The raw face of the Death Star moon

By Phil Plait | February 15, 2010 10:45 am

Of all the moons in the solar system, Mimas is one of the most recognizable. And new pictures from Cassini show us again just why.

On Saturday, February 13, the Saturn probe dipped low over Mimas, sliding past the small moon at a distance of just 15,000 kilometers (9000 miles). For comparison, the Earth is about 13,000 km (8000 miles) across, so Cassini really threaded the needle with this pass.

On its way out from the encounter, when it was about 70,000 km (44,000 miles) from the moon, it snapped this astonishing shot:


Yegads. Note that this image is raw and unprocessed — it’s basically straight off the camera (and converted to JPG). But holy cow, there’s a lot to see. The giant crater Herschel is pretty obvious. It’s about 130 km (80 miles) across (compare that to Mimas itself, which is 400 km in diameter!), with a central peak characteristic of large impact basins. I think that’s where the main weapon is located.

cassini_mimas_herschelMimas has clearly had an interesting past: it’s battered beyond belief, loaded with impact craters. In fact, one thing scientists hope to learn from this pass of the moon is a bit of its timeline. By counting up the number of craters inside Herschel, and comparing that to the crater counts outside of it, they can estimate its age. Fewer craters inside of Herschel means it’s younger than the surrounding surface, for example. But how much younger? Maybe we’ll soon know. And they’ll be able to see craters that are pretty small; the resolution in the image here is about 200 meters (1/8 mile) per pixel. That’s about the same as we can do on our own Moon from Earth!

Sometimes with raw images like this, the background can be a little screwed up due to artifacts in the camera. But in this case, the glow on the left hand side of the big image is quite real: it’s the face of Saturn itself! The geometry of the shot was just right to capture a bit of the cloudtops of the ringed world. Very cool.

These are gorgeous pictures, and it’ll be nice to see them once they’re completely processed, too. We’ll learn a lot about the moon from them… and as far as Mimas goes, I just hope it’s not fully armed and operational. I suppose I shouldn’t be too worried though. After all, I used to bullseye womp rats in my T-16 telescope, and they’re not too much bigger than Mimas.

Image credit: NASA/JPL/Space Science Institute

CATEGORIZED UNDER: Astronomy, Pretty pictures
MORE ABOUT: Cassini, craters, Herschel, Mimas

Comments (54)

Links to this Post

  1. That’s no moon « Not So Fast | February 16, 2010
  2. Feed Proxy NEW AND IMPROVED or something. « Unspeakable Evil | February 20, 2010
  1. AliCali

    Wow. The edges are so sharp, so in focus, and so nicely framed that I first thought it was a model hung up with string inside a classroom.

    Were any pictures taken when the probe was closer to the 15,000 km distance? Can it even take pictures that close, or would it be a blur as it zooms by? Or perhaps it’d be closeups of the surface instead of this nice shot with the entire moon in one frame.

  2. It will also be interesting to see if Mimas’ surface turns out to be older than Callisto’s

  3. Noooo! You cut off a bit of the left edge! We’ll have to take this one again! Mimas, could you take a step to the right? Err, left. Your left.

    That is so sharp it looks fake. Amazing!

    …I think what makes it look “fake” at first glance are the shadows in the upper left, shadows that seem to be cast by the moon on a background surface. But on closer inspection, it appears that these shadows are being cast by Mimas on itself! That’s some terrain! If the Earth’s surface is (as I have read in a book somewhere, possibly one of yours) smoother than a billiard ball (if you were to scale the Earth down to the size of a billiard ball, its surface features would be on the order of the sratches and dings in a billiard ball), I wonder how smooth Mimas is?

  4. Charlie

    I’m wondering about the Herschel crater. Wouldn’t an object large enough to create such a large crater relative to the size of Mimas the have fractured the moon itself or have at least created some noticeable ejecta across the rest of the moon? It looks very neat, like the effects of the impact were confined to the impact crater itself. I hadn’t thought about this before seeing this picture (and, no, I haven’t googled for the answer yet – too lay-zee/biz-ee).

