moment, which frankly is a pretty sad reason. Too many good missions are being cancelled or threatened; I could understand a space center being resistant to taking on additional work under that environment.

    But Schweikart is right. It is better to start sooner rather than later, and honestly, we should be working on this already. 2011 AG5 might not get us, but somewhere out there, there is probably an asteroid with our name on it. It would be good to be prepared.

  37. TerryS.

    Schweickart is not only a member of the B612 Foundation, he is the founder and current Chairman of the Board. Seems like a little bit of self-promotion here.

  38. Jay

    How come we don’t have a fleet of rockets/sensors available whose sole job is to be able to “cheaply, quickly” survey these things?

    Rockets that can be launched within 3-6 months with a standardized 100 pound payload consisting of telescope, camera, radar, that can intercept, possibly match orbits, possibly land a navigational beacon on the object.

    How come we don’t have a longer term satellite in an L-5 position able to be an additional set of eyes and ears?

  39. Timothy from Boulder

    “Moreover, since the orbit of the asteroid is uncertain, as we get better observations the predicted path is likely to change, to move. In that case — which is almost certainly the way things will play out — the predicted orbit will move away from the keyhole and we’ll be safe from a 2040 impact. ”

    In general, the trend for orbital impacts is that continued and improved observations result in progressively *higher* probabilities of impact as the uncertainty region shrinks in size, followed by a sharp decrease when the uncertainty region no longer includes the Earth (see diagram at http://upload.wikimedia.org/wikipedia/commons/thumb/0/0c/Apophis_ellipse.svg/250px-Apophis_ellipse.svg.png)

    This may not be the case with AG5 since the next observation is 18 months away and the next observation may exclude an impact altogether. But if the Earth (or rather, the keyhole) is still in AG5’s path for that observation, it is to be expected that the probability of impact will be *higher* than 1 in 625.

  40. “Let me be clear: any professional poker player will tell you never to bet on an inside straight, and the odds of getting the card you need in that case are only 1 in 13 or so.”

    Depends on the game. But, since you already have some cards and there’s cards out a gutshot is less than 1 in 13 and the real important statistic is whether the odds that you get your hand are better than the pot odds. If calling is less than 1/13th of the pot you should call that bet. If the person might fold, you might even semibluff that hand. Such that if they fold you win, and if they call you have reasonable outs, and the combined odds of those are such that you’re getting better odds from the pot than you’re putting in.

    Never is a strong word.

  41. @Messier Tidy Upper #3

    Any chance of it – and 2012 DA14 – recieving proper names at some point soon~ish?

    Nope. Before an asteroid can receive a name it must first receive a permanent designation number. In order for an asteroid to receive a number (currently these two objects only have provisional designations) it needs to have been observed during at least 2 oppositions, or as many as are needed for a reliable orbit to be determined.

    Once a designation number is assigned, the asteroid’s discoverer has 10 years during which to propose a name for it. Once a name is proposed to the IAU’s Committee for Small-Body Nomenclature, it is reviewed and, if approved, is published in the Minor Planet Circulars and made official.

    If you’re still awake and want more info on asteroid naming conventions (yes, there are rules), click here.

    —Dr JL Galache
    Minor Planet Center

  42. DG

    I like the idea of the proof of concept.

    Other than that, I have to agree with the wait and see option. The target doesn’t magically go from a keyhole to 8000 miles across. It gradually gets bigger from keyhole size to 8000 miles over the course of 17 years. E.g., the keyhole at it’s closest point may be 240 miles across. 6 months before that the keyhole might be 100 miles across. It’s either already on target or it’s not. We just don’t know.

    Other than a proof of concept, we’d just be spinning our wheels. And if we need that 18 months on top of 17 years to divert it we deserve to be obliterated! Over 40 years ago we put people on the moon in under 10 years of work, and we didn’t have 1/10th of the technology we have now. If you really think that 18 months would make a difference, then you should be arguing for starting to build ships now, and send more than two just in case. :)

  43. Greg

    Capture the asteroid into Earth orbit and use it as a space station.

    Deflecting that asteroid requires probably the same kind of technology that could be used for a capture, so why not do both for the price of 1 mission?

  44. Keith Hearn

    Phil, great article, nicely balanced, and very informative.

    kevbo@12: On most of these orbital diagrams, if an orbit is shown in two different shades, like the light and dark blue in this one, the colors indicate when it is above or below the plane of the ecliptic or Earth’s orbit. I think light color means above the plane, but I’m not sure about that (but it doesn’t matter much for our purposes). You can see that Mars’ orbit is also light and dark, since it’s not exactly on the same plane as Earth’s.

    So 2011AG5 crosses the plane right as it passes Earth’s orbit, then crosses the plane again somewhere outside of Mars’ orbit. That crossing right at Earth’s orbit is what makes it dangerous.

