Wocka wocka wocka Mimas wocka wocka

By Phil Plait | March 30, 2010 7:30 am

New data from Cassini were just released, showing a thermal map of Saturn’s "Death Star" moon Mimas. This map shows where the smallish moon is warmer than in other places, and can reveal a lot about its surface. The scientists expected to see it being warmest pretty much in the middle of the map, since the Sun was shining down on that spot at the time the map was made. As you go progressively farther from that spot, it would get cooler.

What they got, though, was this:


Um. That looks familiar. If the warm part eats that dot in the middle, will the other moons of Saturn turn into ghosts so Mimas can eat them and get points?

Anyway, on the left is the visible light view of Mimas, and on the right is the temperature map. Yellow is warm (well, 92 Kelvin or -290 F) and blue is cooler (77 K or -320 F). That’s not at all what was expected! The parts that should be warmest are actually cool, and the cold spots are too warm! Worse, perhaps, is the shape of the boundary. You’d expect a smooth transition from warm to cold, and it would be circular in pattern. Instead, we get this sharp, V-shaped thing!

It’s not known why things are so messed up on Mimas. Maybe the distribution of materials on the surface is uneven, causing an odd heating pattern. The warm spots might be covered in a material that is slow to lose heat (so it stays warm long after the Sun sets), and the cooler spots are covered in a material that is very slow to heat up (so they remain cool when the Sun is high in the sky). Maybe the cooler stuff is just coated with something that reflects a lot of heat from the Sun, so it never warms up. I imagine more temperature maps like this one, taken at different parts of the Mimas day, may help sort that out. Emily Lakdawalla at The Planetary Society has a far more in-depth description of this.

This map makes me very happy. Not because a gigantic PacMan hundreds of kilometers across is wocka-wocka-ing across a moon of Saturn (though that helps). It’s because this is a complete surprise. No one expected this! Now we have scientists scrambling to figure it out, and that makes scientists happy.

After all, folks, if we had all the answers, and no surprises were left, we wouldn’t call it exploration, would we?

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures

Comments (42)

  1. Chris

    It’s the energy emissions from the reactor in the center of the Death Star!

  2. Kurt_eh


  3. M-O-O-N, that spells Pac Man!

  4. Jim Shaver

    Honestly, if I had seen that picture elsewhere on the internet, I’d be sure it was a hoax, or at least a joke. I mean, come on, seriously?

  5. Mapnut

    Wocka-wocka-wocka : Ugh. How nerdy.

  6. Left_Wing_Fox

    I think the more we study, the more we’ll discover that Mimas is actually a large ball of memes created and placed by time travelling /btards. Give it 5 years, and our first extra-terrestrial contact sign will be from Mimas as well, s some cybernetic mad man proclaims that all our base are belong to them.

  7. AliCali

    Even though PacMan is the overall theme, what’s the over/under on number of Star Wars references in the comments?

  8. I thought you were channeling Fozzie the Muppet dog for a moment there!

  9. Rowlf was the dog, Fozzie was the bear. 😀

    I thought the same thing though.

  10. TheBlackCat

    Which direction is the moon moving? How much kinetic energy would impacts with debris from the rings or effects from Saturn’s magnetic field produce?

  11. Bigfoot

    I strongly suspect the Cassini group, or the originator of this (BA?), wants to make sure everybody gets their April Fool’s joke on time.

  12. Pi-needles

    @^ Bigfoot: If so, then they failed – it’s too early – still March here & everywhere else too. 😉

    Cool “warm areas” map. 😉

    I always have loved the “Death Star” moon & now I love it even more. 8)

    PS. BA if your idea of warm = 92 Kelvin or -290 F then I am definitely *NOT* jumping into your pool when you say the water is “warm.” 😉

  13. That’s really weird. Could it be something going on underneath? Geothermal activity or differences in tectonic plates perhaps? Just thinking out loud.

  14. Danno

    Just a thought but is the warmer side facing Saturn? Wikipedia is telling me that Minas is tidally locked.

  15. bigjohn756

    It’s Pock Man not Pac Man.

  16. Tim G

    You should have used the title “Pacmoon” or “Pacmoon Fever”.

  17. Charles Boyer

    The first thing that came to mind when I saw this was heat capacity variations, and when I decided to RTWA (read the whole article) I can see that Phil articulated that nicely.

    It looks rather like a macro version of some FLIR work I did a long time ago where the answer to “odd” results was exactly that.

  18. XMark

    Seems that the crater is right in the middle of Pac-Man’s mouth. Maybe when the meteor impact happened it hit with such force that everything in the middle of the moon got smashed off balance.

  19. AndyG

    Y’know, if you squint at the regular image, it’s possible to make out a second circular structure, also centred on the Death Star crater, but huge – so that its border is roughly where the jaws of Pacman are. Might be wishful thinking or … pacadoielia. 😉

  20. Pi-needles

    PS. BA if your idea of warm = 92 Kelvin or -290 F then I am definitely *NOT* jumping into your pool when you say the water is “warm.”

    Although I may grab my ice skates for your pool!