  5. ScottW

    In other news, AT&T lays claim to Mimas, citing intellectual property rights, and prepares to launch robotic probes equipped with thousands of gallons of blue paint…

  6. Greg in Austin

    That’s no moon. Its a space station.

    I’ve got a bad feeling about this.


  7. Greg in Austin

    I can imagine one of the Cassini engineers here on Earth programming in the flight pattern:

    Engineer: “Keep your distance, but don’t look like you’re keeping your distance.
    Cassini: “Beeep?”
    Engineer: “I don’t know. Fly casual!”


  8. Thought that was a Styrofoam Mimas Deathstar Hybrid just based off the thumbnail I saw before visiting this blog post, hehe. :) That’s awesome.

  9. What an amazing shot! It does look like a model at first glance.

  10. DrFlimmer

    @ AliCali:

    Exactly my thoughts as well! Nice model! 😉

    @ Greg in Austin:

    Well put! 😀

  11. Joe Meils

    400 km in diameter… the original Deathstar was supposedly about 200 miles in diameter… Obviously, the Empire is sticking with it’s “build ’em bigger” design philosophy.

  12. Jim

    Apparently there’s stress fractures from the impact that can be seen on the opposite side of the moon.

  13. kevbo

    My God! You shoot small animals for fun? That’s the first indicator of a serial killer, you freak!

  14. In response to Charlie: the moon must be made out of some highly dense material to stay intact.
    Since Cassini’s launch Cosmologists have stuned the world with actual images of the solar system.

  15. mike burkhart

    Ther is only one problem with calling Mimas the Death star moon the crater Herschel is near the equator of mimas on the Death Star the super laser dish was on the uper part of the station the resion was so the dish could be aimed by rotateing the top part ( I know that was not shown in the movie but has been in some of the star wars books and comics )

  16. r00b

    Looks like a sable cookie. 😀

  17. andy

    Now the interesting question is why Mimas is apparently ancient and battered, but Enceladus seems to be quite an active environment, with geysers and smooth plains (evidence of resurfacing). Mimas is located closer to Saturn than Enceladus, and its orbit is more elliptical, both factors that should lead to more tidal heating.

  18. mike burkhart

    One more thing the book 2001 a space odysey had the Discovery going to Saturn and as it approched the moon Ipetaus it discoverd a large white spot with a small black spot in the middle of it that turns out to be the monolith when Voyager photograpth Ipetus it showed a large white spot wiht a black spot in the middle only it did not discover any monolith may be sometimes science fiction gets some things right

  19. drow

    it LOOKS like a model, because it IS a model! if you look close at the pixels, you’ll see that they’re the same pixels that NASA used to fake the moon landings! they didn’t even bother filing off the serial numbers of some of them!

  20. Oli

    @mike burkhart – Did it really show that? I thought only a big white face, not the black spot in the middle.

  21. John Paradox

    Meanwhile, on the ‘dark side’ of the moon……

  22. @mike burkhart #16: You’re thinking too 2D. You have to be able to aim “up” and “down” as well as “left” and “right”.

    On a more serious note, I’m really curious about the scalloped edges of a lot of the craters.

  23. Jason B.

    Seriously. It looks like a miniature. Crazy.

  24. Magic_Al

    @mike burkhart as you’ve probably noticed, in the original Star Wars movie, the version of the Death Star plans downloaded from R2D2 actually shows the superlaser dish being positioned on the equator, so Mimas resembles that image. The graphic inconsistency had to be left in the movie because of how long it took to create the then-groundbreaking computer animation. I always thought it would have made the most sense to have the dish at one of the poles, or a dish at each pole, because it would be aligned with the power core, and the rotation of the entire station would stabilize the aim.

  25. JB of Brisbane

    Did I hear someone say, “Commence primary ignition”?

