Apophis ad Absurdum

At some point you've probably been driving down the freeway when a bug splats itself on your windshield. Did the impact send you careening off the side of the road? I thought not. But that's the underlying premise of a ridiculous story that took the Internet by storm yesterday.

Apophis and Earth in 2029
On Friday the 13th in April 2029, a 1,000-foot-wide asteroid named Apophis will pass close enough to Earth (within 20,000 miles) to briefly appear as a 3rd-magnitude star in the night sky.
Dan Durda
It seems that a 13-year-old German student chose a study of near-Earth asteroids for his entry in a prestigious science-fair competition. While crunching the numbers for a 1,000-foot-wide asteroid named 99942 Apophis, he discovered that the giant rock might strike an orbiting satellite when it brushes within 18,000 to 20,000 miles of Earth on April 13, 2029.

That possibility, the student concluded, had been overlooked by NASA's top dynamicists, and it increased the chance of Apophis crashing into Earth itself on a subsequent pass in 2036 from 1 in 45,000 (NASA's estimate) to just 1 in 450. It's a harrowing prospect — if he had actually been correct.

The story first appeared on April 4th in Bild, the German equivalent of Weekly World News. "I have calculated the end of the world!" screams the headline "...and NASA says, I'm right." This silliness might have died quietly, had the Agence France-Presse not repeated and embellished the tale on April 15th.

Kudos to German science writer Daniel Fischer, who got to the bottom of this mess and yesterday exposed it for the farce (or hoax) it was.

First, the boy misunderstood the flyby geometry in 2029 — the chance of striking a satellite is "vanishingly unlikely," NASA scientists insist. While it's true that Apophis will pass closer than the altitude of geosynchronous satellites, it'll be well outside them when it crosses Earth's equatorial plane, where they're located.

Second, Apophis has an estimated mass of some 20 million tons. Even if it did have a head-on collision with a sizable satellite, the impact would barely affect the asteroid's trajectory. (If you don't believe me, just ask the bug.)

16 thoughts on “Apophis ad Absurdum

  1. Bug's Revenge

    I wouldn’t necessarily discount an alteration of the asteroid’s trajectory, no matter how small. Even “barely affecting” the trajectory could be sufficient to nudge it into Earth’s orbit after it has traveled millions of kilometers. Tiny changes add up over time.

    But it does seem like NASA has accounted for a satellite collision and that this is just a hoax.

  2. Tom

    Bug, better to do the math involved in this collision before introducing a variable of unknown quantity (the collision) into the discussion. And so, playing the role of the hypocrite, collisions of this magnitude are far more likely during its travels in the solar system as the surface of any asteroid will attest. Our energies are better spent bashing the French for their role in trying to make NASA look bad.

  3. Enrico the Greqat

    This is why I roll my eyes over every asteroid impact story. The threat of impact of course is real, BUT the sensation loving scientifically illiterate mass media can not help but axagerate for the purpose of one upsmanship. The public looses out. This danger needs to be addressed by the scientific, political and military communities of the major world powers, but fear mongering and sensationalism will not help in this debate.
    The various Astronomy magazines, which are run by people who should know better do not help when they run sensational cover art in the genre I call “Impact Porn”.

  4. Sean

    its funny how you downplay aphosis. its actually 390KM wide not 1000 feet. you should do your research before you post a story. Secondly

     

    I’m not sure what came secondly, Sean, but as far as the size of Apophis, I’m on pretty firm ground. If it were really 390 km across, as you state, it’d be the fifth largest asteroid inside the orbit of Jupiter . . . and I can assure you it’s not. — Kelly Beatty

  5. Enrico the Great

    This is why I roll my eyes when I read about asteroid impact. Though the danger is real, media misinfornmation and sensation does not help public discussion of this very real danger. The scientific, political and military sectors of the major powers of the world must consider what actions to take if this possibilty becomes real, but the media have learn how to RESPONSIBLY report on this and other scientific questions. Sensationalism helps no one, in the long run even the media itaelf is hurt by it as people loose trust in it. So, lets stop the impact porn!

  6. Graham

    Well, I remember 7/4/06, when a large asteroid was supposed to pass by at well beyond 243k/Km, but while watching the shuttle launch that day on CNN and on the web through Nasa’s website, I noticed on the website, a female astronaut with a video camera who was recording the fuel tank separation, panned out and caught a view of the HUGE asteroid noticeably very close, much closer than they predicted! I looked for archived video from Nasa and found none. It seems she made a mistake, but I saw it with my own eyes and I wonder if anybody else saw it.

  7. Angus Crome

    Even if the asteroid was 390Km wide, seeing it at 18K-20K miles would roughly be equivalent to seeing that bug from you car at 0.75 miles. You have a better chance of seeing the Shuttle in normal space flight with your naked eye than that.

  8. James Durbano

    Apophis has been estimated to be between 270 m and 390 m in diameter, not 390000 m (390 km)! It would appear that Sean needs to “get the facts right” before he posts a comment. Also, for those of you who are “metrically challenged” 270 metres is more-or-less equivalent to 886 feet and 390 metres is more-or-less equivalent to 1280 feet. Therefore, reporting Apophis to be a 1,000-foot-wide asteroid is certainly acceptable.

