Jupiter: bringing the hammer down

By Phil Plait | July 23, 2009 1:00 pm

One thing I’ve leaned over the years is that the Universe goes on, even if you’re at Comic Con.

In this case, I think we can say beyond any reasonable doubt that Jupiter suffered a major impact recently. I was wary at first, and maybe still wavering a bit even later, but now there’s no question at all. Why? Because of this image from the giant Gemini North telescope:

Gemini image of Jupiter impact

Bang! We’re done arguing. This image was taken at 18 microns, well out into the infrared where what you’re basically seeing is heat. There are spots and things on Jupiter’s cloud tops that are visible, but the impact feature in the center of the frame is obvious.

Hubble image of SL9 impact scar

The reason I’m so sure now is that this looks almost exactly like the images returned after the comet Shoemaker Levy 9 broke into dozens of pieces and repeatedly slammed into Jupiter 15 years ago. Here’s a Hubble image (right) of that event for comparison. You can see the the splash pattern is just the same, indicating the trajectory of the incoming debris.

Some people have asked how you can get a feature like this when Jupiter has no solid surface. That’s a fair question! The impactor is probably a chunk of rock or ice a mile or so across. It’s moving very quickly, probably at 100 or so km/sec (60 miles/second). That gives it a HUGE amount of kinetic energy, that is, energy of motion. Still, as it passes through the upper atmosphere of Jupiter, where gas is thin, not much happens.

But as it drops down the air gets thicker, and at those speeds the pressure on the incoming rock is enormous. As the gas in front of the meteor compresses, it heats up a lot, the same way a bicycle pump heats up when you use it. But in this case the gas gets heated to thousands of degrees, and glows. The pressure on the rock starts to flatten it out (scientists call this "pancaking"). The rock starts to break up, and then each one of those pieces compress and heats the air in front of it, pancakes, and breaks up, forming even smaller pieces, and so on.

In a few seconds, this cascades into a vast amount of energy released essentially all at once. That is what scientists call "a whopping big explosion" (sorry to get technical on you here). So you don’t need a physical impact with solid ground to get a detonation, you just need lots of pressure, and that’s easy to come by with Jupiter and things falling on it from space.

And that’s why we see this huge impact scar. The explosion vaporized the incoming rock, and that debris blasted upward and rained down on the cloud tops, discoloring them. It also carved out a giant hole in the clouds, revealing lower atmospheric layers in early pictures, and blasted up material from lower down as well. This debris can float on the cloudtops for weeks and months, which is what happened in 1994 with SL9.

I have a lot more details about all this in the first chapter of my book, I’ll add.

Remember, too, that this event was spotted after it was all over and all that was left in the visible light images was a black spot… and also remember that this was spotted by an amateur astronomer! Astronomy is one of the few fields where unpaid but extremely capable people can make a huge (no, I won’t say "impact") contribution. Congrats to everyone involved for catching this rare event early enough to make more observations and detailed scientific analysis possible!

Image credits: Imke de Pater (UC Berkeley), Heidi B. Hammel (Space Science Institute), Travis Rector (University of Alaska Anchorage), Gemini Observatory/AURA; NASA.


Comments (59)

  1. Travis

    Is it possible to do some sort of spectral analysis to figure out the chemical composition of the impacter and possibly determine if it was a comet or a stray asteroid?

  2. AliCali

    So 4.5 billion years after our solar system’s formation settled into planets, we’re still getting objects running into each other. It amazes me to think of how many impacts there must’ve been billions of years ago when there were so many more of these rogue pieces of rock and ice floating around our solar system.

    It also makes me gracious for big ‘ol Jupiter taking the brunt of many of these instead of us!

  3. CW

    Just to confirm, there was no “impact” but rather the object began to disintegrate and then exploded? At what point did it transition from “pancaking” to “whopping big explosion?” I’ve never read or heard about this phenomenon before, so do meteorites (or other objects) do this when they fall to Earth?