  26. Wayne on the plains

    I know this joke’s been made already, but I wanted to say that I teach astronomy, and every time I show a picture of Mimas, I can’t resist muttering “That’s no moon…” A few kids usually get the reference.

  27. andy

    So when does dredging up “that’s no moon…” and various other Death Star references every time Mimas is mentioned get as annoying and tedious as all the stupid jokes associated with the name of the 7th planet from the Sun?

  28. Aaron


    By the way, Greg (#8), classic, my friend.

  29. AliCali

    @ Andy: When do Star Wars references get as annoying as Uranus jokes? Never, so long as the jokes evolve and improve, as in Futurama:

    Astronomers changed the name of Uranus to end that stupid joke once and for all. Now it’s called Ur-Rectum.

    Of course, I notice that very few of the Star Wars jokes here have evolved, but true evolution could take many, many years. I’m sure there’s an X-Men joke to put here, but I’m only a minor nerd.

  30. Greg in Austin


    You’re right, the jokes do get old. Luckily, some of us never do!


    Don’t be so proud of this technological terror you’ve constructed. The ability to [photograph] a planet is insignificant next to the power of the Force.


  31. Bigfoot73

    Anybody notice the similarity between the huge impact basin and that on Saturn’s other death star, Iapetus?

  32. @ Andy:

    I find your lack of faith in geek jokes disturbing…

  33. Gary Ansorge

    15. Ernie M. Brewer

    The estimated density of Mimas is 1.17, which would seem to indicate it’s mostly water and a little bit of rock however, I wonder how such a soft mix could retain such sharp edged craters AND survive such a massive impact as the Herschel crater?

    MAybe it really IS hollow,,,

    GAry 7
    PS: OMG! We’ve found our generation ship. I wondered where I parked it.

  34. Messier Tidy Upper

    “Lord Vader, I’m afraid there’s bad news about the Death Star. You know how you said they were spending too much money on heating and you insisted they turn it down a bit?”

    Tor-Ssssssh breath FXT thingy. “Yes?”

    “Well now it’s frozen solid, my lord! Totally!” 😉

    Is this what you get when you combine a “snowball Earth” with the Death Star? 😉

    See :

    Seriously, that is one awesome picture! 8)

    Thanks Cassini team & Dr Plait. :-)

    If that’s not on the BA’s “Top 10 for 2010” well … I’ll be very surprised.

    @ 36. Gary Ansorge Says:

    15. Ernie M. Brewer : The estimated density of Mimas is 1.17, which would seem to indicate it’s mostly water and a little bit of rock however, I wonder how such a soft mix could retain such sharp edged craters AND survive such a massive impact as the Herschel crater?
    Maybe it really IS hollow,,,

    That idea could also apply to Phobos one of the moons of Mars according to a recent ‘Astronomy’ magazine article speculating about caverns within it. This was also proposed in an SF short story by Arthur C. Clarke for one of the moons of Jupiter. (Amalthea before it was named as such & just known as Jupiter XI or something like that I think ..)

  35. Messier Tidy Upper

    Okay, with a few minutes research on Wikipedia I’ve found exactly what I was thinking of – just too late to beat the editing countdown clock :

    The SF short story I was thinking of was ‘Jupiter V’ and, yes, that’s what Amalthea was called then.

    See :


    As for the caverns of Phobos mentioned – Oops! Afraid I gave y’all the wrong source for that – sorry, mea culpa. :-(

    The article I was thinking of there was “Cheap Flights to Phobos” in New Scientist 30th January 2010 :

    During the flyby’s, Mars Express’s High Resolution & Stereoscopic camera mapped the surface of Phobos, which led to the most precise 3D model of the moon so far and a measure of its volume. … “The mean density is unexpectedly low. It must be a porous body,” says Patzold. So rather than being a single vast chunk of solid rock, there are probably vast caverns inside the moon which could shelter future visitors formthe ravages of space radiation.

    Hmm .. Potential for a few SF ideas there too! 😉

    See more on Phobos wikipedia page here :

  36. DrFlimmer

    @ Greg in Austin

    I never get tired of the Star Wars references! Your last one was extremely hilarious and it cost me two minutes to breath again. The force almost choked me 😀 .

