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Space Science

Phobos and Deimos Once a Single Moon? 60

Posted by michael from the family-ties dept.
blamanj writes "Phobos (fear) and Diemos (panic), the twin moons of Mars have caused astronomers grief for years, as conventional hypotheses about the moons either violate physical laws or have difficulty accounting for their observed orbits. Now a new hypothesis conjectures that they were once a single moon, that broke apart in an ancient catastrophe."
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Phobos and Deimos Once a Single Moon? More

Phobos and Deimos Once a Single Moon?

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  • FUD (Score:5, Funny)

    by limekiller4 ( 451497 ) on Tuesday July 29, 2003 @06:19PM (#6565615) Homepage
    Great. Now we just need to find moons Metus (fear), Ambiguitas (uncertainty) and Dubium (doubt) and convince Gates to purchase them...
    • Haven't those three long since crashed into the Earth?

    • Re:FUD (Score:1, Informative)

      by Anonymous Coward
      Metus, Ambiguitas, and Dubium are latin; whereas Phobos and Deimos are Greek... If my math is correct, of course.

      • Re:FUD (Score:3, Informative)

        by Antisthenes ( 579582 )
        They are, and it goes without saying that Greek is the superior tongue. ;-) Uncertainty would be amphisbetesis, "dispute, controversy" (those e's are eta's, by the way, not epsilon's) and doubt would be apistia, "unbelief, distrust".

        S.C. Woodhouse, English-Greek Dictionary [uchicago.edu]
        Henry George Liddell, Robert Scott, A Greek-English Lexicon [uni-bremen.de]

  • Doom? (Score:3, Funny)

    by sirmikester ( 634831 ) on Tuesday July 29, 2003 @06:34PM (#6565744) Homepage Journal
    Maybe the catastrophe was related to the demon's gate that was forming... and was later reopened in the Doom games... think about it.
  • Awesome! It's about time we set up a base somewhere we don't have to wait for months to get results from launches. But is that any cheaper than maintaining the supply chain to a base (food, air, parts)? Logistics, anyone?

  • S. Fred Singer INFO (Score:4, Interesting)

    by MonkeyBoyo ( 630427 ) on Tuesday July 29, 2003 @07:25PM (#6566208)
    I don't know how "new" this theory is. Here is some info on S. Fred Singer [cosmos-club.org].

  • Doubtful (Score:5, Interesting)

    by CheshireCatCO ( 185193 ) on Tuesday July 29, 2003 @09:47PM (#6567209) Homepage
    Right, there's a lot here that makes me dubious of the claim. First off, I should point out that I've worked on the capture problem for Mars's moons. (The results haven't been published, although the did land a grant.)

    First off, why is synchronous orbit a hint as to their breakup? There's no reason that synchronous orbit is preferred, either as a capture point or as a point for breakup. In fact, synchronous orbit is an unstable equilibrium: a slight perturbation drives everything away from it. (Which is why Phobos is heading inward and Deimos outward.)

    Also, he needs to explain why a larger moon orbited there happily (without perturbation!) for billions of years before breaking apart. In the very least, we're witnessing Mars's moons at a very unusal time, and such coincidence make me (and most astronomers) nervous.

    Also, Phobos has drifted inward since any such breakup. Why isn't it breaking up more? Unless there's some internal strength (in which case, why did it break up then?), it should.

    To be honest, I sort of question his background for this. Besides the fact that he's not an astronomer, he wants to put a base on Deimos? The surface gravity on those moons is virtually non-existant. (For Deimos, being smaller, it's under 1 cm/sec^2, I believe.) No one could even walk around properly. (Although, if he hollowed it out and made a colony ship out of it, we could launch it to Tau Ceti... But it might encounter some hostile, three-eyed aliens.*)

    I'd be happy to hear him explain his idea to a group of dynamicists. Hell, I'll volunteer. But I'm very skeptical for now.

    (* Kudos to anyone who catches *that* reference.)

    • Re:Doubtful (Score:3, Interesting)

      by Tablizer ( 95088 )
      Which is why Phobos is heading inward and Deimos outward.

      I am curious as to why they are drifting. Anybody have the scoop?

      • Re:Doubtful (Score:5, Interesting)

        by CheshireCatCO ( 185193 ) on Tuesday July 29, 2003 @11:42PM (#6567879) Homepage
        Glad you asked!

        Let's start with moons outside of synchronous orbit. These moons raise a tidal bulge on their planet. (The one on Earth is most apparent in the oceans. Or, rather, at their edges. But there's a bulge in the rock, too.) Now, the planet is spinning and it isn't a perfect fluid. So it will tend to carry the bulge forward with it, before the bulge can move back to under the moon where it wants to be. A balance is struck between these two competing forces where the bulge rides somewhere ahead of the moon.