  4. This event seems to have unleashed a round of “if we didn’t see that coming then we’re DOOMED!” on the Internets, ignoring the fact that hitting Earth is like hitting the center of a bull’s eye to Jupiter’s barn door, not to mention the difficulty of spotting mile-wide asteroids at distance of 4-6AU.

    (The recent glut of dreadful “meteor” TV movies probably doesn’t help!)

    We have already greatly reduced the odds of being caught out by an asteroid or comet, and those odds are only going to get smaller and smaller over the next few decades. Indeed, when our descendants look back at this time, they’ll probably identify a period of no more than 100 years in human history when we knew about the threat from above but we’re unable to do anything to prevent it from happening.

    They’re going to have much more difficult natural threats to defuse — caldera volcanoes like Yellowstone, and undersea landslides (like the Big Crack in Hawaii) for starters.

  5. rpsms

    @#3: Yes, airbursts happen, AFAIK, Tunguska event was an airburst, rather than an “impact”

    I am curious why it is “pitch black” in the visible spectrum. Ash?

  6. Lawrence

    Given Jupiter’s size, location close to the Asteroid field, and gravity well – I’m surprised this doesn’t occur more often.

  7. I tried to observe the spot with the 26″ Clark refractor at McCormick Observatory the other night, but Jupiter was swimming in the summer atmosphere and too indistinct. The summer planets are low in the night sky for the same reason the summer Sun is high in the daytime sky. This is why the Aussie fella who found this thing had an advantage on us folks up here in the North. He had it high in his winter sky and easy to photograph clearly.

  8. dhtroy

    I have no idea why it is, when I see stuff like this I think “That’s so cool”, but it is just amazing. Leaves with me a sense of wonder about the Universe, realization of how little we know and excitement that we’re part of this massive, complex and incredible system; and I can’t wait to see what we learn next.

  9. GA

    Thanks, Phil, for the explanation of the “impact” on a gas planet. I was explaining the new spot to my 7-year old and he stumped me with this question. I admitted to him that I didn’t know the answer (no harm in that, right?). Now I know, and will try to explain it to him.

  10. Buzz Parsec

    Yup, we’re all in a Doom. If the biggie hits in the ocean (75-80% chance), then tidal waves will destroy everything except a few mountain tops. Your only hope is to sell everything you own and move to the top of a large mountain. Just transfer the deed for your house and the title to your car and all your bank accounts to me, and I’ll sell them for you on Ebay and contribute all the proceeds to charity. (Might as well make everyone else’s few remaining days a little happier.) Just make payable to the Buzz Parsec Foundation for a Better Buzz, and I promise to get a better Buzz.

  11. What`s this book he keeps raving on about, aboutÉ

  12. justcorbly

    @#4 Tacitus: “The recent glut of dreadful “meteor” TV movies probably doesn’t help!

    Did you see that two-part miniseries called “Meteor” that NBC just ran? Man, did that smell! Some kind of nonsense about little asteroids hiding behind each other. And, of course, we wait until the first enters the atmosphere before we try to nuke it with a barrage of missiles. Then, a cute scientist with a laptop calls in with retargeting info so that another barrage of nukes deflects the second rock out of the atmosphere and away from the Earth.

    Made even less sense than the other recent flick wherein a chunk of a brown dwarf sneaks up on the Moon with no one noticing.

    When I’m in the mood, I can forgive the inaccuracies. After all, it’s just a comic book with real actors. But, man, that NBC effort was such a sloppy job that I feel sorry for the cast. They should’ve sued to get their names off the credits.

  13. Jearley

    There was a great interview with Anthony Wesley, the amateur astronomer who discovered the impact. The interview was broadcast on NPR this morning, and is available here:


    rpsms: You asked about the dark color of the impact area. During Shoemaker-Levy, the explanation was (if I remember correctly) that there were chemical reactions due to the heat of the impact that caused carbon compounds to form from methane, CO2, and other gases in both the impactor and the Jovian atmosphere. I do not know if this was confirmed, or remains a hypothesis.

    CW: Yeah, objects do this in the Earth’s atmosphere too. The Tunguska event is a good example.

