Apophis danger downgraded

By Phil Plait | October 7, 2009 1:00 pm

apophis_orbitApophis is a 250-meter-wide rock with a special designation: it’s a near-Earth asteroid, meaning it passes close to our planet. In fact, in April of 2029 it will pass so close to the Earth — just under 30,000 kilometers (18,000 miles) — that it will actually get between us and some of our geosynchronous satellites!

Because it will come so close, the Earth’s gravity will change its orbit. There is a region of space called a keyhole (it’s actually kidney-bean shaped) and if Apophis passes through it like an arrow through a bulls-eye, the Earth’s gravity will change the asteroid’s orbit enough that in seven more years, in 2036, Apophis will hit the Earth! The odds of it passing through the keyhole are low; up until recently they’ve been quoted as 1 in 45,000. Not a huge concern, but worth keeping an eye on.

However, new observations have lowered these odds even more, to only 1 in 250,000. Pretty much at this point I’m not worried about this particular rock any more. The odds before weren’t great, but they’re so bad now it’s no big deal.

How does this work? The orbit of an asteroid is calculated using measurements of its position in the sky over time. There is a tiny uncertainty in those positions for many reasons: atmospheric distortion blurring the asteroid image being one of if not the biggest. The way to minimize that is to get lots of images so that the errors average out, but even then the orbit calculated has uncertainties. And the longer into the future you project the orbit, the worse it gets. In the case of Apophis, astronomer Dave Tholen used hundreds of new images of Apophis to refine the orbit and get the better statistics for its impact risk.

This happens quite frequently: a potentially dangerous asteroid gets better observations made of it, and the risk drops. In this case, that’s definitely a good thing. At 250 meters wide, an Apophis impact could do considerable damage to civilization. It wouldn’t be an extinction level event, but it would put serious hurt on humans. Still, it bears watching. I doubt the odds will go back up, but the more we pay attention to these things, the better!

Image credit: UH/IA.

CATEGORIZED UNDER: Astronomy, DeathfromtheSkies!

Comments (72)

  1. Levi in NY

    I’m actually rooting for something to hit the Earth. Not something big enough to cause serious damage, but something big enough to create a nice boom. In an uninhabited stretch of land somewhere, of course. And we should be able to see it coming so we can set up cameras to catch the explosion.

    What kinds of offerings to the Flying Spaghetti Monster would work best to achieve this result?

  2. Steve VanDevender

    It might have been better to say Apophis will “get closer than our geosynchronous satellites” than “get between us and some of our geosynchronous satellites”. The chance it would actually pass in front of a geosynchronous satellite as seen from somewhere on the Earth’s surface is really, really tiny. Also, if it passes at that projected distance, it would be closer to us than any geosynchronous satellite, not just some of them, since they’re all very nearly the same distance away.

  3. Mooney

    Great. Good. The chances of Earth’s mass curving the orbit of Apophis so that it would wind up impact is vanishingly small. That’s awesome.

    Now, if only there were some way for us, being the semi-aquatic plains-dwelling monkeys that we are, to purposefully alter Apophis’ orbit so that it eventually inserted into a stable, reachable, orbit around the Earth.

    I mean, it’s not like we get rocks this size coming this close with such possibly profitable orbital mechanics every other day, right?

    Ah, but what am I dreaming about? We’re ground-bound monkeys, and it’s far more important for us to spend money figuring out which talk-show host yells the loudest.

    (I don’t know why I’m bitter about this sort of thing today. But thanks for the opportunity to vent)

  4. Can we still shoot Ben Affleck into space?

  5. L O'Neill

    I know of the (really bad) movie to which you refer, but I can think of a lot more people I would like to shoot into space besides Ben Affleck!

  6. Too bad they didn’t publish this before TAM London … you could have had updated your speech 😀

  7. tacitus

    Now all we need is a ginormous net and we can snare this thing as it hurtles by… :-)

    …or at least be ready with a harpoon and hitch a ride on the sucker!

  8. Calin

    I don’t know, that one and Pearl Harbor? He’s mighty deserving.

  9. @L O’Neill: Okay, Ben can lead the “B” Ark, then.

  10. Gadfly

    Curious…when this thing passes by will it be naked-eye visible? Opinions?

  11. NewEnglandBob

    And I thought Apophis was only a meanie character in the TV show Stargate SG1

  12. Brandon

    Not that it matters, since the Mayan calendar ends in 2012 anyway… 😛

  13. TigerHunter

    Only 1/250,000? Good. If it was 1/1,000,000 we all know it was a sure bet.

    And @11, the asteroid was named after him if I recall correctly.

  14. What? 2036 is only seven years away? I should be retired by now! So why am I still working then? Think I’ll take the rest of the day off at least. Thanks for letting me know.

  15. Does anyone know if an object that size passing that close will have a noticeable or measurable effect on, say, tides?