    Yeah, I know it is all relative. Except, that is, for *my* relatives who are absolutists! 😉

  21. Jya Jya Binks Killer

    Pac man’s been frozen into the Death Star? Now that’s cool! 8)

    @Andy G – If you are seeing what I’m seeing then I see it too.

  22. Tom

    ‘And I am both terrified and reassured, to know that there are still wonders in the universe, that we have not yet explained everything’

    G’Kar, Babylon 5

  23. Stan9FOS

    Silly humans. It’s obviously the result of the Giant Monolith, keeping its toes warm while waiting for Dave Bowman. (I know, wrong moon. Clarke couldn’t have gotten everything right, could he?)

  24. Impact point compressed the ground around the crater, causing it to have different thermal properties…

    That’s where I’m putting my money.

  25. Well, I gotta admit, when I read the title, I thought it was some 70’s porn reference.

  26. DrFlimmer

    That’s no moon!

    Yeah, it’s old, but still good, ain’t it?

  27. jcm

    pacmanedolia. Nice.

  28. Don

    As indirectly implied by XMark, the crater Herschel must have been caused by an object with a different density than the balance of the moon (or affected the density once things cooled down). This is affecting the heat release in this area, making it cooler than the rest of the moon.

  29. MadScientist

    The lines appear too sharp for that to be likely to be a difference in materials causing the effect. The image also seems to imply that there is a detectable atmosphere. As for the big pit, such seeming temperature differences may be purely imaginary and the result of the pit being a better effective radiator than the surface of the planet. Under some conditions there can be a genuine difference though – the pit will also be a better absorber of radiation than the general surface of the planet.

    One demonstration I used to do (back in the days when I did real science rather than – ugh – engineering work) was to show an audience two objects which were at identical temperatures. On a thermal camera one would appear very hot (because both objects were very hot), but one would appear pretty cold because it was a poor thermal emitter (so the cold sky in the background made it appear much colder than it really was) – however, plopping some bacon on the apparently cold object easily dispelled the notion that the object was cold. The same could be achieved by getting an unbeliever to touch the ‘cold’ object, but I’m told that’s unethical. Thermal images require substantial expertise to interpret; things are not always what they seem.

  30. Gary

    Right now Richard Hoagland is racking his feeble little brain to find a way he can use this as “proof” that aliens are everywhere, but without making himself look even more deranged than he already does.

  31. Russell Kramer

    With all the matter in the Universe its inevitable someone will find a cross or Virgin Marry on a planet or moon. I’m not looking forward to newspaper headlines on that day.

  32. If we had all the answers, and no surprises were left, we would call it “Climate Science”

  33. Peter

    “Honestly, if I had seen that picture elsewhere on the internet, I’d be sure it was a hoax, or at least a joke. I mean, come on, seriously?”

    Well, we are approaching April the 1st.

  34. bobbicus

    I, for one, welcome our new 80s video game overlords…

  35. ColonelFazackerley


    It’s a space station…

  36. The lack of communication within NASA amazes me.
    Surely the Cassini/Saturn/Mimas people talk to the Jupiter/Io people?

    A few years ago the Jupiter people identified that the volcano activirty on the moon Io, and hence the temperature and climate was dictated by the variations in the force of gravity from Jupiter & Io’s orbit..
    ie IO has an eccentric orbit, it gets closer (more force of gravity, more friction, more heat, lower gravitic Potential Energy (relative to Jupiter) more kinetic energy, and then further away (to result in less volcanic activity, lower force of gravity, less direct gravity friction ,less heat, larger PE and lower KE on Io, hence cooler when it is further away. At this dictance from the Sun solar insolation energy is trivial and does NOT matter.

    Then along comes Mimas, even further out, solar insolation is even less significant. The shape of the temperature profile is warmer closer to Saturn, (I assume- off to the left somewhere??) the largest source of gravity in the area.. The far side of Mimas (at the right) gets less gravity force, is further away and so has more PE (relative to Saturn) & less KE in it. It SHOULD be cooler. Isn’t night side Earth cooler than day side Earth which is closer to the major source of energy- ie gravity plus solar insolation?

    This idea that solar insolation is the sole source of energy on a planet is absurd. It is a simplification that obscures obvious conclusions.

  37. TheBlackCat

    PS. BA if your idea of warm = 92 Kelvin or -290 F then I am definitely *NOT* jumping into your pool when you say the water is “warm.”

    Although I may grab my ice skates for your pool!

    Except it would be like ice skating on a stone slab, if I recall correctly ice is not slippery at those temperatures.

  38. Marc

    I can’t believe you guys are taking this seriously… of course it’s an April Fool..!

  39. T M

    Re: John Dodds

    Good idea, also occured to me – except that the hot areas correspond almost perfectly to the trailing hemosphere of Mimas (on the picture it’s not entirely clear – the Herschel crater is at about 120 degrees longitude).
    It is actually unclear a the moment whether the cold region corresponds to the surrounding of the crater or to the leading hemisphere – more imaging from a different angle is required. It however visibly does not correspond to the side facing away from Saturn.

    tl;dr: Saturn is *behind* this image, not off to the left.

  40. ej

    It looks like a fish is being swallowed…


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