  14. Al Seever

    I was amazed when comet Shoemaker-Levy 9 hit Jupiter. To have two impacts during my life is just so awesome. Glad it wasn’t the earth though…

  15. John Phillips, FCD

    @Buzz Parsec, your post gave me a right buzz :)

  16. Torbjörn Larsson, OM

    At what point did it transition from “pancaking” to “whopping big explosion?” I’ve never read or heard about this phenomenon before, so do meteorites (or other objects) do this when they fall to Earth?

    The way that was formulated reminds me of the water drop photos circulating on the web today. Researchers have been able to capture falling water drops for the first time – and the larger ones “pancake” (to an inverted “bag”) and then rips apart in a “whopping big explosion” (for their scale) before hitting their terminal velocity. This presumably explains water drop size distributions.

    [Though I won’t decide if it’s the correct model before I’ve seen a predicted distribution tested against the actual measured.]

    So it is perhaps a somewhat universal first order response to falling fast enough in an atmosphere.

  17. Gary Ansorge

    With material splashed up from deep in Jups atmo, I wonder what a spectral analyses of those gases might tell us about the atmospheric structure of Jupiter. If there IS a solid surface beneath the clouds, night not some of that also have been blown to the surface where we could analyze it?

    GAry 7

  18. I’m just amazed that an amateur astronomer had the time to catch this, given all those alien spacecraft they must be spotting.

  19. pontoppi

    Just a teeny correction: According to the Gemini press release, the color image is a composite of 8.7 and 9.7 micron images, selected from images spanning 8 to 18 micron. These filters were presumably chosen because ground-based mid-IR images can be (nearly) diffraction-limited, so the resolution is better at 9 micron than at 18.

    In any case – I’m loving this!

  20. CW:
    Jupiter is all atmosphere, so by definition all impacts will vaporize and/or break up in the atmosphere.

    On planets with solid surfaces with atmospheres, small objects decelerate (and heat up) in the atmosphere, but large ones punch through and hit the surface.

    As a result, these planets have minimum crater sizes, where all impactors smaller than a certain size burn up, and thus don’t leave a crater. Thicker atmospheres have larger minimums, so on Mars it is a few meters, on Earth it is around a hundred meters, and on Venus it is several kilometers.

  21. Jearley

    When Shoemaker Levy 9 impacted, Carbon disulphide and Ammonia were detected in the in the impact scars. There were also some heavy metals found, but I have not been able to find an explanation of the dark coloration. Anybody have info on this?

  22. angelo

    @Lab Lemming

    well, actually Jupiter does have a solid core… probably… deeeeeep down…
    but to crater *that* you’d need a “****ing whopping big” impactor! 😉

    you’ll find everything you may want to know (and a few things you might not) about meteorites and airbursts in “Rain of Iron and Ice” by John S. Lewis

    by the way…
    many thanks to Mr BA for the reading advice in the BA book :)
    for “Rain…” obviously, but mostly for “A Candle in the Dark” — I rediscovered Carl Sagan with tis book (Cosmos had me glued to the TV set when I was a kid) and it’s really a joy to read…

  23. Stone Age Scientist

    Hi Phil, I could be wrong but I seem to have heard from recent news that Anthony Wesley also made his own telescope. I’m not so sure what the reporter meant by the word ‘made’ since the news just glossed over Mr. Wesley’s discovery, and also gave some tidbits of info about the astronomer. Note: I may have heard the whole thing wrong, but if it is indeed true, then we are looking at a truly remarkable man.

    I hope Mr. Anthony Wesley sees this entry and tells us if I’m just imagining things up, or if it’s really true that he made his own telescope.

  24. «bønez_brigade»

    The SL9 pic kinda resembles the Hubblesite.org logo (like, maybe, just a little fraction of a bit).

  25. Robert


    Why is the spot black?

    If I had to make a guess…
    The light we see from jupiter is sunlight reflected from various clouds (vapor droplets…) The impact released such a large amount of heat that most of these clouds evaporated, leaving translucent gasses. So basically the meteor punched a translucent column through the atmosphere, the dark color you see is the shadow of the edges of this hole (or you could just say its deep enough that its dark at the bottom.)