    It’s not a danger to Mars, since it is well above or below Mars at that distance from the sun. Plus, based on the colors, we can also see that Mars is on the other side of the plane at both places where the asteroid crosses Mars’ orbit, so it’s a clear miss both times.

    jeremy.greenwood@23: A nuke doesn’t really have all that much energy compared to an object moving at orbital velocities (which is why asteroid impacts are so dangerous). Plus, there are political issues involved in putting a nuke into space, like the Outer Space Treaty of 1967, which forbids them. While it would probably be possible to get around it for this kind of purpose, it’s a lot easier politically to just use an impactor or tractor. And it’s not up to NASA to decide to break an international treaty.

    Plus there’s the issue that nukes in a vacuum don’t create blast waves to push anything, so you’d still have to detonate it in contact with the asteroid.

    David K@33: By the time we’d actually be trying to move it, we’ll have much more data on its orbit and we can make sure we push it in the right direction.

  45. I wrote my little (and much less detailed) take on the threat of this asteroid here:
    http://linasc.net/2012/03/01/asteroid-to-hit-earth-%e2%80%93-or/
    I am happy to see I was right.

    Great post, Phil! I love the expertise and the details you bring to the subject. Everybody getting scared about astroids ought to read your blog for a reality check.

  46. Miguel

    So if we push it out of the way now, what happens to future orbits? Did we change the odds off it hitting us on future passes?!

  47. Phil:
    Perhaps you could put in for a radar session with Arecibo & the GBT. Then observations can happen right now, no waiting…

  48. David M.

    Ya think an 82 yr. young guy (by that time) will still have political correctness on FauxNews?

  49. Bryan McCloskey

    @David Pugh: That’s what I was thinking — could some other platform be used to make observations before 2013? Kepler, or one of the SOHO-type missions, etc.?

    Alternatively, could we find unnoticed images of the rock in older legacy images and calculate a better orbit from those?

  50. Bill

    Odds of making an inside straight are 12 to 1. 4 cards work out of the 48 you have not seen.

    Good article.

  51. Push it into Mars!

  52. CB

    @ Kappy #34

    As Phil explained, if we wait until after it passes through the keyhole to try to divert it then we’ve just made the problem many times more difficult since now we have to divert the asteroid enough to miss the entire planet, not just the 360km wide keyhole.

    Look at the past 50 years of space technology development. Are you really willing to bet that it will advance enough in the next 20 that moving an asteroid will be a thousand times easier for us after 2023 than before? Because it would have to be to make it worth waiting.

    And in any case such a mission will take a long time to plan, develop, and execute. And then the mission might fail. Which means it’s doubly important to do it early.

  53. Wzrd1

    @23. jeremy.greenwood, which is worse, getting shot by a 12 gauge shotgun with 00 buckshot or being shot with a 12 gauge shotgun with a rifled slug?
    That is what is wrong with trying to shatter it. IF it would shatter.
    If you have a desperate need to use a nuke, I’d go for a near miss and let radiation pressure do some pushing, but it won’t make THAT big a difference in velocity of anything with significant mass.

    One problem with making a mission analysis now is, what is the actual size, mass and density? As was mentioned by one above, if it’s a rubble ball, an impactor just gets absorbed with minimal change in velocity. Now, a general purpose, high mass bird with a high mass impactor so that the heavy bird acts as a backup tug that could tug it further out of the way would be a worthwhile mission to analyze. As I said massive, that obviously means it’d have to be assembled in orbit. It need not be fancy assembly, I DO believe we can dock spacecraft together still and still fire engines, unless we’ve suddenly forgotten how to do that (if so, the ISS is SOL). :)
    The mass of the vehicle need not be fancy either, simple ballast of anything with decent mass, as we’re not making a study, but redirecting it.
    Of course, I’d also want to look into the practicality of eventually tugging the thing into a high orbit for study and possible mining… ;)

  54. @ #44 – You can do radar in the daytime, but not at long range. It has an inverse
    fourth power of the distance on the signal: inverse square out and inverse square back.
    So 2011 AG5 is too far away now. But radar data may be taken in 2013, although the
    closest approach is just under 1 AU.

  55. I wonder, how useful would a mission analysis be as a format/tool for preparing for OTHER missions like this? Even if AG5 misses the keyhole, there WILL be other threatening asteroids in the future. Doesn’t it make sense to design a mission concept now? Or is each asteroid situation too different to have one concept on the books for multiple contingencies?

  56. Zenzan

    There is a scientist (sorry, I can’t remember who) that has previously proposed using lasers to change the orbits of space objects. The theory is that is you heat a point on the icy outer layers then they push away from the object creating a small amount of thrust away from the burn point.

    Therefore, I would have thought sending one space craft that can meet up with and orbit/follow the object as the object orbits the sun would be all that is needed – it could act on the object as well as report back.

    The space craft would use solar panels to catch sunlight to power the laser and just blast away at one target point, pushing the object out of its normal orbit into a safer orbit. That approach would not only resolve the questions of the effect of an impactor on a space object of unknown composition (solid rock versus cluster of rubble) but would also be a proof of concept to resolve other space object risks in the future.

  57. Number 6

    Fascinating article, Phil!…..Great comments!….I would think it would behoove NASA to put a line item in the budget ASAP regarding this issue, so that if a collision looks likely, they have sufficient funding to get the job done. A deliberate, well-planned budget approach is preferable to a desperate 11th hour plea.

