Phobos is, like, totally groovy

By Phil Plait | January 24, 2011 7:00 am

As recently promised, the European Space Agency’s Mars Express probe made a very close pass of the small moon Phobos, taking incredibly detailed pictures of the spud-shaped rock. Emily Lakdawalla, as always with planetary missions, has the what-fors with this event.

When it was a mere 111 km (66 miles) from the moon, Mars Express took this amazing image:

Click it for the full-res version is a whopping 7800 x 5200 pixel, 13 Mb TIF barsoomenated version. The detail is incredible, with features as small as 8 meters (roughly 25 feet across). Since Phobos is about 27 km (17 miles) long, that’s a lot of detail!

But as regular readers know, I have a thing for 3D red/green anaglyphs, and as the probe passed the moon naturally took stereoscopic images. The folks at ESA put two together to make this jaw-dropping 3D shot of Phobos:

Click it to get 3800 x 2600 pixel, 13 Mb TIF version. You really want to. If you have red/green glasses, this is one of the best anaglyphs from space you’ll see. I’ve never seen something stick out of my screen like this! Also, the details were so sharp that if I shake my head back and forth (like gesturing "no") I can actually see Phobos rotate a little bit, due to the change of positions of my eyes! That was new to me as well, and is very cool. it really solidifies the illusion that you’re seeing an object three-dimensionally.

Mars is an astonishing place, and it’s easy to forget how interesting its two moons are (the other is Deimos, which is smaller than Phobos). Their origins are still something of a mystery, and the surface features on Phobos are not totally understood either. Specifically, all those parallel grooves are pretty weird! The current thinking is that they were actually caused by impacts on Mars! It works like this: some giant rock hits Mars and blasts vast quantities of material up and out, some of which reaches up into space (Mars has a thin atmosphere and lower gravity than Earth). Phobos plows into this material, and the direct impacts with big chunks can form craters. But material from impacts on Mars is likely to be ejected in plumes (see, for example, rays around the crater Tycho caused by impact plumes on our own Moon). Hitting those would leave long, linear gouges in the surface. Grooves!

As incredible as it sounds, the evidence does point to this scenario; for example, a lack of grooves on the trailing part of Phobos, where ejecta from below couldn’t reach because of Phobos’ forward orbital speed (like how rain hits preferentially on a car’s front windshield and not the back).

Of course, hypotheses like this live and die on the evidence, so more data and more detailed images of Phobos are always welcome. Mars Express still orbits the Red planet and hopefully will continue to collect such evidence for a long time to come.

Image credit: ESA/DLR/FU Berlin (G. Neukum).

Related posts:

The shadow of a moon goes passing by
More incredible Phobos imagery
Phobos ahoy!
Phobos, up close and very personal

CATEGORIZED UNDER: Cool stuff, Pretty pictures, Top Post

Comments (37)

  1. thetentman

    What is the ‘S’ and dot in the lower middle of the picture? Has someone been there previously?

  2. Jamey

    A lot of the grooves look like something *ROLLED* along Phobos, to me!

  3. Allen Thomson

    How is it that Phobos, Deimos and other asteroidish bodies, even tiny Dactyl, are kind of roundish, though not perfectly spherical? Aren’t they way too small for their gravity to overwhelm their material strength, which is why larger bodies like planets are spherical?

  4. Cz-David

    Just spent 15 minutes trying to touch that rock. Try sticking your finger in the huge crater (do not push your finger trough the screen). This is so amazing!

  5. Practice

    thetentman: from link mentioned above: “The south pole is marked with a dot and an “S” inside the large crater near the center.”

  6. JWColes

    thetentman – The S likely marks the location of Phobos’ South Pole.

  7. Michel

    Every time ESA puts two together makes me proud to be European.

  8. Another amazing flyby by Mars Express! These pics are awesome! Phobos really has some crazy texturing on it. Does look like something rolled all over it.

    I put together a rotation animation from the five HRSC images that Express managed to get during its 9 seconds of exposure time with Phobos. I wish those were in 3D, now that would be cool!

  9. Andy

    I’ve recently read the novel “Impact”, by Douglas Preston. While not exactly 100% scientifically realistic, it involves Mars and its moons thru very hi-res images just like this one.

  10. Elias

    Obviously the “S” is the Phobos version of crop circles.

  11. MarkW

    Funny you should mention Barsoom, Phil. I woke up with a sore thoat this morning.

  12. Joseph G

    Ahhh – that explanation of the probe’s cameras (specifically the pushbroom cameras) in Emily Lakdawalla’s post on Planetary Society answers a whole lot of my questions! For one, it explains the odd image smearing in that other pic Phil posted showing Mars’ surface in the background. As well as a bunch of others about the way that these images are collected, how and why different color channels need to be added together, and other stuff.
    If you use Facebook, add her as a friend – it’s a great way to keep up on her blog, especially if you have one of the many, many Facebook tracking apps on your phone.

    Edit: YES, I know what RSS is. I’m incredibly lazy, so sue me.

  13. How about side-by-side stereogram images for those of us that don’t have the ol’ red-green glasses? It’s just as easy for me to replicate the 3D image by crossing my eyes just so.

  14. Keith Bowden

    @Andy – I read Impact last year as well. (I liked the book, but as usual with Preston, I have too many questions about things he didn’t go into – and not in a good way.)

    @Joseph – RSS is a tool. Facebook is another tool. To each his own!

    Phil – I’ll be supertharkamated! Thanks, this is fantastic!

  15. I have red and green glasses and the pic was spectacular! Thanks for posting it!

  16. NAW

    If the “What is the ‘S’ doing on the moon?” was a real question.