        The moon, then, feels a tug forward in its orbit. This tends to give it angular momentum, so that it drifts outward. (Angular momentum increases as you go out from the central object.) The planet, meanwhile, is being pulled backward so that its spin slows down. (As it must, to conserve angular momentum in the system.) This is why Earth's day in lengthening and why the Moon has drifted about 60 Earth radii from where it formed over the past 4.5 billion years.

        What happens of the moon is *inside* synchronous orbit? The opposite happens: the moon moves ahead of the bulge and gets pulled back. So it drifts in.

        I'll leave it as an exercise to the reader to work out what retrograde (backward orbiting) moons do. Triton is an example, by the way.

        • Re:Non-Linear Dynamics (Score:3, Informative)

          by quinkin ( 601839 )
          I agree that that is the situation in a classical two body system.

          Unfortunately, classical physics cannot calculate a three-body system (it can be approximated quite closely by using iterative two-body calculations and restricted three-body techniques etc.).

          The Earth/Moon orbit, is not periodic but is in fact quasi-periodic (so it has an near periodic cycle - or time to return "near" to origin).

          I'll leave calculation of the three body integral as a readers exercise (bad physicist joke).

          Q.

          • Er, what's your point? The moons are behaving as predicted by the theory, just like ours is. There's obviously some error in it, but there always is. (There's error in our orbital calculations for the Earth, another thing we can't actually integrate exactly. Do you not believe that we know pretty well where Earth will be in a month?)

        • Re:Doubtful (Score:3, Informative)

          by Alsee ( 515537 )
          Good explanation, thanx. That's sort of been itching at me but I never asked/checked why it works in that direction.

          an exercise to the reader to work out what retrograde (backward orbiting) moons do

          The bulge would lag even more and the moon would spiral in even faster no matter where it is.

          I don't happen to be an expert on Triton, but I would therefore conclude that it is a young moon and started with a much larger orbit.

          -
          • Exactly on the first point.

            Not sure of the timescale on the second point. All of this depends on not just the planet's spin and mass, but also on the mass of the moon (bigger is actually better, as I recall), the moon's distance and the tidal reponse of the planet. Since Neptune's upper layers are pretty fluid, I'm guessing that they don't dissipate much and so Triton doesn't move as fast as the Moon. But I'd need to check up on that. (Earth-Moon face a lot of evolution, more now than is typical, becau
            • I just tried google and a couple of sources say something like the following:

              Triton could not have condensed from the primordial Solar Nebula in this configuration; it must have formed elsewhere (perhaps in the Kuiper Belt?) and later been captured by Neptune

              So at least in some sense it is "young" in that it didn't start there, it was later captured. I haven't seen any further discussion of the age, but I didn't look very hard.

              -
              • Yeah, you get that from the fact that it orbits retrograde and its orbit is fairly inclined relative to Neptune's equator. That said, damn if we know how to capture such a huge chuck of ice and rock as Triton. Although it seems easier to do when the planet is very young and has a more extended atmosphere.

    • Re:Doubtful (Score:3, Interesting)

      by WolfWithoutAClause ( 162946 )
      Besides the fact that he's not an astronomer, he wants to put a base on Deimos?

      No, he's right, or in orbit around it. It makes a lot of sense. There's probably ice on Deimos and/or Phobos. If so, that's rocket fuel; the space equivalent of oil. And Deimos is ideally placed for this- it's high up above Mars (but not so far that you can't go down), and close in delta-v terms to the Earth, ideal for sending fuel back to Earth orbit to fuel Mars and Lunar missions. It's also a great source for rock for use fo

      • Re:Doubtful (Score:3, Insightful)

        by CheshireCatCO ( 185193 )
        Walking is generally important, unless you want the astronouts to stay seated all the time. If there were in zero-g, they could float. But there's enough gravity to make that annoying, but not nearly enough to walk. Also, they'd still need to do daily exercises to keep their bones and muscles from atrophying.

        You're making a pretty large leap from "probably water" to "send fuel back to Earth". There probably isn't that much water to start with, given that these guys are a few kilometers across.

        It's not
        • If there were in zero-g, they could float. But there's enough gravity to make that annoying, but not nearly enough to walk.

          Garbage. If the gravity is 1cm/s^2, then that is 1/1,000g. It takes about 14 seconds to fall down from a height of 1m and when you hit the deck, it's like you've fallen 1mm. That's zero-g in my book. No you can't walk- but you don't need to.

          Also, they'd still need to do daily exercises to keep their bones and muscles from atrophying.