  58. It looks the Sweet Meteor of Death may take a few election cycles:

    http://www.youtube.com/watch?v=qQqQzYUJeVg&feature=related

  59. amphiox

    Llewely @21;

    That would depend on the inclination of the asteroid’s orbit, which I’m not sure is yet known. It’d be hasty to assume it actually makes close encounters with Mars, as it could well be far above or below the ecliptic whenever it is near Mar’s orbit for all we know.

    Though of course we could consider deliberately altering its orbit to make into a nice Earth-Mars ferry! But perhaps for that purpose a slightly larger asteroid would be a more ideal candidate.

  60. amphiox

    Since gravity tractors take many decades to work, I’m wondering if the time window is long enough for gravity tractors alone. Also gravity tractors are a wholly theoretical and untested technology, while kinetic impactors (and nukes) are not.

    I’d imagine that putting an asteroid into earth orbit would be much harder than simply deflecting it from a keyhole or collision. And any error in the attempt would likely increase the impact risk.

  61. Iain Heath

    Perhaps a dumb question, but scanning the article and comments I could not see any statement of what threat is posed by an object of this size. If it were 2 metres across, we would not be having this discussion. If it were 6 miles across, governments would already be freaking out! So, for a 140 metre -ish object, what is the expected outcome of an impact? Surprised this wasn’t actually articulated in the original article. Its implied. But not stated.

  62. Jerry

    I would like to see NASA contract ATK to make 4 shuttle solids as the emergency backup for this project. They are storable and it would maintain the industrial capability until another program matures. They have excess steel cases they do not intend to use for next-gen programs, but are just fine for boosters for any of several programs if they do not need to be used for an asteroid. Not sure a bit of depopulation is not a good thing. Makes it ethically easier when you can declare it an act of god.

  63. Jumpy

    That’s it I’m cashing out my 401k tomorrow.

  64. Timothy from Boulder

    @ Zenzan (58)

    Lasers are not magical death rays with infinite power. They are *horribly* inefficient at changing electrical energy into photons. You would get far more energy impinging on the rock (about 100x) if, rather than solar panels, you used an large reflective panel of the same size and aimed reflected sunlight at the rock. If you want to get a “burn point” (really, it’s an ever-so-slowly-warm-evaporating-point), flex the panel slightly and focus the light.

    The only rationale behind a terrestrial-based laser is the ability to throw millions of joules at the rock … something that would not be possible with a space-based system.

  65. Brian Too

    For anyone thinking of bad outcome scenarios, I expect that there is essentially no impact zone on Earth that is completely safe.

    Any impact upon an ocean would be bad due to the generation of tsunamis. Impacting landlocked ice caps would have unpredictable consequences that might include something similar to a Jökulhlaup. Even most desert areas have some through traffic. About the most you could hope for was a fortunate coincidence that would minimize casualties.

  66. Xander

    @Wzrd1 – I’m not entirely sure that argument works, here, though. For a ‘large rock’, yes, it makes sense that a nuke would – at best – just shatter it. But this one isn’t that big – only 140 meters. While the bulk of a nuclear detonation in the atmosphere causes damage by the shockwave, or other effects of the radiation interacting with the atmosphere…which obviously will not happen in space…there is still a LOT of energy released. After all, a 1.2mt nuke (standard-ish size in US arsenal) creates a fireball nearly exactly a kilometer across. If you set something like that off on or near the surface of a 140m wide asteroid, it would do more than just ‘shatter’ it, but turn it into an ever-expanding spray of molten droplets.

  67. d.graf

    I say it is always better to plain a head and hope the best. I agree with Rusty the observer is need 1) to see if the impact worked with the observer there be almost no lag to for the information as it would be from a earth base. 2) It can be used as a fail safe. I also believe there should be other option set up if they ware to fail. All that takes time if it is not need then at lest we have something set in place for when we do need it.

  68. Chet Twarog

    Why not make an international effort to steer NEOs into a capture orbit and mine it for its organics, metals, etc?

  69. Jim McDivitt

    @Dave Scott (4) – thanks for having Rusty’s back…just like old times ;-)

  70. Michael Wallis

    So … it likely boils down to money. NASA’s budget is very tight and they are struggling. They don’t want another unfunded mandate to sap away money they want to spend on other things, because they don’t think it’s enough of a danger yet.

    So how much are we talking about to do this? A couple of $100K? A couple of $1M? The analysis can’t be THAT expensive – it’s just number crunching with the right data and software.

    Could we fund a Kickstarter to get Rusty the software and data and expertise and computing time to do the analysis based on current data and then update that analysis as more data comes in?

    The other question is how fast can we build a small, simple satellite that can be boosted into a landing or capture by AG5? That’ll be a lot more costly, but it just needs a power source, a radio transmitter, a computer and a landing/orbiting system (yes it’s not that simple, but it’s not a really complicated system). Getting continuous radio data for an orbit or two would be far better than getting a few [dozen/hundred] observations as it swings by Earth.