  16. TGAP Dad

    Hey, since Apophis is giving us such a close approach, can we try the gravity tractor, just as a proof of concept? It seems a shame to to have it come right up to the stoop without even offering so much as a “hello.”

  17. @Levi in NY, as callous as it sounds, me too! Just to have politicians actually get serious about funding sky mapping technology and the technology to actually DO something about the possibility of Chapter 1 in Death from the Skies. We all know that politicians, and people in general, don’t actually think about things or worry about things until AFTER they happen…

    @artbot, no effect what so ever that anyone would notice. Its mass in relation to the earth/moon system is just too low.

    @NewEnglandBob and TigerHunter, actually that Apophis is actually named after an old Egyptian diety: http://www.touregypt.net/featurestories/apep.htm

  18. Mount

    I’m all for getting a new moon! Maybe we could even give our Moon it’s own moon, that would really mess up some horoscopes!

    “Shova ‘cree!”

  19. Flashback: Hale-Bopp Heaven’s Gate UFO [http://en.wikipedia.org/wiki/Comet_Hale-Bopp#UFO_claims]


    @ Gadfly,

    According to this article, "Closest Flyby of Large Asteroid to be Naked-Eye Visible", in Space.com, 99942 Apophis (2004 MN4) will become as bright as magnitude 3.3 (visible to the naked eye from rural as well as darker suburban areas and visible with binoculars from most locations).

  21. JoeSmithCA

    I wonder if homeopathy will work on the asteroid :)

    @Mount (#18)
    I think we should have it slam right into the moon. Talk about a way to test for water 😉

  22. havoc

    An un-careful reader could read:

    “This happens quite frequently: a potentially dangerous asteroid gets better observations made of it, and the risk drops.”

    and understand it as. “We lower the risk BY better observing the dangerous asteroid.”

    Language is funny!

  23. Mount

    @ Joe Smith

    We’re trying to find water, not obliterate it!

    And for SG1 fans, I just found this on Wikipedia: “The astronomers David J. Tholen and Roy A. Tucker enjoyed the SG-1 arch villain Apophis so much that they named their discovered near-Earth asteroid “99942 Apophis.”

  24. XMark

    I’m kind of hoping that a huge asteroid is found heading towards the Earth. We have the technology to deflect them, and if one was found on its way to us we’d have no choice but to launch a rocket up with explosives large enough to knock it off course. The end result being a triumphant victory and all sorts of funding and attention to the space program. It would be just the kick in the butt we need to get space exploration back on track.

  25. Robert E


    Depending on it’s composition, the last thing we’d want to do would be to blow it up. You’d go from trying to dodge a bullet to trying to avoid scatter-shot.

  26. Steve

    Since we’re all supposed to die in 2012 (Thanks, Mayan Calendar Myth!), what difference does it make?

  27. Theron

    Ah well. Worldwide destruction from Apophis was kind of my “retirement” plan. I guess it’s back to the salt mines.

  28. Hmm – and you were talking about just this at TAM London. Maybe all our clapping helped to push our planet off course.

    Or not.

  29. holastefan

    Wait, you mean I painted all these “The End is Near” signs for nothing?! Now nobody is going to repent, and I’ll have to rant about something different.

  30. Chris A.

    @5 and 8:
    Not to mention “Gigli.” Sorry, I just threw up in my mouth a little.

  31. Monkey

    Will it pass by any other notable planets – well, I suppose they are all noteable! – along its journey here? The Jupiter, the Neptune or the Saturn? The Earth getting the only show?!?

    PS – Earth….not THE Earth. Please!

  32. John

    This sounds like an excellent opportunity! Are there any organizations that plan on trying to interact with the asteroid (capture it, tether to it, blow it up, whatever)? Heck, even pasting a transmitter to it so it pings every sec might be neat. :)

  33. Cleon

    Stand down, SG1.

  34. Will Apophis pass directly between Earth and Moon? How frequently does it orbit Sun?

  35. @ 29, perhaps you could just edit your signs to read “The end is Nearly Near”? which is a little more catchy than “The end is passing by but with luck may experience orbital perturbations that will send it crashing into us next time around”

  36. JoeSmithCA


    I think we should send a robot to paint the words “This is the end!” on the front of Apophis. On the backside we could paint “Sorry, maybe next time.”

  37. GaterNate

    Since it’s named after the sg1 villian Apophis I’m betting we can expect it to surprisingly show up at least 5 more times after we think it’s really gone.

    So, does this mean that in one out of every 250,000 parellel universes, Earth is getting wiped out? Seriously, I’d like to know that.

  38. Owen

    I’m with #16 on this one. We’re not going to get too many chances like this to give the gravity tractor idea a test run. Ah, but you know, testing something that could save us all from certain doom? That costs money. Best just to try it on the fly, right?

