It's rabbit^h^h^h Phobos season!

By Phil Plait | January 12, 2011 7:00 am

The European Space Agency probe Mars Express has been orbiting the Red Planet for just over seven years now, returning vast amounts of information. It looks at Mars, of course, but also the two dinky and weird moons Phobos and Deimos. For example, a little while back it took this phenomenal shot of Phobos over the limb of Mars:

[Click to greatly barsoominate.]

That’s fantastic! Note how dark Phobos appears; it really is much less reflective than Mars. Its origin is unclear, but a popular idea is that it’s an asteroid Mars captured long ago. I’ve never been comfortable with this idea, since capturing an object is extremely difficult. An asteroid moving past a planet will just fly on by unless it is slowed considerably, and there aren’t many ways to do that. If it passes extremely close, the atmosphere of the planet might slow it sufficiently, but that results in a highly elliptical orbit that’s unlikely to last very long. Perhaps Phobos was a binary asteroid, and one of the two components absorbed the extra energy and was ejected, while the other settled into orbit and became Phobos. Maybe it got its start in some other way entirely.

We’ll hopefully learn more when the Russian probe (and lander with sample return!) Phobos-Grunt launches later this year. In the meantime, Mars Express is in an orbit that periodically brings it close to Phobos several times, and we’re entering a new season of passes right now. In fact, it just had a close encounter with Phobos, and word has it the flyby was a success! That means we’ll soon be getting more even interesting and beautiful images of this enigmatic little moon, so keep your eyes open for them.


Related posts:

More incredible Phobos imagery
Phobos: closeup of fear
Deimos!
The shadow of a moon goes passing by


CATEGORIZED UNDER: Astronomy, Pretty pictures

Comments (36)

  1. So much cool science! :D

    “a popular idea is that it’s an asteroid Mars captured long ago. I’ve never been comfortable with this idea, since capturing an object is extremely difficult.”

    Well, given billions of years, why not? It’s difficult to shoot a hole in one, or win a lottery ticket, or a bunch of other really small probability occurences, yet they do happen, with some frequency even. ;)

    That said, I am sure that eventually we’ll find out that something totally unthought of or unexpected is what really happened.

  2. Messier Tidy Upper

    barsoominate

    Ah, your best neologism yet! LOL. :-)

    Although I’d also suggest that en-Malacandrate might work almost as well. ;-)

    Excellent photo, excellent news & it reminds me of an article in New Scientist magazine (if memory serves, ’twas a fair while ago now – last year or the year before, many months ago) suggesting the Martian moons may be our first landing sites outside the Earth-moon system – landing and exploring there before we get to Mars in person as opposed to in-robot.

    Personally, I’d bet on us visiting a Near-Earth Asteroid myself, human space exploration~wise, but anyhow. ;-)

  3. Messier Tidy Upper

    See :

    http://en.wikipedia.org/wiki/The_Space_Trilogy

    For why “Malacandrinate” might work – although if you know why “Barsoom” best applies you can probably already guess. ;-)

    Incidentally, my fave SF work Mars~wise is Kim Stanley Robinson’s eponymous trilogy :

    http://en.wikipedia.org/wiki/Mars_trilogy

    although Ben Bova’s Mars :

    http://en.wikipedia.org/wiki/Return_to_Mars

    is a close second. :-)

    (What? The only have a dedicated page for the sequel on wikipedia? Seems so. )

    The Greg Bear novel ‘Moving Mars’ gets my bronze medal podium place btw.

    Still those lack a certain something when it comes to melodious Mars monikers. ;-)

  4. MadScientist

    Don’t you mean ‘Wabbit’ ?

    I hope the Russian mission succeeds (remember the Curse of the Russian Landers?) Could they knock the moons out of orbit?

  5. Messier Tidy Upper

    @ ^ MadScientist : Only if they’ve got enough “grunt!” ;-)

    Hmm .. surely that euphemism for power /strength isn’t just an Aussie thing.

  6. Unaspammer

    What is “Rab Phobos season”? If you’re going to backspace out the word, you need to backspace out the whole word.

  7. Why does the Martian surface look so wavy? This isn’t the first photo from Martian orbit that’s had that wavy effect that I’ve seen, but the particular pattern looks more like a weird camera artifact than an actual surface feature of the red planet.

  8. QuietDesperation

    That’s no moo- oh, wait, yes it is.

  9. Messier Tidy Upper

    @6. Unaspammer :

    I’m seeing the whole “rabbit” word here.

    I must admit I’m not sure what the whole deal is with the :

    It’s rabbit^h^h^h Phobos season!

    title is or what you’re meaning about backspacing there?

  10. Messier Tidy Upper

    @8. QuietDesperation : That’s no moo- oh, wait, yes it is.

    Unless you say its really just an asteroid? ;-)

    Albeit one that got captured into orbit around a planet as quite a few do although usually around more massive gas giant worlds rather than ones as small as Mars.

