More *incredible* Phobos imagery

By Phil Plait | March 31, 2010 7:32 am

I’ve already posted some beautiful closeups of Phobos, a moon of Mars, taken by the Mars Express space probe, after the European Space Agency aimed the spacecraft at the tiny moon. The closeups are beautiful, but now the ESA has posted a stunning full-body shot of Phobos:


[As usual, click the pix to embiggen.]

The resolution is an amazing 9 meters (30 feet!) per pixel. Clearly, Phobos has been through a lot. Mars orbits near the inner edge of the asteroid belt, which may explain how battered its surface is. The grooves were once thought to be ripples from a big impact that created the whopping crater Stickney (not seen in this view, but you can see it really well here), but are now thought to be from boulders rolling around in the low gravity of the moon, perhaps ejected rocks from various impacts landing back down in the feeble gravity.

Note the one winding path going from the upper left to lower right: that looks very much like a boulder bounced its way across the surface! The curvy path is an indication of the changing gravity field of Phobos: it’s not a smooth sphere, but a lumpy potato, so the surface gravity — what you’d think of as "down" if you were standing there — changes greatly depending on position.

phobos_anaglyphThey also put together this stunning 3D anaglyph. You can really see the depth of the craters and grooves on the surface. Run, don’t walk, to get a pair of red/green glasses for this one! Phobos really pops out of the screen. The depth and clarity of the 3D is amazing!

This pass of the moon was designed to obtain as much scientific data as possible before the launch of the Russian mission called Phobos-Grunt, which will land on the moon and send a sample of its surface back to Earth for study. Phobos looks an awful lot like an asteroid itself, and its origin is still something of a mystery. More data like these — and obtaining a sample of its surface material! — may clear up its story once and for all.

Credits: ESA/DLR/FU Berlin (G. Neukum)

CATEGORIZED UNDER: Astronomy, Pretty pictures

Comments (47)

Links to this Post

  1. Phobos, A Martian Moon | Surprising Science | April 2, 2010
  1. Chris

    Wow, just like Avatar except without the blue people and plants.

  2. Kees

    I think Phil forgot to close a [subscript]-like thingy. The whole blog is messed up

  3. Plutonium being from Pluto

    What about Deimos? Isn’t the Mars Express taking any photos of Mars other moon? 😉

    Great image & write up tho’. :-)

    @2 Yep. I’ve tried to close it here using [/sub-script] only brackets.

    Has it worked? Nup? :-(

  4. SionH

    I wonder if you could play it like a wax cylinder?

  5. Pi-needles

    @1. Chris Says:

    Wow, just like Avatar except without the blue people and plants.

    LOL. 😉

    And I don’t recall “Pandora” looking so small & cratered either.

  6. Gary Ansorge

    Phobos also has a “monolith”, an upright blob of material and it’s right next to a crater. The shadows thrown by both are classic examples of the difference between shadowing a crater vs a mountain.

    I wonder if it’s more a comet remnant than a true rocky asteroid? If so, then the Russian Grunt will give us compositional data which we can compare to our other comet analyses.

    If it WAS a comet, it stands to reason there will be caverns inside, as the volatile materials evaporated over time. Great place for astronauts to hang out while observing MArs.

    Gary 7

  7. Jason Dick

    Well, I grabbed this source off of Wikipedia:

    This seems to be claiming that the grooves are actually strings of closely-spaced impact craters of matter ejected from impacts on Mars (they can’t be secondary impacts from stuff that struck Phobos because the escape velocity of Phobos is 3m/s. I don’t entirely understand how matter from an impact crater would end up spread out in a thin, nearly uniform line by the time it strikes Phobos, but it would explain these grooves.

  8. TaoMacGuy

    Random factoid of the day: If you weigh 150 pounds on Earth, you’d weight 1.4 *ounces* on Phobos! Lose weight now, ask me how!