    Just my hypothesis, I’m certain a few of you guys can probably think of something better.

  26. @Stone Age Scientist, #22: It’s not uncommon at all for people to make their own scopes. I built my first one out of parts and a bunch of wood, but there are people who take the time to grind their own mirrors and lenses by hand as well as fabricate other pieces like focusers, mount gears, etc. Google “Amateur Telescope Making”

  27. DrFlimmer

    As long as those Amateurs creat better mirrors than the one on Hubble, everything’s fine ;).
    Speaking of Hubble. I read on spaceflightnow.com that Hubble, although not yet finally configured after the SM, will take a look at Jupiter. Photos are probably available on Friday (today).

  28. As long as those Amateurs creat better mirrors than the one on Hubble, everything’s fine ;).


    Although it was probably the most precisely figured mirror ever made, with variations from the prescribed curve of no more than 1/65 of the wavelength of visible light…

  29. Martin Moran

    Our solar system is so cool! Jupiter probably helps us out much more than most realise.

  30. Jeff

    a good illustration of the mechanical equivalent of heat. For every joule of kinetic energy (energy of comet motion) Jupiter’s atm. will absorb about 0.25 calories of heat energy.

    If comet is 1km radius, it would have kinetic energy approx. 1 X 10(20) joule which is
    about 25,000,000,000,000,000,000 CALORIES dumped into Jovian atm., which is a lot of heat

  31. ND
  32. Harbles
  33. Bob

    One wonders if having seen two major Jupiter impacts in their lifetime, TPTB might be having a “Aha!” moment and start to seriously think about putting real money/effort into either detection technology or habitats in orbit. Personally, I’d love to see the Kepler mission provide us a list of “earth-like” planets within a 30 LY radius and the proverbial lightbulb goes off and the migration off Earth begins….

    Of course, those pesky FTL and artificial gravity problems need to be adressed first, but hey…the Wright brothers didn’t design an F-22 right off the bat either. Baby steps.

  34. HEADS UP!

    From a friend’s LiveJournal – http://dr-nebula.livejournal.com/790428.html

    Apparently there’s an outside chance his last-before-impact images of Jupiter might actually have caught the fireball!

  35. Stone Age Scientist

    drksky @ #25 and DrFlimmer @ #26,

    Have you peeps seen the telescope Mr. Wesley used when he discovered the Jovian dark spot? I’m not an expert on telescopes, but I can tell you it is not your average telescope . The diameter of the thing was more or less as big as a barrel and twice as long.

    I was somewhat hesitant when I posted entry # 23, and I’ve been trying since yesterday to find the news where I heard that particular story. I may have heard it on TV, or seen it in the internet; the thing is, I forgot. I was so busy at work the last few days that these matters slipped through my mind. Anyway, this is all I have, from a Sky News article entitled Amateur Tells Nasa: ‘Comet Hit Jupiter’, (or Google this string anthony wesley homemade telescope),

    Evidence suggesting Jupiter was struck by a comet has been found by an amateur astronomer using a home-made telescope….

    Again, I have no idea how “homemade” Mr. Wesley’s telescope is; but judging from the Birds Astronomy site, I’d say this is not entirely impossible. And look, he even used Gimp.


    Btw, correction for entry #23, the word I should have used is ‘built’ and not ‘made,’ which is misleading. Have a nice weekend, guys.

  36. From the picture that I saw on The Independent, it’s entirely possible that telescope is homemade. It’s only 14.5″ which is very much in the realm of hand-grinding. The tube looks like it was fabricated out of sheet metal.

    Believe it or not, that is a very average scope for a dedicated amateur. Newtonian reflectors are very cheap per inch of aperture and probably the most popular designs for larger scopes.

    Without speaking to the man himself, I’d have to say, yep, he made it (as opposed to just built it).

  37. Greg in Austin


    hubblesite . org/newscenter/archive/releases/2009/23/
    Not bad for incompletely calibrated equipment.

    Go Hubble!