  11. Trebuchet

    @6: I think that’s just the effect of the highly oblique camera angle emphasizing the natural undulations of the surface.

  12. Messier Tidy Upper:

    I must admit I’m not sure what the whole deal is with the :

    It’s rabbit^h^h^h Phobos season!

    title is or what you’re meaning about backspacing there?

    Perhaps you’re not familiar with Bugs Bunny cartoons? (Bugs and Daffy try telling Elmer Fudd to shoot the other one — It’s duck season. It’s rabbit season. It’s duck season. Etc.)

    The “^h” backspacing thing is a common way of saying something online while pretending not to say it. (Such as BA’s oft-used “hive overmind” references.)

    So, this was his way of making a reference to Bugs/Daffy, whch gives the real title “It’s Phobos Season” a meaningful point of reference.)

    The problem, as pointed out by Unaspammer, is that he only used three “backspaces”, leaving “rab” intact.

    Another common form is “^W”, which is used to “backspace” an entire word, such as “I was told by that idiot upstairs^W^W^W the CEO to do [something]”.

  13. Gary Ansorge

    Phobos looks like a big chunk of coal,,,hmmm,,,maybe Santa was mad at Mars?

    One of the best pics I’ve ever seen of Phobos against Mars.

    Gary 7

  14. angelo

    apparently, the recent finding of hydrated silicates on Phobos, together with its (very) low density, added significant weight to the “impact then re-accretion” hypothesis (e.g. http://www.universetoday.com/74073/)

  15. Keith Bowden

    QuietDesperation:
    That’s no moo- oh, wait, yes it is.

    Then again…

    I’m not being snarky (I’m fine with the Pluto reclassification, though it still “feels” odd), but shouldn’t we differentiate between larger spherical moons and smaller irregularly-shaped satellites?

  16. Kostas

    That post kinda made my day. I am doing my thesis on an imaging spectrometer on board Mars Express and i was really frustrated at some point and realized that i am getting lost in the technical details and that i am missing the larger picture. This post helped me remember why i am doing this and why those technical details really matter.

    By the way why are the cameras getting all the attention? Imaging spectrometers are like cameras but also record the spectrum at the same time. How cool is that?!

  17. andy

    Last I heard, the theory that the moons of Mars were produced from material blasted off the planet in an impact (a bit like the explanation for the formation of our own moon, but with a less impressive collision) was gaining popularity.

  18. jearley

    Speaking of Barsoom, you all did know that a major money/effects/ etc. Movie is being made of John Carter of Mars. right? I really hope that they do not screw it up.

  19. QuietDesperation

    Speaking of Barsoom, you all did know that a major money/effects/ etc. Movie is being made of John Carter of Mars. right?

    Yes.

    I really hope that they do not screw it up.

    Ha ha ha ha! Dream on. :-P

  20. CB

    @ 15:
    I’m not being snarky (I’m fine with the Pluto reclassification, though it still “feels” odd), but shouldn’t we differentiate between larger spherical moons and smaller irregularly-shaped satellites?

    Sounds good to me. How about we name the ones in hydrostatic equilibrium after the largest such example, and call them “Titanoids”.

  21. Joseph G

    Is it just me, or does the surface of Mars in that pic look like a texture-map with bilinear filtering applied (Computer gamers will know what I mean)?
    Maybe it’s just a combination of atmospheric effects and the extreme surface angle?
    Or maybe Richard Hoagland is right, and NASA is sending us fake images of craters photoshopped in to cover the enormous Martian cities :P

  22. Joseph G

    Phobos is one of my favored locations to visit, if they ever manage to get interplanetary spacecraft down to my price range :D It’s an intriguing place, and I share a name with the guy who discovered it :)
    If anyone here has heard of the Orbiter simulator, try exploring Phobos – the sim really gives you an idea of how big (by human standards) and how tiny (by astronomical standards) the thing is. There’s even a mod that has a handy little refueling base on the surface of Phobos.
    IIRC, the escape velocity at the surface is something like 40 kph, and trying to land in the sim gives you a good feel for it. I’d love to try hopping around on the surface in a space suit (seems like if you took a good jump you’d very nearly go into orbit).

  23. Joseph G

    @16 Kostas: Very cool, indeed!

  24. Elias

    Phobos looks tiny – there’s no sense of the scale of the craters. I know it’s only 27km across in its longest dimension, but I still wonder whether familiar objects (like a house, for instance) could be seen on the surface from the distance this photo was taken.

  25. Matt B.

    I’m glad to hear Phil’s as skeptical of the asteroid capture hypothesis as I am. It just doesn’t make sense in a two-body problem.

  26. “Phobos looks tiny – there’s no sense of the scale of the craters. I know it’s only 27km across in its longest dimension, but I still wonder whether familiar objects (like a house, for instance) could be seen on the surface from the distance this photo was taken.”