    Also makes me wonder if I were to jump “up” on Phobos, how long it would take me to come back down (and yes, I’m too lazy to do the math 😉

  9. Pieter Kok

    TaoMacGuy, I’m not going to do the maths for you (you lazy bum 😉 ), but the escape velocity is 11.3 m/s, or 40 km/h. That’s a lot higher than I expected.

  10. Phobos-Grunt….хихикать!

  11. TaoMacGuy

    @Pieter… actually, I prefer to call it “busy”…

    [jon lovitz]Yeah, that’s the ticket. I’m way too busy right now to do the math. That’s it![/jon lovitz]

  12. JHem

    Wow, just like Avatar except with actual interesting content, besides the ginormous glamour of being in “3D” 😉

  13. Any chance of getting side-by-side stereograms rather than red/blue stereograms? The side-by-side ones can be viewed with the naked eye, with a bit of practice, and the results are much better than the red/blue ones (you can even do them in colour)!

    Also, I don’t have a pair of a red/green *or* red/blue glasses. Let alone a pair with the right polarity.

  14. Pi-needles

    @ ^ David Given:

    Also, I don’t have a pair of a red/green *or* red/blue glasses. Let alone a pair with the right polarity.

    If you had got the wrong polarity ones you could just reverse the polarity & all would be fine. 😉

    Well, if the world worked the way Star Trek / Dr Who does.

    I’m supposed to be “busy” right now .. but I’ve decided I’ll give up procrastinating tomorrow instead! 😉

  15. BJN

    I don’t buy a resolution of 30′ per pixel. The image has banded noise horizontally and diagonally and the quality of a given pixel isn’t high enough to accurately represent terrain at the particular gray value it’s showing. At actual pixel resolution you can easily see the noise. Zoom in and you can see that individual pixels are too noisy to represent real surface detail. Compared to recent NASA imaging, it looks like the ESA images aren’t nearly as high quality (assuming that NASA isn’t doing destructive noise reduction to make images look better).

  16. Alex


    Based on a human being able to jump about 2 ft on Earth, I work out a hang-time on Phobos of about 5-10 minutes.

  17. DaveS

    Hey, Doc, where locally (Boulder area) can I buy a pair of 3d glasses? I really don’t want to pay for shipping.

  18. Jya Jya Binks Killer

    I’ve been looking hard but I can’t see any portals to Hell, imps, cacodemons or spiderdemons anywhere there.
    You sure that’s the right moon? 😉

    Or do we need to wait for the LHC to work properly for those to appear before we’re DOOM-ed? Unless we happen to be BFG & chainsaw armed space marines of course! 😉

  19. XMark

    Are we gonna get a high-res shot of the monolith?

  20. IBY

    Huh, I thought it was a picture of the potato in my kitchen. Someone is spying on me!!!! *paranoid shaking of head*

  21. Buzz Parsec

    Darn SionH, I was working out an elaborate post saying how it was really one long continuous groove with wobbles and if you converted it to audio, it would come out as “Mary had a little lamb, it’s fleece was white as snow…”, but you beat me to it! :-)

  22. Jaz

    @David Given

    No need for 3D glasses. This nifty little program (StereoPhoto Maker) can display anaglyphs as stereo pairs:

    I’m about a third through HiRISE catalogue. Still no aliens or Bigfeet…

  23. First time I ever saw an image of Phobos I knew those lines were produced by boulders bouncing along the surface in low gravity. I realize the scientific method needs to beat around the bush a bit, but some things are just obvious.

  24. These pictures had already been published through ESA and DLR outlets two weeks ago – i.e. just five days after they were taken, which is very fast for HRSC imagery – as links in my respective blog entry show. Also the ‘captured asteroid’ hypothesis is no longer taken seriously in the community, as the density of Phobos has turned out to be way too low: One popular hypothesis now is that something collided with a pre-existing moon in Mars’ orbit, and Phobos reassembled as a hole-filled rubble pile from the debris – the latter insight was presented this month at a physics conference in Germany and is based largely on earlier Phobos fly-bys by Mars Express.