  39. JoeSmithCA

    Well, you know we could easily fund missions by gambling in Las Vegas on exactly how far Apophis misses the Earth. People are more interested in gambling for money at really long odds then potentially saving their life at long odds.

  40. Can’t we just whisper in someone’s ear that a gravity tractor might also have military applications? Then it should get all the funding it needs to be ready in time.

  41. John Baxter

    I’ve been thinking that Apophis was moot for me. I keep forgetting how far along the arrow of time we are. If I were still around, I would be 90 for the 1929 pass and 97 for the potentially unfortunate one. Unlikely, but not impossible.

    Enjoy the shows, kids.


  42. Hey, why don’t we stick an ion engine on it (hellooooo, VASIMR) and drop the thing into low-earth orbit? Let it hit the earth, but as packets of ore! It could be worth billions.

  43. Travis

    Perhaps we should test out technologies for asteroid diversion out on it. It will be coming close enough for an experiment but isn’t a dire life-or-death situation where we HAVE to get it right the first time. Some practice at such techniques could prove valuable when a real potential impacter is spotted.

  44. Tim G

    GaterNate (#36),

    I’d bet that if we duplicate this Universe in it’s present state ten million times Apophis would miss the Earth all ten million times. We should be able to measure the asteroid’s position and velocity much more accurately.

  45. Tim G

    In light of all the media fuss over Apophis, this is what I want to know:

    What are the odds of a more destructive impact (by another asteroid) before 2036?

  46. Plutonium being from Pluto

    Good news – and I still reckon the close pass gives us a great opportunity to try for a Near Earth asteroid study spaceprobe mission. Perhaps even a manned landing on Apophis could be possible maybe? :-)

    Would be awesome if the shuttle could land on it or something like that! 8)

    NB. Apologies if this idea has been raised already – I haven’t read the comments yet – running out of time at the library & can’t post from home for some reason. – PBFP (aka StevoR) :-(

  47. Plutonium being from Pluto

    @ 31. Monkey Says:

    PS – Earth….not THE Earth. Please!

    Huh? Same planet, same difference – what’s the problem for you there?

    @ 33. Naked Bunny with a Whip Says:

    … How frequently does it [Apophis] orbit our Sun?

    Quite a lot more frequently than it orbits any *other* star I’d think! 😉

  48. Nigel Depledge

    Plutonium being from Pluto (45) said:

    Would be awesome if the shuttle could land on it or something like that

    What would be even more awesome is if the shuttle had been capable of reaching an orbital altitude of 30,000 km in the first place. IIUC, the orbit of Hubble (about 600 km up) is the furthest from Earth the shuttle can reach. It simply doesn’t carry enough fuel to get higher.

  49. Nigel Depledge

    @ everyone speculating about using a gravity tractor on Apophis –

    How else do you think Earth is altering Apophis’s orbit? We already know that a gravity tractor will work, because we know how to predict the effects of gravity. What benefit do we obtain from some random test on a rock that is mostly harmless?

  50. Nigel Depledge

    Phil, were you aware that the USAF recently carried out an exercise to test the readiness of various emergency management systems to see how we would cope with a 50 m impactor?

    New Scientist ran an article on this a week or two ago, and I kept thinking: it’s rather like chapter 1 of DftS! And they didn’t even mention you once!!

  51. @Plutonium being from Pluto: You added a word to my question, which was actually a tongue-in-cheek response to #31.

  52. Jason

    I move that we assemble a team of heroes to intercept Apophis. Instead of hairdressers and telephone booth sanitizers, I propose the following persons:

    – Nancy Grace
    – Lindsay Lohan
    – Bill O’Reilly AND!! Keith Olberman
    – George Bush (the younger) AND Hillary Clinton
    – The Fox executives who cancelled Firefly.

    Of course, with current technology, this would be a one-way trip, but these folks would be making the ultimate sacrifice for humanity.

    (Remember: noone tells them that it isn’t really going to hit the Earth. They are our last, best hope for *snort* human… *laugh* humanity *snicker*)

    (Also: thanks and RIP to Douglas Adams).

  53. mike burkhart

    I have a question if Apophis is going to hit the Earth what do we do about it .nuke it? the fact is this is not an option because you would turn one big rock into thousands of big chunks all headed for Earth thus we make the problem worse

  54. Gary Ansorge

    24. XMArk:

    Nah! What we REALLY need are aliens threatening OUR WAY OF LIFE,,,then we could get all the big bucks and investment we need to develop the High Frontier.

    44. Tim G:

    If you mean DETECTED asteroids/comets, the odds are nearly zero however,,,for anything currently UNDETECTED,,,let’s just say OH MY GOD WE’RE ALL GONNA DIE,,,or maybe not. If they’re UNDETECTED we just don’t know.