  9. Jeff Stevens

    Kelly, I enjoyed reading your article. It’s good to know that we can rely on Sky & Telescope to present the facts so clearly and concisely. I loved the car windshield and bug comparison – it puts it into perspective beautifully.

  10. Dave

    I disagree that the bug/windshield analogy is a good one.

    The kinetic energy of a collision has less to do with the mass of the satellite (or bug) as does the relative velocity. Anyone who has been struck by a bullet should know that, as should anyone who saw what a small piece of foam did to Columbia. And these are relatively low velocity collisions.

    If you search the web for “Apophis” and “kinetic energy impactor” you will see reports (attributed to NASA) that a 1 ton object can deflect Apophsis’ path enough to move its path 31 inches a day, or 1 mile over 3 years.

    Thus, I believe the impact will be more than a bug on a windshield. The kinetic energy of the collision is 1/2 m v*v; that is, it is proportional to velocity squared. I’ve read that v will be 28,000 MPH or 12,500m/s. Square that and you get some pretty big numbers; the kinetic energy of a 4600kg satellite (ie.. Sirius 4) at that velocity relative to the asteroid is about 3.6E11 Joules. However, these are far from elastic collisions.

    Of course, the odds of an impact altering the path in exactly the right way so that it causes a collision (or orbital capture) are pretty slim; it seems that an impact will more likely decrease the chance of a collision, and as noted, at 20,000 miles away, the chance of satellite collision is almost nil.

    I would like to have seen a more scientific refutation of the article, with realistic calculations.

  11. Patrick@Denman

    Far be it from me to imply that most online and print media could not use some education – or at least more care in how they publish stories – but in following the thread of comments in this column, is it really any wonder that this story was so excessively exaggerated? Between the misquotes of the asteroid’s size and the debate over the significance of a collision and the mathematics involved, this is hardly the sort of calm, rational discourse on a volatile issue that demands it.

    I know that most of us are regularly horrified at misinformed reports like this one. But those of us who feel we may have a more balanced view should take the time for careful explanation, along with some level of understanding about how people tend to arrive at their conclusions. We need to build bridges, not walls.

  12. Mark Looper

    The commenters who express concern about the numbers involved (Bug’s Revenge, Dave) should click on the link at the words “vanishingly unlikely” toward the bottom of this article; it leads to a NASA page that discusses all the sources of uncertainty in the orbital predictions that were evaluated. The bottom line for this discussion is in the “Update Note” dated April 16th at the bottom of the page, which is where the “bug on a windshield” analogy appears to have originated. Even an impact with a big satellite at the 2029 flyby can only change the geometry of the 2036 flyby by hundreds of kilometers, whereas the uncertainty in that geometry due to such things as differential heating, gravitational perturbations from other than the three largest asteroids, etc. (the “known unknowns”) adds up to over 30 million kilometers. That’s not to say that even a “vanishingly unlikely” satellite impact, if it occurred, couldn’t change a few-hundred-kilometer miss in 2036 into an impact, or vice versa; rather, what NASA is saying is that the putative uncertainty added by the possibility of such an impact doesn’t significantly add to or subtract from the uncertainties already in the calculation, and certainly is not going to change the odds of a 2036 impact from 1 in 45,000 to 1 in 450 — from 1 in 45,000 to 1 in 45,000.0001, maybe.

    By the way, Graham — many stargazers saw the asteroid you mention, right where it was predicted to be. There’s a movie on this website at http://www.skyandtelescope.com/observing/highlights/3422556.html shot by one such observer. Are you sure you didn’t see a lens flare or a cloud or something?

  13. Reinhard

    Dave, you mentioned that the scenario is far from elastic collisions. So, the kinetic energy balance is irrelevant here as the colliding objects will heat up significantly. mv^2/2 is probably not at all constant, but mv always is. And that may make quite a difference which anyone who wants to experience it, is invited to play both Boule and Billard and compare the behavioure of the balls. 🙂

    IMHO, using the web as a reference may not be the best way to estimate asteroid deflections, even if the quotation is from NASA. I do not want to appear impolite, but I am always anmazed how many “experts” on the web feel encouraged to post estimates on scientific scenarioes that the professionals may have better tools for. To me the web is not really a reliable source of information.

    Finally, the point of the article was not that no major asteroid might collide with earth in the next couple of decades. The article was about how obvious hoaxes (“Bild” is very well known here in Central Europe) are forwarded and reprinted in an unreflected way. This example should make us concerned about how information is dealt with and perceived by “reliable” media and eventually by the audience.

  14. FER

    Ok, Dave. Calculate the kinetic energy of a mosquito impacting a car in the frame of reference where the mosquito is at rest. Next calculate the kinetic energy of a satellite impacting asteriod Apophis in the frame of reference where the satellite is at rest. Which one is greater? HINT: the fact that they are EQUAL and both ZERO is normal. I suggest this comparison only as a lesson in basic physics. Better analysis, upon request.

    -FER

All comments must follow the Sky & Telescope Terms of Use and will be moderated prior to posting. Please be civil in your comments. Sky & Telescope reserves the right to use the comments we receive, in whole or in part, and to use the commenter’s username, in any medium. See also the Terms of Use and Privacy Policy.

COMMENT