3 D House of Comet Nucleus!

By Phil Plait | November 9, 2010 7:15 am

Via Emily Lakdawalla at the Planetary Society Blog is this amazing 3D animation of the EPOXI spacecraft’s close approach to the nucleus of comet Hartley 2!

You’ll need red/green glasses to see it in 3D, but if you prefer the folks at EPOXI HQ put together a nice flat version:

Incredible! Also at Emily’s blog is an awesome size comparison of various small solar system bodies like comets Halley and Tempel 1 (which EPOXI took a close look at in 2005 when it was still called Deep Impact). The nucleus of Hartley 2 is actually pretty dinky compared to the other comets, but note how similar in shape it is to Halley and Borrelly. Clearly, two-lobed peanut-shaped nuclei are not rare among comets, and even though we’ve only gotten a close look at a handful of them, I’d even wager they’re downright common! That surprises me, and I am not at all sure I understand why that shape is prevalent.

We see it in asteroids like Hektor and Kleopatra, and those may be due to two small asteroids having a slow collision and sticking together. I’d think that’s unlikely with such small objects as Hartley’s nucleus, but the evidence suggests otherwise. I will be very curious indeed to read some papers on this.

The more we look at the Universe — and the more closely we look — the weirder and more wonderful it gets.

Related posts:

The depth of space
3D Apollo
More *incredible* Phobos imagery
Opportunity for anaglyphs

CATEGORIZED UNDER: Astronomy, Pretty pictures

Comments (27)

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  1. Chris

    If Hollywood put a peanut comet like that in the movies, people would say it doesn’t look realistic. It’s amazing what nature can dole out.

  2. The size comparison with the International Space Station was interes….OH MY GOD IT NEARLY COLLIDED WITH THE SPACE STATION!!!!!

  3. Messier Tidy Upper

    @ ^ Kuhnigget : That’s nothing – you should see what it did to the Shuttle! 😉

    @1. Chris : Yes, truth is stranger, again. Although I’d say Hartley 2 is shaped more like a chicken drumstick or bone for a dog .. 😉

    Marvellous work by Emily Lakdawalla here once again. The 3D one looks great even without the glasses. :-)

    If Emily’s doing requests then I wonder how it looks versus a space shuttle and the Apollo CSM-LEM craft & Saturn V to scale?

  4. fred edison

    Wow! Any explanation as to why Hartley 2’s center section appears so smooth in the photos while the rest is cratered and irregular as you’d expect from encounters with other space debris?

    Awesome stuff with the active outgassing evident. It may be small compared to other comets but it’s putting on an incredible show. “Good job” to all involved with capturing these fantastic images.

  5. @1. Chris: yeah no kidding…..anything headed on a collision course with Earth would have to be all nasty-looking, dark and spiky and full of hissy steamy geysers….’cuz only clearly EVIL things would want to kill people! Yahh! Get ’em!!! *pewpewpew*

    Now peanut……peanut would never hurt ANYone.

  6. Wilson

    I was struck by how similar it is to asteroid Itokawa.

  7. Joe Alvord

    Could a comet’s close approach to the sun combined with it’s miniscule gravity pull it apart at closest approach and then have the two parts drift back together like two snowballs stuck to each other?

  8. Messier Tidy Upper

    @ ^ Joe Alvord : Pull it apart? Definitely – that’s happened to quite a few most famously Biela’s comet in 1846. Coming back together, well, not so probable! 😉

    Once split I think the comet would stay split and likely disintegrate further.

    @5. J. Major :

    Now peanut……peanut would never hurt ANYone.

    Unless they’re allerguic to peanuts! 😉

  9. Messier Tidy Upper

    See : http://en.wikipedia.org/wiki/Biela%27s_Comet for more on what happens when a comet is split in twain!

  10. MattF

    MTU: I wonder how it looks versus a space shuttle and the Apollo CSM-LEM craft & Saturn V to scale?

    The Saturn V was 363.0 ft. (110.6 m) tall. The Shuttle stack is 184.2 ft. (56.1 m) tall. Comet Hartley 2 is described as about 500 m wide in the “short” direction. Should be pretty easy to figure.