    “The south pole is marked with a dot and an “S” inside the large crater near the center.”

    Awesome picture, every time you post one of these I wish I kept the homemade red/green glasses I made for a class that one time. Then note I got to make another pair.

  17. Ross

    Is it possible that Phobos and/or Deimos are actually chunks of Mars that were lofted into orbit by an impact or some other cataclysmic event? What kind of forces would be needed to lift a 17-mile chunk of rock into orbit without pulverizing or vaporising it?

  18. Joseph G

    @#18 Ross: Well, the prevailing theory about our own moon is that it formed from the debris of an enormous impact very early in earth’s history, but of course we’re talking about mostly molten rock and gas, not single big solid chunks. I suppose it’s possible that Phobos and Deimos are simply small enough that they never achieved hydrostatic equilibrium (or were disrupted and never got it back). Their low density does suggest that they’re “rubble piles”, large rocks with gaps in between.
    The other hypothesis I’ve heard is that they’re captured asteroids, but that apparently causes its own set of problems, as their orbits are quite circular, not what you’d expect from captured bodies, and they don’t seem to match the mineral composition of asteroids, eitherm at least from what little data is available.

    In any case, the Russian Space Agency is launching a multi-national sample return mission to Phobos this year, so in the not-too-distant future, scientists will have actual pieces of Phobos to run through all their various scanning microscopes and gas chromatograph-mass spectrometers and such, so we’ll know a good deal more about it then :)

  19. Joseph G

    Also, does anyone know where to get red/green anaglyph glasses, cheaply? ūüėõ

  20. I’ve heard that Phobos is actually an ancient Martian spacecraft, a generation ship launched by Martians as their planet became increasingly uninhabitable. We know this because it’s filled with a vast network of interior spaces, which can only be living and engineering quarters.

    (I’m not saying I agree with this, just that I’ve heard it. ūüėõ )

  21. Ross, Phobos and/or Deimos wouldn’t have to be lifted into orbit whole, since gravity would cause debris to re-form into a moon over time.

  22. David Bibb

    Even with Red-Blue glasses it has amazing 3-D features.

  23. Joel Hall

    Phenomenal 3D image! I didn’t have good results with red/green glasses, though. Only with red/blue glasses. It is so interesting to think that rather than a CGI asteroid in a movie, this is real image of a moon in our solar system. Such an amazing time we live in.

  24. Messier Tidy Upper

    Groovy! ūüėČ

    Little Phobos flying high
    Yet still so low its doomed to die
    In millions years
    To Mars will crash
    A great new crater shall it bash!

    Into Mars will this moonlet slam
    This porous world won’t turn to jam
    But rather deep its hole will leave
    Will any remember it & grieve?

  25. Messier Tidy Upper

    @18. Ross :

    Is it possible that Phobos and/or Deimos are actually chunks of Mars that were lofted into orbit by an impact or some other cataclysmic event? What kind of forces would be needed to lift a 17-mile chunk of rock into orbit without pulverizing or vaporising it?

    Unless I’m mistaken – & I may be – that is, indeed, one of the current theories for explaining the moonlets origins.

    Like Earth’s Moon – and, for that matter, Pluto’s moons – the Martian satellites might be the results of “Big Splash” impacts throwing up material from the surface into orbit.

  26. Messier Tidy Upper

    For more on the origin of Pluto’s moons & Earth’s Moon – and maybe the moons of Mars too – see :



    NB. the Plutonian moons then known as P1 & P2 are now named Hydra and Nix. :-)

  27. Messier Tidy Upper

    Also via here :

    In fact, some scientists think Phobos and Deimos could be asteroids that somehow ended up orbiting Mars instead of crashing into the planet, or they could be leftovers from the time of planetary formation. Another option is that the moons are fragments of Mars, blasted off the planet’s surface by a large asteroid or comet impact.

    Confirming that idea – & also that the Martian moons origin remains uncertain.

  28. Digital Atheist

    Judas;… the stunning difference between the 2D and the Anaglyph when seeing both at thesame time is AWESOME! it shows how much we really miss being able to see things in 3D. wow. Thanks for the pics Phil.

  29. s

    I too think these 2 moons were once part of Mars. Mars looks to have the top part of it sheared off way in it’s past.

    Someday when samples from these moons are compared to Mars itself, that will be a monumental day.

  30. DreamDevil

    I wonder wich one of thoose craters houses the gate to Hell.

  31. These are excellent pictures!

    At this very difficult to believe that two different satellite captured rotate in one plane, even if we imagine that the fact that their orbits by the planet’s equator – just a coincidence.
    Most scientists are still inclined to believe that Phobos and Deimos – an asteroid, trapped in the gravitational capture of Mars. However, this theory, according to the University of Virginia Professor Fred Singer, is in conflict with the laws of physics can not explain why the two satellites moving around the planet for nearly circular and equatorial orbits. Periods of rotation around the axis of each of the satellites coincides with the period of revolution around Mars.

    See also:

    Artifacts on Phobos:

    Low density and the internal cavity of Phobos and asteroids:

  32. Doug

    Don’t give me that! I know what the “S” is! It is a marker left by aliens! It’s probably the first letter in the name of the Face!!!!!

  33. CharonPDX

    Anyone want to make a Nintendo 3DS-compatible .MPO file out of the 3D image? Red/Blue anaglyphs just don’t work for me, whereas the 3DS does.

  34. Chris Martin

    Most of those lines run back into that big crater on the end, (Stickney), so it seems obvious to me that the grooves are simply crater chains from that impact. The idea that they came from Mars itself seems most unlikely.


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