  38. Flying sardines

    Awesome news. 8)

    Like others I’m amazed we’re witnessing another actual impact so soon after comet Shoemaker-Levy-9.

    I wonder whether it would be possible to detect the impacting object on old photos – now that we know to look for it & we can calculate its approximate position and orbit – or can we?

    Might the impactor have been spotted but mistaken for one of Jupiter’s many small moons or moonlets or a background star – much like Neptune was spotted several times incl. by Galileo without people realising what they were looking at?

    One final thought – if it is discovered and a bit is learnt about it, might this impacting body be “posthumously” named for Mr Wesley? Posthumous for it not him natch! 😉

  39. Greg in Austin


    No, that’s why we’re NOT seeing UFO’s. We’re too busy looking at small areas of the sky. 😉

    Now, if only one of those Alien Spacecrafts (that we don’t know exist) flown by Aliens (that we don’t know exist) would be kind enough to pass thru and hover around my field of view…

    Oooh, maybe it was a UFO that hit Jupiter, and not something ordinary and boring, like a comet. Perhaps it was a big black monolith. It is almost 2010, afterall.


  40. Plutonium being from Pluto

    Do we have any idea of exactly how far down the impactor went before it finally exploded?

    Could it have detonated where the denser atmosphere of Jupiter transforms into an ocean of hydrogen or even metallic hydrogen?

    Can we use spectroscopy to tell how much of the dark material in the black spot that resulted was from the impacting object and how much from lower levels of Jupiter’s atmosphere or ocean?

  41. Hey, I’m glad to see you mention it and to confirm that there really does seem to have been an impact event. I’m glad because I first heard about it from Hoagland (who’s preparing a “major piece” about it); I like the guy and I’ve followed him and Mike Bara for a long time, but you’re the reality check at times like this (those guys may be wrong about some things, but at least their ideas never hurt anybody!). Hyper-dimensional implications aside, I look forward to your further prosaic commentary :)

  42. Nevy C

    The Hubble image looks like an ear-less polar bear with one eye. Or maybe it’s an earless winking polar bear.

  43. (those guys may be wrong about some things everything, but at least their ideas never hurt anybody!)

    There. Fixed that for you. 😀

  44. just an *old* heads up for more pics: http://www.nasa.gov/mission_pages/hubble/main/jupiter-hubble.html <– hubble has pics of the aftermath =)

  45. Actually, drksky, didn’t Phil once praise Richard and Mike for the work they did debunking the claims of the moon-landing-hoax crowd?

  46. The New York Times ran a story today about Jupiter’s Dark Spot. Instead of talking about why Jupiter is hit more often than the Earth, the article is abotu whether or not Jupiter is out “cosmic protector”. Furthermore, in the print version of the article, the headline was “Maybe Something Up There Likes Us”.


  47. @Jon Lester, #50: Ok, I do remember hearing RH say something backing up the Apollo landings, so yeah, maybe they got that one thing right…

    I spent an eternity one afternoon on Hoagland’s site and it made my head just about asplode. Never been back nor really listened to anything he’s said.

  48. Charles J. Slavis, Jr.

    Darn! I thought I saw my first black hole.

  49. Charles J. Slavis, Jr.

    Before CERN starts making miniature black holes, I want to patent a black hole trash compactor. You would never have to take out the trash again. Just don’t get to close to it.

  50. Charles J. Slavis, Jr.

    If I am repeating myself, see my comments on evolution in multi-dimensions.

  51. Mark

    As the gas in front of the meteor compresses, it heats up a lot, the same way a bicycle pump heats up collector-solar.com when you use it. But in this case the gas gets heated to thousands of degrees, and glows. The pressure on the rock starts to flatten it out

  52. Kaal

    I took my family to a Planetarium ( Johannesburg, South Africa ) on Saturday 25 July.
    I was pleasantly surprised when the presenter told the impact story ( including how NASA was still busy calibrating ), and then showed the original and the Hubbard images.
    Definitely not a “canned” show !

    She also talked quite a bit about how people see what they would like to see ( the canals on Mars, the head on the moon etc.)

  53. pyrolyte

    jupiter saves!


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