    I was wondering the same thing. Wikipedia says Phobos has a mean radius of 11.1 km , or 6.9 miles. Just by eyeballing the photo, I was trying to imagine something the size of the Sears Tower (excuse me, “Willis” Tower) on the surface. It’s 442m tall, so we’re talking about something like 4% of Phobos’ average radius. On my monitor, the Phobos in the barsoomed pic is about 200 pixels across, giving a radius of about 100px.

    So if one of the world’s tallest skyscrapers were sitting atop Phobos in this picture, you could see it, as a 4-pixel tall speck.

  27. CB

    @22 John G
    Phobos is one of my favored locations to visit, if they ever manage to get interplanetary spacecraft down to my price range :D It’s an intriguing place, and I share a name with the guy who discovered it :)

    I’ve visited Phobos before, and let me tell you, you do NOT want to visit. The place is absolutely stuffed with Hellspawn, and the humans they’ve turned into gun-toting zombies. That’s right: On Phobos, the zombies shoot back. And they’re the pleasant part.

    I give it 1 star.

  28. Meskine

    Those Russians sure can name a probe.

  29. Joseph G

    @#27: Don’t forget the boring architecture – all one-story construction! And no ramps whatsoever – Phobos apparently isn’t wheelchair-accessible.
    Not to mention the explosive barrels laying around everywhere. That place is a lawsuit just waiting to happen.

    @#28 Meskine: I’m eagerly awaiting their next probe, the Europa-Gurgle.

  30. Sam H

    @Jeff Edsel:
    “So if one of the world’s tallest skyscrapers were sitting atop Phobos in this picture, you could see it, as a 4-pixel tall speck.”

    Holy mother dang. :o

    This pic is AMAZING :D!! Actually, it’s amazing to the point of being unbelievable. Mars is so close and flat that for a minute I thought this was fake. Is an angle like that for observing Phobos (ultra-high magnification or not) even possible?
    It isn’t just the universe that never ceases to amaze – it’s the techniques of our own imaging scientists!!
    (insert Reptillian conspiracy here) ;)

  31. T-storm

    I took a phobos grunt once.

  32. Grant

    @ Meng Bomin: Yeah I noticed that too. (the wavy horizon thing) It looks like a scanner artifact if you move the piece of paper or something while it’s scanning. Since the probe is pointing at Phobos, maybe mars is moving in the background, and the camera onboard doesn’t take images in a single snapshot but has an internal scanning device to capture them?

    @ The Bad Astronomer: I never liked the “asteroid capture” theory either. It’s my understanding that, neglecting massive tidal forces or atmospheric drag or a collision, two bodies approaching each other that aren’t initially in closed orbits around each other are going to end up not in closed orbits around each other. You’d have to have a third body to “slingshot” around the asteroid and give it a push at precisely the right time to get it to stay in orbit. The odds of that happening always seemed…[puts on sunglasses] astronomical to me.

  33. Yojimbo
  34. Joseph G

    Fun factoid: Phobos orbits Mars more then once per Martian day. This means that the same tidal forces that cause our Moon to recede from the Earth are causing Phobos to orbit closer and closer to Mars. Within the next 7 to 9 million years, it’s expected to either break up into a ring (likely) or hit Mars itself (it’d need to be very solid and highly metallic to do this).
    Considering the length of time the system’s probably been around, a few million years is nothing. We got here just in time to catch Phobos towards the end of its life :)

  35. Joseph G

    @#32 Grant: That makes a lot of sense, actually. Phobos is extremely dark in color, so to get a good image of it, I’ll bet the exposure time was (relatively) high. High enough for orbital motion to show, anyway.

    As far as the origin of the system, I thought I read somewhere that Mars’ lack of magnetic field allows solar wind to erode away the atmosphere, and that the Martian atmosphere may have once been much more substantial. In any case, a thick atmosphere would make the aerobraking capture scenario (slightly) more plausible, I’d think.

  36. Messier Tidy Upper

    @ ^ Joseph G : Yup. That theory sounds very likely right to me. :-)

    There is good reason to think Mars certainly had a thicker, denser, warmer atmosphere in the past – and an ocean or sea in the northern Vastitas Borealis region and possibly elsewhere too. The Mars rovers seem to have shown liquid water used to exist in some regions & plausibly microscopic life too.

    @12. Ken B : Thanks for that explanation. It makes sense now. :-)

    @15. Keith Bowden Says:

    QuietDesperation: “That’s no moo- oh, wait, yes it is.
    Then again…”
    I’m not being snarky but shouldn’t we differentiate between larger spherical moons and smaller irregularly-shaped satellites?

    I think so too & would agree with (#20.) CB – although I’d suggest the term “moons” for the larger rounded ones & “moonlets” for the smaller irregular ones.

    For instance, Pluto would then boast one moon – Charon – & two moonlets – Nyx and Hydra. Mars would have no moons but just two moonlets, etc ..

    (I’m fine with the Pluto reclassification, though it still “feels” odd)

    I’m not. I think it was a terrible decision for a number of logical reasons. :-(

    But that’s another story again ..

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