  37. I absolutely love shots like that first one. I really gives the feeling of a true solid object that I could reach out and pick up off my monitor. 😀

  38. Joe

    LOL at the Star Wars references

  39. Another thing obvious from this picture is that the Mimantean surface is highly reflective. We tend to think of other worlds as being rocky bodies like Earth, but in fact what most often functions as ‘rock’ as we know it in much of the outer Solar System is in fact water ice! Most images of Outer Solar System bodies are low-enough resolution that all one sees is a bright surface with some craters and other features — nothing to give a feel for what that surface is made of. But in this one, the way that the surface in that amazing image reflects light does look like it is a smooth hard shiny surface like ice. Neat!

  40. Wow. It’s as smooth as a golf ball. Loving this image! I want more.

  41. Calli Arcale

    Bigfoot73 @ 34:

    Anybody notice the similarity between the huge impact basin and that on Saturn’s other death star, Iapetus?

    Iapetus additionally has this awesome equatorial ridge. Okay, it’s kinda the reverse of the Death Star’s trench, but visually it works very well. 😉

    Actually, gargantuan impact basins are frighteningly common in the Saturn system. Mimas has one, of course. Iapetus has one. (Well, several, actually, but one is more prominent than the others.) Tethys has one, though it’s more slumped, giving the moon more of an eyeball appearance. Rhea has a whopper too. Titan, Enceladus, and Dione are the only large Saturnian moons which appear to lack such a scary-big crater.

  42. Oh the Star Wars jokes NEVER get old. Come on now. 😉

    When the image is rotated so north is up and south is down…you know, like in the real world [wink]…it REALLY looks like a certain evil empire’s space station. (Check it out here: And yes, a collision like that probably very nearly did blow the moon apart…there’s fracturing on the other side of Mimas from the force of it. Perhaps it was still somewhat hot and melty when it got hit, or perhaps its water ice composition helped it absorb a big impact better than something more dense and rocky. Who knows. But it’s a cool moon, and the images from Saturday’s flyby are fantastic…great post and kudos to the Cassini team!

  43. Steve F

    Those are not crater impacts but the points where electric plasma bolts grounded to the surface by passing near a highly charged object. Note the raised center in the middle of the depression, the same pattern when duplicated in a plasma lab of a strong electric charge grounding itself out on a dirt,rock like surface. Google “Electric Universe” which as a working theory that has successfully predicted all the anomalies that the gravity model always fail to do, like with comets. A theory is only as good as it is able to predict future discoveries that the gravity model totally fails to do with comets and other space phenomenon. Heck the gravity people have to go to massive mathematical construct and make up things like black holes and strings which have never been proven or will be to keep propping up a bad theory. Be a leader and not a follower. Many thought washing hands prior to surgery was nuts but we now know different. Are you stuck in the past? Do you only get grants for supporting the status quo or are you a true explorer of knowledge? At least check it out with an open eye. I doubt this will get published, can’t offend the gravity sucks modle.

  44. Nice try on poisoning the well there, Steve F (#47), but I prefer people who have blatantly antiscience views to be making their statements in public for all to see. The Electric Universe “theory” is based on gross misunderstandings of basic physics, which is the actual reason scientists for the most part ignore it.

  45. Red 2

    Look at the size of that thing!

  46. Red Leader


  47. Aaron

    @Steve F (#47):

    Remember, the Force [of gravity] will be with you, always.

  48. Carter

    Gravity does have trouble fitting in with the quantum physics model (so far)… And it seems that these problems arise not because we do not know what particles transmit quanta of gravity (gravitons) but because we do not have a complete grasp on why particles have mass, and such a wide range of masses at that. Be a leader and not a follower, help discover the Higgs boson (or other working alternative)!

    But, really, general relativity is a powerful model of predicting what gravity does to things. It works. Do your physics homework.


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