  71. Messier Tidy Upper

    @42. JL Galache :

    @Messier Tidy Upper #3 – “Any chance of it – and 2012 DA14 – recieving proper names at some point soon~ish?”
    Nope. Before an asteroid can receive a name it must first receive a permanent designation number. In order for an asteroid to receive a number (currently these two objects only have provisional designations) it needs to have been observed during at least 2 oppositions, or as many as are needed for a reliable orbit to be determined. Once a designation number is assigned, the asteroid’s discoverer has 10 years during which to propose a name for it. Once a name is proposed to the IAU’s Committee for Small-Body Nomenclature, it is reviewed and, if approved, is published in the Minor Planet Circulars and made official. If you’re still awake and want more info on asteroid naming conventions (yes, there are rules), click here.
    —Dr JL Galache, Minor Planet Center

    Thanks for your informative comment and the links – very much appreciated. :-)

    @29. Tim :

    @ #3 – “How does that compare with the size of cricket oval, BA?”
    Lords (ENG) Cricket Ground is ~230 meters, making it impervious to meteor strikes. Wembley (ENG), an actual Football stadium, is easily double that of your average American Football stadium and while it is also impervious to meteor strike it is highly susceptible to a miserable performance and uninterested crowds.

    Cheers for that. :-)

    @ 21. llewelly :

    What I cannot believe is how blind both NASA and Schweikart are. They are missing out on a golden opportunity! Any idiot can see that not only does this asteroid sometimes pass close to Earth, it also occasionally passes close to Mars! After all the decades people have spent trying to find a way to get to Mars, it is amazing that such smart people should entirely fail to see the implications of an asteroid, which will take us elliptically to Mars, falling into our laps! Rather than agonizing over whether or not it will hit us (unlikely), we should planning to colonize it as soon as it arrives. Then, when the asteroid makes its next close approach to Mars, we can colonize Mars! Percival Lowell, honored astronomer of the great clear-skied state of Arizona, would spin in his grave if we shirked this opportunity.

    Good suggestion but 2011 AG5 certainly isn’t the only asteroid that does this. We know of whole classes of Earth-Mars and even Mercury crossing asteroids with orbits that intersect two or more planets.

    Patrick Moore, if memory serves, suggested a science station be planted on Icarus an asteroid that swings in closer to the Sun than Mercury at perihelion, close enough to glow red-hot and whose orbit is so far out at apohelion that it crosses Mars.

    Mind you, just because it crosses a planet’s orbit doesn’t mean its near the planet at the time. Planets are awfully small moving targets amidts the vastness of space and chances are that encounters with planets even relatively near (or even medium?) misses are extremely rare with the planet being very distant most of the time their paths cross. So we’d need to choose our rock carefully if we’re to get one that intersects regularly or conveniently for that idea to work.

  72. Messier Tidy Upper

    We know of whole classes of Earth-Mars and even Mercury crossing asteroids with orbits that intersect two or more planets.

    See :

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

    Note the first known namesake example of an Apollo asteroid the eponymous 1862 Apollo has an orbit that crosses the orbits of Mars, Earth and Venus.

    Plus see :

    http://en.wikipedia.org/wiki/1566_Icarus

    for Icarus info – although no mention there of the idea of planting a science station on it.

    There’s also this :

    http://www.youtube.com/watch?v=km38S3zHzWM

    good Youtube clip on Icarus with animations of its orbit and more.

  73. Moodie-1

    There’s another danger here. As with any asteroid, even if 2011 AG5 misses us in 2040 a close-enough approach would probably cause it to assume a much tighter orbit relative to the Earth (due to the Earth’s gravity). This would greatly decrease its orbital period and increase the chance of it hitting us on some future pass. Which is even more reason to alter its course now, while it’s still possible.

  74. So besides doing the ‘make it miss’ math and planning —

    I’d really like to see the “catch and release” workup,
    along with the “add a transponder and remote controlled ion engine” workup.

    Phil, here’s your big chance for a Kickstarter.

    If we chip in on the cost of eventually capturing the thing, do we own it?

    Or is that ruled out by treaty?

  75. Sure NotSure

    I would vote for making the study while we can without waiting. The cost would be minimal compared to the cost of cleaning up the potential mess afterward.

    Gosh, if we just pooled the spare change under our couches and took up a collection, we could at least start the process.

    If worse came to worse, we could put out bids for naming rights — if you can name a sports stadium for huge sums of money, we can certainly allow for the chance to name a NEO for even bigger bucks and let some corporation pay for the rights not to kill us all. (In name only, of course.)

    “This salvation of humanity brought to you by XYZ, Corp….”

    I could live with that.

  76. Patrick Moore, if memory serves, suggested a science station be planted on Icarus an asteroid that swings in closer to the Sun than Mercury at perihelion, close enough to glow red-hot and whose orbit is so far out at apohelion that it crosses Mars.