  25. Is Phobos the moon you can escape its gravity with a bike and a ramp? Or is that Deimos?

  26. Kristind

    I’ll just use the 3-D glasses I “stole” …er….ummm… didn’t recycle after watching Alice in Wonderland in 3-D.

  27. Allen Thomson

    Phobos grooves: Any chance they’re due to tidal stresses?

  28. MadScientist

    But what’s the thermal infrared image look like? :P~

    I hope the Russian mission to retrieve a sample works well. No more lens caps dropping in the wrong places!

  29. Joey Joe Joe

    How did they decide where the “north” pole is? Can a chunk of rock that size possibly have a magnetic field of any detectable strength?

  30. NelC

    Joey, I think they define it by axis of spin. The North pole is the one from where the body appears to spin anti-clockwise.

    On the grooves, I question how they could all be caused by wandering boulders when they mostly fall into nearly parallel groups. There’s the largest group that go around the body from Stickney to the other end, then there’s another bunch at the top of this pic that also seem to be parallel to each other. Also, the wandering track is actual craters rather than grooves. I can’t see that being caused by the same mechanism as caused the grooves.

  31. Petrucio

    The more you keep converting units for the SI impaired out there, the longer it will take for it to be widely adopted.

    In a science themed blog, shouldn’t it be about time imperial measures get kicked out the door for good?

  32. alaskana_98

    I always wondered what the horizon would look like if you were standing in at the bottom of that gouged out area on the left (a little to the right of the pointed tip). Would it still be a relatively flat horizon, or would it be all warped due to the fact that the moon is not an even sphere?

  33. Stupid Newbie here…
    Is this a black and white image or is Phobos really grey?
    It seems so ….well drab.

    Those martian folk should paint it or something. Maybe we could send some paint up with the Russian probe.

    Seriously – I wish every space picture would come with a little color guide, so I could tell what the colors mean and as in this case tell me if this is true color or just a b&w image.

  34. DLC

    Ah ha! they must be Phobian (Phobosian ?) Canals, from back when the Lizard Men lived there! 1!! /ufo-conspiracy

    Really cool imagery though. thanks for posting it Phil.

  35. Kevin Bartlett

    What would cause the boulders to roll along? Tidal forces from a nearby massive object, perhaps? I guess this wouldn’t explain that interesting track of craters, though…

  36. bk_2

    So far, the ideas for the origin of the grooves have been less than believable.
    1. “the grooves are actually strings of closely-spaced impact craters of matter ejected from impacts on Mars ”
    2. “boulders rolling around in the low gravity of the moon”
    3. Phobos is a chunk of sedimentary rock and the grooves form along strata.

    None of these stands up to examination.

    I propose a new idea. Isn’t it obvious? They are the tracks of rings. Phobos ploughed through a set of rings edge on early in its existence. No other mechanism could give rise to those long sublime trenches, straight as Roman roads right along the flanks.

    Rings, what rings? There aren’t any rings around Mars now. But then rings are thought to be transitory phenomena, Saturn’s rings may not be all that old. And anyway, Phobos must have knocked them to bits if this is what happened.

    I propose that Phobos and the rings were formed in the same event. Either a capture of an asteroid, or an impact on the surface which threw up a lot of material. If it was a capture I have to plead that the material which went to form the rings was dislodged from the original asteroid (or its partner if it was a binary system) by tidal forces on a close pass, below the Roche limit. If it was an impact there would have been plenty of stuff left over after the main body coalesced, to from rings.

    Either way, the debris must have settled down into circular and planar orbits relatively quickly, through collisions. But the main body would have had an elliptical orbit which circularized more slowly.

    The important consequence of both possible origins is that the orbits of the rings and the main body would be coplanar. During the period when the orbit of the main body was elliptical and the rings more circular, proto-Phobos would have intersected the rings at high speed on each pass at periapsis. With its tidally locked orientation presenting the same face to the flak each pass, you would expect to see the grooves starting on the leading face and continuing down the flanks, and none on the trailing face. A series of passes a few kilometers higher or lower would create parallel families of grooves.