          Yup. It would be possible to send a centrifuge th

          • You also have to land the base onto the moon, and then secure it down. Do you know how hard it is to land in that kind of gravity? Really? It took a lot of careful effort to manuver NEAR/Shoemaker around Eros. And they didn't have to contend with a nearby Mars.

            "Do you have any idea how much mass a 'few kilometer' body contains? Clearly not."

            One might have assumed that, in order to calculate the surface gravity, I actually used that number. But that would ruin your attempt to take a swipe at me, would

            • Re:Doubtful (Score:3, Informative)

              by WolfWithoutAClause ( 162946 )
              Do you know how hard it is to land in that kind of gravity?

              Yes. It's trivial.

              It took a lot of careful effort to manuver NEAR/Shoemaker around Eros.

              I wasn't born yesterday. That was because the speed of light made it really difficult to remote control the vehicle at that distance. Stick a man onboard and it's really, really easy.

              Asteroids formed inside the "frost-line" in the protoplanetary disk.

              True, kinda. But so did the Earth. The frost-line doesn't form until the protoplanetary disk gets blown a

              • OK, this is my last post on this, because it's become clear that you really don't know the details.

                First, the speed of light lag was only part of the landing on/orbit around Eros problem. I know, I've spoken with many of the mission scientists. And, no, it isn't trivial. You can't dismiss it that easily.

                In the case of Deimos, is a postive SOB. You'll have to orbit within around 11 km of the average surface if you go retrograde, 5 if you go prograde. Given that you're orbiting a moon that is only 6 km
                • First, the speed of light lag was only part of the landing on/orbit around Eros problem. I know, I've spoken with many of the mission scientists. And, no, it isn't trivial. You can't dismiss it that easily.

                  Yes, you very much can. When the vehicle has enormously more thrust than its weight it becomes just a control issue, and people are very good at control. I'm not belittling the Eros team in any way- it's just that the problem they solved is not the same issue as landing on Deimos or even Eros with a man


    • First off, why is synchronous orbit a hint as to their breakup? There's no reason that synchronous orbit is preferred, either as a capture point or as a point for breakup. I dont think the article suggest it is, in fact I suggest that since
      In fact, synchronous orbit is an unstable equilibrium: a slight perturbation drives everything away from it. (Which is why Phobos is heading inward and Deimos outward.)

      I think this is what he is suggesting, a synchronous orbit is not prefered because it is unstable.
      • Perhaps he is suggesting that, but it's wrong. Angular momentum is transfer to the moon as a body force, not diffrentially. The moon can simultaneously run ahead of the bulge and behind it. In fact, at synchronous orbit, it does neither. It's perfectly aligned. Which is why the Earth-Moon system is heading for that right now. (It won't be stable for Earth, but that's because we feel the effects of the Sun pretty strongly, too. Pluto-Charon are already there, and are fairly happy. But they're really

  • Lol (Score:1, Funny)

    by Anonymous Coward
    Am i the oney one how thourght the wording of this funny

    Origin of the two moons presents a longstanding puzzle to which one researcher proposed the new solution at the, 6th International Conference on Mars, held here last week.

  • Still There? (Score:4, Interesting)

    by Markus Registrada ( 642224 ) on Tuesday July 29, 2003 @11:41PM (#6567872)
    What, is that moon still there? Sometimes it seems like things just go around and around the drain forever.

    Seriously, it's funny how astronomers always think that nobody will touch these rocks that are just sitting there in handy orbits. It's the same with Cruithne, the asteroid that co-orbits earth. They always say it will join Earth again in 600 years (or whenever), and it never seems to cross their minds that we might have found something more useful to do with it by then.

    Deimos will probably be more useful, though, than Phobos, as a counterweight to attach to the end of the big elevator down to the surface. We might have to move Phobos out of the way -- making the elevator shimmy this way and that so that Phobos just misses colliding each time past is asking for trouble.

    • it's funny how astronomers always think that nobody will touch these rocks that are just sitting there in handy orbits.

      Well you see, they spent so much time tweaking their model that (by this point) they don't even want to contemplate having to predict events caused by human intervention.
      =-)

  • Thats no moon... (Score:4, Funny)

    by andersen ( 10283 ) on Wednesday July 30, 2003 @12:42AM (#6568202) Homepage
    Thats no moon... Its a space station.
  • Ok, I don't KNOW, but I am quite certain no animals, bugs, fishes or whatever where harmed when the moon became moons. So why was it a catastrophe?
  • $30 billion is nothing. Cut the military budget by that much. They get something like $350 billion. Or the shuttles. That would be sweet as.

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