    Turns out Arthur C. Clarke suggested that not Patrick Moore but I read about it in a Patrick Moore book :

    ” Sweeping in from beyond the orbit of Mars, the tiny asteroid Icarus passes only 17,000,000 miles from the Sun, closer even than Mercury. As it does so, its surface is so intensely heated that it must glow red hot. Arthur C.Clarke once suggested tat inits cool cone of shadow or well dug in beneath its surface, scientists might use Icarus to put themselves and their equipment close to the Sun shielded by its 10,000 million ton bulk.”

    Source : Page 24 , The New Challenge of the Stars, Patrick Moore & David Hardy, Hutchinson, 1977.

    I think at the time Icarus was the only known Mercury crosser asteroid although I’m pretty sure we know of a number of others today. The same idea would surely apply to other Mercury crossers too – although I suspect Icarus is the largest and thus probably best candidate.

    PS. Artists impression – David A. Hardy’s – of Icarus at perihelion linked to my name here.

  77. HarryR

    How heavy would an impactor need to be to make a worthwhile effect on an asteroid? And how fast relative to the asteroid would it need to be going when they hit? Put another way, what is the total energy required re mass * velocity?

    Rather than lifting an appropriate mass from Earth and accelerating it, would it be possible to deflect a smaller asteroid to act as an impactor? Then we just need to lift the fuel into orbit and not the fuel plus the impactor mass.

    Given the global nature of the risk then we should make it a global response, like CERN. As was observed in previous comments this sounds like a useful exercise and would bring awareness of the reality of asteroid strikes to a wider public. Humanity united in a common purpose to protect the Earth! My heart flutters and my eyes moisten.

    If we were to leave it for future decades by which time we assume tech will have evolved to make it easier, what if some crisis such as economic collapse, pandemic, political crisis, natural disaster distracts the world from doing it? And the later the eventual solution is applied the more difficult it will be, negating the purported benefit of assumed, new technology.

    The nuclear option. Do we really want to turn one big rock on a predictable (eventually), stable orbit into a vast, expanding cloud of radioactive space junk? An impactor might have the same, non-radioactive, result. And may not succeed in deflecting all the parts of the whole asteroid.

    The gravity tug applied early seems a tidier method.

    Another task to be considered is to plan for some monitoring system to locate all possible Earth impactors that are out there. They don’t need to be very big to have a drastic human cost if they hit the Earth.

    What would a comprehensive system need to be comprised of that could detect impactors from any direction as early as possible? A network of multiple space telescopes in deep space orbiting the Sun at about the distance of Jupiter in various planes? Can impactors only be detected visually?

    What other useful purpose would such a system achieve to leverage the costs? Would it be useful to survey what’s out there for future mining? Or to gather useful science info?

  78. Josh

    Read a while back about somebody’s theory to grab something like this and park it in orbit to mine it. Sounds like a munge of a bunch of sifi crap right now, but hey, there could be diamonds or other previous metals there, right?

  79. Murgatroyd

    OK, we know that *IF* 2011 AG5 hits us, it will impact on February 5, 2040. The time of impact can be nailed down to within a few minutes, otherwise the rock will miss us — Earth’s orbital velocity is about 30 kilometers per second, so our planet moves a distance of its own diameter in about seven minutes. We also know the exact trajectory of the rock as it approaches us, of course.

    So … One hemisphere of the planet will be facing 2011 AG5 as it’s coming in for the kill, and the other side of the Earth will be completely safe (except for seacoasts, if the rock splashes into an ocean). Who is at risk, and who isn’t? If Europe or China are in the crosshairs, shouldn’t they be making contingency plans? How big a splash would AG5 make if it came down in the Pacific?

  80. Geek

    @Dave #13

    Great point! If the odds truly represent the best of our current knowledge, it only adds confusion to talk about how they’ll “probably change”.
    It reminds me of a line from “The Naked Gun”:
    “Doctors say that Nordberg has a 50/50 chance of living, though there’s only a 10 percent chance of that. “

  81. Andreas H

    While there is little to argue against “earlier is better” in a general sense, I fail to see a compelling argument of “waiting 1.5 years will cause any possible mission to fail”. I don’t even see an argument that waiting 1.5 years will cause a potential mission to exponentially be more expensive. If we wait until September 2013 we will know whether or not AG5 is a threat, so spending resources on a hypothetical mission analyses seems a little premature.

    We should not forget the fact that with better observation technology we will see a lot more potentially threatening objects surrounding us. If we start to cry “wolf” every time and demand to allocate precious resources immediately we might at some point no longer get those resources when we would really need them.

  82. pie in the sky guy

    Kind of a sci-fi idea, but why not kill a few birds with one stone?

    Launch a maneuverable satellite that can be used to target and “consume” dead satellites and space junk. As it gathers up more debris, it’s increased mass makes it a useful potential kinetic impactor. When needed, it can maneuver itself into a trajectory that would impact worrisome asteroids.

    Then again, I’m no rocket scientist.

  83. @47 Miguel “So if we push it out of the way now, what happens to future orbits? Did we change the odds off it hitting us on future passes?!”

    If it hits us in 2040, it will not hit us later on. So yeah.