    Now, doesn’t that make you feel better?

    We know about 90% of the bodies in an equatorial orbit around the sun and they’re all pretty safe (as far as WE’RE concerned). For random rocks coming in from North or South of the ecliptic we have little observational data so OH MY GOD WE’RE,,,hey, the universe is a chaotic, violent, beautiful place. How does that Randy Newman song go, “This world(read universe) we all love so much just might be trying to kill you,,,”.

    Every night I like to go outside, moon the sky and yell, “Hah! Missed again, Turkey!”.


    GAry 7

  55. Eighthman

    Yeah, great, except now there’s a possibility of impact in 2068.

  56. Alan B.

    For more information about Apophis and all other near-earth objects check out http://neo.jpl.nasa.gov/.

  57. Gary Ansorge

    One of my favorite SciFi scenarios is a fairly large(say 10 Km) solid nickel/iron asteroid with exactly the right(read: low) velocity that enters the earths atmosphere at an angle, dipping to around 50 miles above the surface, shedding JUST enough velocity to assume a highly elliptical orbit around earth and having a gradually decaying orbit(say, impact with the surface in 50 years or so). THAT would certainly impel us to DO SOMETHING. I’d like to point out that such a scenario would also produce super heated air in front of the object as it dips into the atmosphere on every orbit,(compression effects could raise atmospheric temperature in front of the asteroid to 100,000 degrees) and at these temps, the plasma formed would radiate in the X-ray range, irradiating the surface on every pass. Lots of fun to surmise all the radiation induced illness of critters on the surface(and, of course, a rise in mutation rates).

    Isn’t SciFi FUN?

    Gary 7

  58. bouch

    Nuts. I was hoping it would hit, and then I won’t have to worry about solving that nasty “unix time_t” issue which might become an issue in 2038. That’s going to be even bigger than the Y2K bug and the Myan calendar ending combined!

  59. @bouch: Glad I’ll be retired. (Haha! As if!)

  60. JoeSmithCA

    @Gary (#58)
    Wayyy to realistic for something like SyFy channel. It’d have to be a piece of a star that got knocked off by the collision with a blackhole. Require one scientist a nuke to fly solo up to the star to make it implode and disapear. Oh and of course during the whole time there would be tsunamis, floods, earthquakes and tornadoes–maybe some volcanoes if they can squeeze it in. See now there’s some kwality science ficshun for the masses.

    On the serious side, that’s an awesome idea. Seriously, you should write a story about it. :)

  61. ND

    I’m not sure if you want to play gravity tractoring with Apophis given how close it’s going to miss. Maybe nudging an astroid belt object would be a better idea. Maybe.

    But … :) I would be interested in impacting Apophis into the moon. that would be cool.

  62. ParrotSketch

    @#56 Eightman:

    “Yeah, great, except now there’s a possibility of impact in 2068.”

    A possibility of 1 in 9 Million. Big Deal.

  63. Paul A.

    So the odds are 1 in 250,000 that the asteroid will and… End Human Civilization?! At what point do we worry? If it is risk versus reward we should worry now. At what point does earth redirect all its efforts and wealth to solve an highly unlikely but utterly devastating event? Of course thanks to religion a large portion of the society would opt for doing nothing and just praying the problem away, or accepting it as god’s will.

  64. Gary Ansorge

    62. JoeSmithCA

    I started that story after your suggestion, then realized it would take WAY too much time to adequately develop the character interaction and since I’ve been writing another story for the last three months, I really have to concentrate on that one. I DID initiate the characters, some based upon people we all know and detest, such a an actress, named Jenny McKoont and her boyfriend, US President John Cloacus. Feel free to run with the idea and sell it to Syfy. I’m sure they can totally screw up the science if they try,,,

    Gary 7

  65. Joel

    what sort of satellites are 30 000 km away?

  66. Charlie in Dayton

    Does this mean there won’t be…

    …(wait for it)…

    …an Apophistrophe?

  67. Plutonium being from Pluto

    Ooops! Inadvertant double post deleted by its clumsy author.

    (Disaster postponed ..er prevented! 😉 )

  68. Plutonium being from Pluto

    @ 52. Naked Bunny with a Whip Says:

    @Plutonium being from Pluto: You added a word to my question, which was actually a tongue-in-cheek response to #31.

    Yeah, well my response to your response was pretty tongue in cheek humour too! 😉

    Added a word? All I can think of there is ‘Apophis’ in brackets – is that what you mean?

    @ Charlie in Dayton :

    Reminds me of a B-grade movie where at the end the main character heroine is given huge congratulations for “postponing” a major disaster! 😉

    (She actually prevented it from happening – a nuclear meltdown of some sort I think – but I swear they *said* ‘postponing’ which really isn’t that good!)

  69. 100,000 degrees that’s violet hot


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