  11. MaDeR

    “Any explanation as to why Hartley 2’s center section appears so smooth in the photos while the rest is cratered and irregular as you’d expect from encounters with other space debris?”
    Contact binary. Two bodies rotating close to each other. Dust and rock gathers between them in strange gravitationally place exactly between two bodies and accumulate. Result: peanut!

  12. Jeff

    yes, it even looks like that model comet Phil whipped together on his latest Bad Universe show. Looks scary when you see it is a 3 -D big ice/rock like right down here on earth!

    I can see why that impactor extinguished dinosaurs and other life forms.

    probably the spikes are so prounounced due to the weak gravity of this cometary nucleus

    I think they had better develop a technology like that finesse tug to get Apophis away from that keyhole. No sense taking a chance it would hit earth. That one does concern me.

  13. Damn…I need to find my anaglyph glasses…

  14. Dragonchild

    Phil –
    Methinks you might be approaching this comet shape problem from the wrong angle. Two small asteroids in a sticky collision sounds particularly unlikely, even more so if it was common. ADDING material sounds unlikely for something well-known to shed mass.

    Now, I have no evidence to base this off of, but isn’t this a question of how comets eventually become that shape after many of years of wear & tear? Also, a common shape would need to develop from a wide variety of initial conditions — in other words, the model needs to be convergent. The answer is to figure out how any random roundish or potato-shaped dirtball winds up looking like a peanut. A comet’s most intense experience is the perihelion, but if they truly are the solar system’s leftovers, even the long-period comets have had a lot of close encounters with the sun since the birth of the solar system. Is there some way to simulate what happens to a tar-covered snowball as it swings by a nuclear-powered furnace a few hundred times?

  15. QuietDesperation

    Hmm… the video needs a sound track.

    Now peanut……peanut would never hurt ANYone.

    Allergies aside, of course.

  16. Reverend J

    Tried it with the 3D glasses and wasn’t particularly impressed. I don’t think they separated the colors enough to get a good feeling of depth.

  17. Tom K.

    When I first saw this I thought it was a cell in the reproductive stage of splitting in two. After gathering debris from around the Solar System to have enough to make more comets? Probably not alive though.

  18. Buzz Parsec

    Low-density peanuts? It’s left-over packing material from the crate the solar system came in.

  19. Jeremy Thomson

    Dragonchild: I’ve got to wonder if perhaps the comets outgassing combined with a little spin might get to the peanut shape. Comets will tend to spin with the axis perpendicular to the orbit. This would be reenforced when they approach the sun. The face nearest the sun wants to rise in orbit the side away wants to drop. So the comet will have a warm equator and cold poles. More outgassing at the equator and gas will be flung by the centrifigal force. Vapour at the poles has an easier time reconnecting and refreezing and there may be some migration of vapour from the equator to the poles. If this happens I would expect the poles to be ice rich and the equator to be carbon rich. Carbon enrichment at the equator would absorb more light, outgas more the result is a hour glass shape.
    Thats my hypothesis, Its purely my uninformed speculation. Someone tell me how I’m wrong.

  20. Mark Hall

    You may think that’s a terribly large comet, but it’s peanuts to space!

  21. 13. Christopher Duvall Says: “Damn…I need to find my anaglyph glasses…”

    Don’t bother. It seems to move too quickly for the eyes to adjust to the moving colors, at least for me. I got more of a 3D effect from the motion of the image without the glasses than from the anaglyph with them.

    Does anyone have a feel for the time scale of the other flyby video? It passed really close so that angular speed was probably not too exaggerated.

    – Jack

  22. rob

    i checked the contents of that 3D video and it is made of 100% awesome–no filler.

  23. John Brewer

    One possibility for the shape is collisional fusion (http://arxiv.org/abs/0911.5398). Essentially two rocks slam into one another with sufficient energy to melt the surface between them but not entirely break apart. As they rebound away from one another, the melt re-freezes causing the two rocks to stay stuck together.

    It is a pretty neat solution to one of the outstanding problems (getting from cm sized particles to kilometer sized rocks) in planetary formation theories.

  24. Lee Holmes


    The mission to Hartley 2 is EPOXI; the spacecraft is still Deep Impact.

  25. Messier Tidy Upper

    @ ^ Lee Holmes :

    Thanks for clearing that up, was wondering about that myself but not sure. :-)


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