  84. Nigel Depledge

    Jeremy Greenwood (23) said:

    Why not just nuke it? I know the arguments about converting 1 big impact into a lot of moderate impacts, which may well be worse; and that a loosely constructed body might absorb most of the force and not move very far.
    But, I would value some amplification on these objections.
    Surely, in theory, if the object was smashed into pea sized pieces we would suffer no more than a glorious meteor display (albeit radioactive). I doubt such fine fragmentation would happen in practice, but would not smaller pieces (hopefully not many of a dangerous size) be easier to move out of the way?
    With regard to the second objection, a football stadium is surely rather small in the face of a nuke, so could we not expect a significant change of orbit, especially if performed early?

    On Earth, nukes have two processes through which they exert their destructive power – radiation (thermal and otherwise) and shock wave.

    While the radiation is devastating to living things, what mostly causes the destruction of buildings and so on is the shock wave. This shock wave propagates through air and, to a lesser extent, through the ground (very much lesser if the device detonates above ground level).

    In space, there is no air, so there will be no shock wave. If you detonate a nuke near an asteroid, all you would be doing (from the asteroid’s point of view) is shining a bloody great light at it (OK, lots of X-radiation in that light, but still just a bloody great big light), and throwing a handful of fission by-products at it. The asteroid won’t shatter into a thousand pieces, and its course will change by a trvial amount (radiation pressure being not very much, especially when exerted only for a few seconds).

    You would probably have a larger effect on the asteroid’s course if you park a big lump of uranium near it for a couple ofyears. And this would simply be another form of gravity tractor.

    Besides, sending nuclear weapons into space violates the Outer Space treaty.

  85. #34 Kappy:
    The earlier we act, the smaller will be the change of velocity required. A tiny nudge leads to a far bigger change in its position years in the future.

    #44 Greg:
    Capturing the asteroid into Earth orbit would require a velocity change several orders of magnitude greater than that required to nudge it into a safe orbit. It could certainly not be done by the same technology.

  86. Nigel Depledge

    Kappy (34) said:

    Maybe I’m missing something here, but if it turns out that the asteroid WILL in fact pass through the keyhole, why would we have to do something now? If we find that it does indeed pass through the keyhole in 2023, we would still have from 18 months from now (mid-late 2013) until sometime near 2040 to do something. Isn’t it likely that we will have much better tech by then to move the asteroid at lower cost or more efficiently / safer? I realize if we go the gravitational tractor route it may take a while to alter the course, but will it really take longer than a decade? Two decades?

    For this kind of thing, the sooner we do something about it (assuming we think it will pass through the keyhole in 2023), the less we will need to do. The later we leave it, the bigger and more complicated the mission needs to be to achieve an adequate deflection.

    Since it takes us time to get even as far as designing hardware, I guess it is a case of “the sooner, the better”.

  87. Nigel Depledge

    Ach!

    My shadowy nemesis strikes again. Curse you, Neil Haggath, for beating me to answering post #34!

    ;-)

  88. Nigel Depledge

    Calli Arcale (37) said:

    2011 AG5 might not get us, but somewhere out there, there is probably an asteroid with our name on it. It would be good to be prepared.

    Surely the safest bet, then, would be to avoid ever naming an asteroid after Earth?

    ;-)

  89. @82. BerndB : “If it hits us in 2040, it will not hit us later on. So yeah.”

    Well, maybe – but then 2011 AG5 just possibly, hypothetically, *could* bounce off back into space if it hits hard enough and then fly round to impact us again later couldn’t it? If it’s, say, composed of rubber and structured like a ping-pong ball! ;-)

    @52. roymeo : ” Push it into Mars!”

    What, and start an interplanetary asteroid fight with the Martians!? :-o

    @ 79. Josh : “.. but hey, there could be diamonds or other previous metals there, right?”

    One word for you – Voga! ;-)

    (Link in my name.)

  90. jeremy greenwood

    Thank you everyone for your helpful replies to what I feared might be a dumb question

  91. Nigel Depledge

    Xander (68) said:

    After all, a 1.2mt nuke (standard-ish size in US arsenal) creates a fireball nearly exactly a kilometer across. If you set something like that off on or near the surface of a 140m wide asteroid, it would do more than just ‘shatter’ it, but turn it into an ever-expanding spray of molten droplets.

    And what is that 1-km fireball made of? Ionised air. Mostly.

    The only mechanism a space-borne nuke has to transfer energy to the rock is radiation – so you’d surely melt the surface on one side, but to what depth, and with what change to the asteroid’s trajectory?

    If you were able somehow to land on the rock and bury the nuke, then you might get somewhere, because when the nuke detonates, it’ll have some rock around it through which to transmit a shock wave. It’ll probably make a small crater on the surface and will eject some material into space. If this stuff is ejected fast enough, it’ll (briefly) act like a rocket, causing a thrust in the opposite direction (IIUC, the ejected material must exceed the escape velocity of the rock because otherwise the ejecta will pull back on the rock at the top of its trajectory and the net thrust ends up being zero). But the amplitude and direction of this thrust would be very hard to predict.