    Of course there is the difficulty that the grooves, and families of grooves, are not all equatorial and cross eachother. In fact just south-west of the crater Drunio (?) there is a field where they cross at right angles. The stratigraphy is tantalizing. One of the best grooves in the picture goes north-south, skirting the N pole. If it was the result of of intersection with a narrow coplanar ring, Phobos must have been turned through 90 degrees around its direction of travel since the the groove was created.

    For these difficulties, I have to propose that the mass of the main body was altered so that the tidally locked minimum shifted. Perhaps Stickney was the cause. However there is one groove that extends into Stickney’s interior. It must have been laid down since Stickney. And thank goodness, it seems to be roughly equatorial.

    The crux of this theory is the shape of the grooves. Bouncing boulders leave me cold, but a ring edge on, maybe ten meters thick, of dust and sand, coming in at kilometers a second, would do it. A cosmic buzzsaw sandblaster. It doesn’t look like there was much exchange of mass, the ejecta would have escape the feeble gravity, but it would have exchanged momentum, helping to circularize the orbit of the main body.

    I put this idea up on UMSF some weeks ago and it was well-received, but it doesn’t seem to have got out into the wild. Let’s hope this generates some discussion.

    BTW it’s called the “ring-whacker” theory.

  37. BigBob


    On the grooves, I question how they could all be caused by wandering boulders when they mostly fall into nearly parallel groups.

    From a comment I posted previously:-

    Phobos (and as it happens Deimos too) is tidally locked with Mars, that is to say it always shows the same ’side’ to Mars just as our Moon always shows the same ’side’ to the Earth. So tidally locked moons rotate once on their axis for each orbit around their planet. That means Phobos has a leading face and a trailing face as it orbits Mars. So if the current theory about the grooves being caused by debris thrown up from massive impacts on Mars is correct, that explains why the many grooves are in parallel. The rocks that drew the lines would not have had to arrive all at the same time. Even if Phobos encountered a rock in its path today, it would still roll the rock along its flank and the groove that it made would be in parallel with hundreds of existing grooves. The fact that there are other ‘families’ of grooves on Phobos suggests that it used to be oriented differently, when its leading ‘face’ was not that part of the surface that leads today.

  38. P@J

    I like the ring hypothesis. The problem I see with the bouncing traction-suspended rock hypothesis is that many of the grooves seem to cross craters of signficant depth without changing geometry. Wouldn;t rocks bouncing along the ground come to a pretty abrupt stop in a crater (or fly right over without grooving the base, since gravity is so low).

    The sedimentary layering hypothesis belies the size of the damn thing: those would be some pretty big duneforms (note cross-cutting relationships), or if we are suggesting unconfromities, then we would expect some indication of changing rock type, wouldn’t we?

  39. WJM

    Duh! Those striations, Phobos is OBVIOUSLY a glacial erratic!

  40. Mau

    Wow it looks like a rendering from a shooter game. Either we are getting good at game graphics, or the universe out there is full of surprises :-)

  41. No you fools, they’re not geological things at all.

    They’re landing strips for alien spaceships!

    (Yes, it had to be said)

  42. Chris Winter

    I too questioned the posted theories about the origin of those grooves. BigBob’s clarification makes sense, except for one thing: the grooves on the upper surface of Phobos run perpendicular to the other, larger set on the near face.

    Of course, it’s possible Phobos’s orientation is chaotic; that its axis of rotation shifts from time to time… or that one of those impacts flipped it to a new orientation, leading to the two sets of grooves.

  43. Mark

    Did the boulders sink?

  44. Right angles…

    Glacial erratic comparison is interesting but check out the right angles.

  45. zhuyh

    The resolution is an amazing 9 meters (30 feet!) per pixel. Clearly.

  46. James

    Looks like a captured comet. That would explain the voids and its appearance.


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