    A gravity tractor is probably the best bet, because we can predict exactly what it will do.

  92. beer case

    #90 Nigel Depledge: What if we can manage to set off the nuke exactly when it hits? We could use some kind of triggerswitch in the (elongated) tip of the missile? The asteroid must be mostly solid, though.

  93. beer case

    Wrong number! I ment post #94, of course! :)

  94. OneofNone

    @54. Wzrd1 and others:

    As was mentioned by one above, if it’s a rubble ball, an impactor just gets absorbed with minimal change in velocity.

    That is not true. There is no real difference if the target is very stiff or very soft. We are just talking impulse here, vectorial values. If the impactor is fully absorbed, the change in impulse is exactly the same. With a rubble pile the impactor gets deeper, which takes more time. Unless of course the impactor is not absorbed, but shoots right through. Not likely.

    The only difference on a stiff target: You get the energy near the surface. This may blow out some matter, acting like a rocket drive. But I doubt this has that much effect.

  95. OneofNone

    @68. Xander

    After all, a 1.2mt nuke (standard-ish size in US arsenal) creates a fireball nearly exactly a kilometer across. If you set something like that off on or near the surface of a 140m wide asteroid, it would do more than just ‘shatter’ it, but turn it into an ever-expanding spray of molten droplets.

    It will not just turn into droplets just for the energy. Even if you melt the total stone, at that point it is just a big drop. To turn that into droplets you need to heavily push it, i.e. you need a shockwave. Which you do not have.

    And to melt it: We talk about roughly 3.5 million cubic meters of stone. To melt that requires a huge amount of energy, efficiently transferred to the mass. The short flash of the nuclear explosion is not necessarily an effective way to do the job 100m deep.

  96. OneofNone

    @70. Chet Twarog:

    Why not make an international effort to steer NEOs into a capture orbit and mine it for its organics, metals, etc?

    We simply do not have the technical options to do so.
    As was said, diverting the asteroid requires a delta-V in the order of some cm/s. Putting the stone into orbit requires delta-V of some km/s. This is a factor of ten thousand.

  97. Jim

    “The orbit of AG5 brings it close to Earth every few orbits.”

    And presumably has been doing so for many years. Why, then, didn’t we detect it before 2011?

  98. Nigel Depledge

    Beer case (95) said:

    #[94] Nigel Depledge: What if we can manage to set off the nuke exactly when it hits? We could use some kind of triggerswitch in the (elongated) tip of the missile? The asteroid must be mostly solid, though.

    IIUC, the device needs to have some stuff that it can throw in the opposite direction to generate thrust. So whether it is detonated at the surface or 100 m away f4rom the surface, you’re still only heating the surface of the rock. If it detonates at the surface, you might also crack the rock, but this by itself won’t generate much impulse.

  99. Nigel Depledge

    One of None (97) said:

    That is not true. There is no real difference if the target is very stiff or very soft. We are just talking impulse here, vectorial values. If the impactor is fully absorbed, the change in impulse is exactly the same. With a rubble pile the impactor gets deeper, which takes more time. Unless of course the impactor is not absorbed, but shoots right through. Not likely.

    I disagree. A rubble pile could behave like an enormous Newton’s cradle, i.e. you might get some small percentage of it exiting at very high velocity opposite where the impactor strikes, but the bulk of it mostly not changing direction (except maybe spreading out into a cloud for a while before re-aggregating).

  100. Nigel Depledge

    Jim (100) said:

    Why, then, didn’t we detect it before 2011?

    It’s small and dull and nobody was looking for stuff like this until recently.

  101. Murgatroyd

    I’d hoped my question would be answered by now. It should be simple enough to determine, if you have 2011 AG5’s orbital elements and NASA’s mission planning software:

    On February 5, 2040 at the time of possible impact, which half of the Earth is facing AG5 on its way in, and which half is facing away and can’t possibly be hit?

    Anyone? … Anyone? … Bueller? … Anyone?

  102. Timothy from Boulder

    It’s slightly more complicated than which hemisphere is pointed away at time = X, since different trajectories which would impact at different places occur at different times. Also, Earth’s gravity would have an increasingly important effect in the last 15-20 minutes before an impact, so you could have a grazing over-the-horizon impact. So the potential impact zone is greater than a hemisphere. However, it does look like if you’re in Australia or India, you’re safe.

    See a risk corridor analysis at:
    http://astrogatorsguild.com/wp-content/uploads/2012/03/RiskCorr2011-AG5r2.pdf

  103. Timothy from Boulder

    An addendum (which won’t make complete sense until my previous post with a URL is moderated) … the trajectory as of the known observation can be extrapolated to a fairly narrow line that spans a portion of the globe.

    According to the analysis derived from the most recent observation, South America (Bolivia, Brazil, Peru), and the very southern tip of Africa are the only land masses affected.

  104. Murgatroyd

    Thank you!

    However … I think that one of us has mis-read the paper.

    As I read it, the endpoints of the line on the map represent the extreme cases in time uncertainty — the closest miss points on the Earth’s leading and trailing edges — and the line on the map indicates impact possible impact points for test-particle trajectories that come closest to the center of the Earth’s cross-section at the times of impact. *IF* the uncertainty in latitude (or in ecliptic latitude β, which should be similar) of the trajectory is more than a few thousand kilometers, then the “impact footprint” on the Earth’s surface would be a circle somewhat larger than 10,000 km (i.e., a quarter of an Earth circumference) centered on a point off the coast of Peru and about 10 degrees south of the equator. This would put North America, South America, Hawaii, and some of Europe and Africa at risk.

    So the potential impact zone is greater than a hemisphere.

    Yes …

    … the trajectory as of the known observation can be extrapolated to a fairly narrow line that spans a portion of the globe.

    Here’s our disagreement — what does that narrow line represent? If there’s any uncertainty in latitude, that narrow line spreads out into a wide band, possibly a band wider than the Earth’s cross-section. You’re apparently saying that there’s no uncertainty in latitude, which seems highly unlikely to me.

  105. curt newsom

    Is it possible that the actual worst case scenario is a head one impact with the moon? Its orbit would be a potential 450000 plus mile target with a smaller bullseye and perhaps four opportunities to intersect. With no atmosphere to lessen impact, would it break big chunks off or degrade the orbit until an earth moon collision. The earthquake in Japan last year slowed the Earth in its orbit and this would possibly be a relatively larger impact to the moons orbit.

  106. Kevin in Sacramento

    @109 (Curt),
    The Japan Earthquake in March 2011 did NOT change the Earth’s orbit. AG5 is too small to perturb the orbit of the moon, much less cause an Earth-moon impact. The moon has been hit by many larger objects without crashing into the Earth.

  107. Robert in Canada

    The way we are going, there may not be much of an organised society left to be impacted by this big rock anyway…..Let’s just roll the dice and see what happens…..that is, after all, our usual preferred behaviour….regards to all…

  108. JD Eveland

    It would certainly be a lot more fun spending money on this project rather than, say, on invading a small country. If we succeed, there will probably be fewer casualties than the war would entail (although not necessarily if we fail), while still allowing as much whooping it up with incredibly fancy electronic toys. And we should have little difficulty justifying this expense, since certainly the asteroid could be established to possess Weapons of Mass Destruction (i.e., itself). All that’s necessary now is to determine if the asteroid is in regular communication with Al Qaeda operatives…

  109. I think that the asteroid capture scenario should be seriously considered. With new asteroid mining ventures in the news recently, AG5 seems like a prime candidate. Another post stated that the amount of energy required would be huge, but it seems to me that in fact the orbit would only need to be shifted into that very slim window between impact and non-impact in order to bring about capture (maybe i am wrong, obviously it would be quite a close earth graze until the orbit settled down).

    Maybe too risky to stomach, but capturing a few billion tons of asteroid ore into earth orbit would be a mighty tempting venture to some. I suppose a safer option would be to just jump onboard in 2023 and start mining, with a view to dropping off some ore on each revisit through the 2040s.

    Just for the record, this was all my idea, and I will collect royalties from all AG5 asteroid mining ventures inspired by this post ;)

  110. Kevin in Sacramento

    inchiki,

    Currently we are not capable of capturing an asteroid larger than about 7 meters in diameter. AG5 is simply too large to capture with current abilities. It takes a lot more energy to lift a guy off a bike with my bare hands than it does to simply knock the bike down.

  111. Anonymole

    A few points, months later, but still apropos:

    • There will be multiple opportunities to influence the orbit of AG5. If it orbits ever 1.7 years in 20 years we’ll have 15 or so “passes” at altering its orbit. Yes each later pass will require greater impetus, but imagine the tech we’ll have in 10 or 20 years.

    • This is just one asteroid. There are hundreds of thousands of them in our plane and in our vicinity. A 30 meter asteroid hits Earth, on average, once per year. The odds that we will discover a AG5 every year for the next 100 is considerable. We WILL be impacted by a catastrophic asteroid/comet in the next 100 years. We need to plan NOW. We might detect a 400k ton country killer next week – what then?

    • If we ever do have to nudge an asteroid out of the “keyhole”, and succeed, we will end up creating a new keyhole event years down the road. We need to plan to nudge again.

    • The design of the interceptor vehicle should be of a single design – both observer and impactor. Each unit must be able to perform double duty. Simplifies design and lowers cost. Not only that, we need to be able to send up a swarm of them so that we don’t “miss”; we need to have contingency failure planned into the mission.

    • Lastly, we need a new launch technology. Rockets are so 14th century. “Light the fuse and run like hell” just doesn’t work as a LEO launch technology. What NASA needs to focus on is a new 21st century launch technology. Some Startram, maglev, scramjet, railgun like tech to get lots of mass, up into LEO so that we can deploy a swarm of Asteroid Attack Auto-impact bots.

    NASA needs to hold a contest to see what team can design the best AAA bot and then we need to build and launch them.

  112. Aubiting

    read NASA Report 460 feet (140 meters) no football stadium size
    http://neo.jpl.nasa.gov/news/news175.html

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