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Space Science

New Moon of Jupiter Discovered 152

Posted by CowboyNeal from the heavenly-bodies dept.
xihr writes "Astronomers have discovered a new moon of Jupiter, bringing its known retinue of satellites to a whopping 40. The new moon, designated S/2002 J1, is only 3 km wide, and has a highly inclined and eccentric orbit. Astronomy.com has the story."
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New Moon of Jupiter Discovered More

New Moon of Jupiter Discovered

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  • moon (Score:1, Insightful)

    by Anonymous Coward
    I personally wouldn't think of this as a moon, i'd think it was a part of the jupiters rings

  • Questions (Score:5, Interesting)

    by MattC413 ( 248620 ) <MattC413NO@SPAMhotmail.com> on Saturday December 28, 2002 @10:52AM (#4972166)
    Only 3 km wide? At what point does it go from being a relatively small chunk of rock floating around a planet to being a moon?

    Would it be possible haul enough of a mountain into space orbit to be technically classified as a moon? I mean, man has walked on Earth's moon.. but is he able to make one himself? Or has he already?

    -Matt
    • It'd be funny until it came crashing down into Earth, but it would also give us an excuse to then do sequels to Armageddon and Deep Impact. With Affleck and Elijah Wood so big now, it's worth Hollywood's investment money to launch a mountain into orbit, so that they can them film movies about it.
    • Only 3 km wide? At what point does it go from being a relatively small chunk of rock floating around a planet to being a moon?
      The point where you can't see it from Earth, I suppose. Course, that means that as adaptive optics get better, the criterion gets more all-encompassing.

      Would it be possible haul enough of a mountain into space orbit to be technically classified as a moon?
      Most asteroids are mostly metal (unless you're an astronomer, in which case they're all metal), so the ISS could qualify. If it doesn't, you're out of luck; no-one in their right mind would spend the billions of dollars necessary to get into orbit something can't even support a crew capable of doing anything more than just keeping the damn thing from falling.
      • unless you're an astronomer, in which case they're all metal

        Could you elaborate on this, please?

        • Re:Questions (Score:5, Interesting)

          by Simon Field ( 563434 ) on Saturday December 28, 2002 @12:18PM (#4972402) Homepage


          Astronomers and cosmologists use the term "metal" as a shorthand for anything other than hydrogen and helium.

          • Re:Questions (Score:3, Interesting)

            by Hentai ( 165906 )
            Which is kinda wacky, considering that - chemically - Hydrogen behaves as a 'metal' (in the classical sense) in certain circumstances, and the other nobles (neon, argon, etc.) will NEVER behave as anything other than a noble (well, except xenon, but once you get that much separation from your orbital field and your nucleus, all bets are off.)

            Just goes to show that even scientists can fall into the trap of ambiguous contextual terminology. It'd be nice to go through and create a single, agreed-upon, interdisciplinary scientific language, where when you talk about something, everyone knows what you're saying. (While we're at it, let's set the speed of light to 1 and try and normalize as many fundamental constants as possible.)
            • While we're at it, let's set the speed of light to 1 and try and normalize as many fundamental constants as possible.

              This is already done--sort of--in quantum mechanics. Most problems can be restated in so-called atomic units where the electron charge is -1, Planck's constant (h-bar) is 1, the electron's mass is 1, and the unit length is the Bohr radius (a_nought). The unit of energy becomes the hartree, equal to e^2/a_0, which is 1 in this new system. Anyone who does much in the way of computational chemistry works almost exclusively in these units to get rid of all the messy conversions and constants.

              Unfortunately, in atomic units the speed of light c is equal not to 1 but to the inverse of the fine structure constant alpha. Though this makes c a more manageable 137 (roughly) it's not quite down to one. Besides, these units aren't particularly useful on a human scale.

              Upon further investigation, I should note that some astronomers and cosmologists do set c to be exactly 1. They also make use of such handly length scales as light-seconds. Erm.

              It took decades to gain near-universal acceptance of the metric system, despite its advantages. Indeed, there still exist one or two backward nations that refuse to adopt SI. How do you propose we convince people to accept a system where the posted highway speed limit will be on the order of 0.0000001?

          • Astronomers and cosmologists use the term "metal" as a shorthand for anything other than hydrogen and helium.

            Why am I not surprised?

            Heck, I think physics and chemistry has two opposing views on electron charge flow, and electrical engineering holds that both are true. It's pretty frustrating to deal with this sort of crap.

    • Re:Questions (Score:2, Funny)

      by Anonymous Coward
      If it is made from green cheese, it is a moon. If it is made from rock (or pixels), it is an asteroid.
    • Seriously, it does seem to be a bit silly to call something this small a moon, especially relative to Jupiter, which has several moons worthy of the name. IMO we should set (completely arbitrary, yes) lower limits on what we call both planets and moons:

      1) If it freely orbits the Sun (or some other star, which is now becoming more than an academic distinction), and it's Pluto-size or larger, it's a planet. (To get rid of the "Pluto is not a planet" silliness.) Otherwise it's an asteroid, a comet, a Kuiper belt object, whatever.

      2) If it orbits a planet orbiting the Sun (or some other star, etc.) and it's either a) larger than Phobos or Deimos (whichever is smaller, I forget) or b) larger relative to the planet it orbits than min(Phobos,Deimos) is relative to Mars, then it's a moon. Otherwise, it's a captured asteroid, or a microsatellite, or whatever. And yes, this means Earth only has one moon, and will for some time, until we build a space station larger than min(Phobos,Deimos) -- which will be a while, I gloomily suspect.

      Like I said, this is completely arbitrary, but it has the advantages of both retaining historical classifications and satisfying the original version of Occam's razor. (Don't multiply entities unnecessarily.) There's a lot of stuff floating around the Solar System, and we're finding more all the time. How many damn planets and moons do we really need? ;)

      • Re:Questions (Score:5, Informative)

        by Hentai ( 165906 ) on Saturday December 28, 2002 @12:48PM (#4972513) Homepage Journal
        Actually, even better:

        If it freely orbits a star, is IN THAT STAR'S PLANE OF THE ECLIPTIC, it's a planet (note: this knocks Pluto off the list). You still need some arbitrary limits here, though: I'd say as long as the normalized dot product of the orbit's normal vector with the plane of the ecliptic is within four sigma, you can call it a planet (note - don't take the absolute value - if it's going the wrong way, it's not a planet). Interestingly enough, this places most of the asteroids in 'planet' status.

        That pretty much limits planets to objects which were clearly formed from the accretion disk of the star, as opposed to 'leftover junk' (which something like Pluto most assuredly is). Of course, this also means that a planet can get knocked out of its original orbit, and lose its 'planet' status, but this is also an acceptable side-effect if you want definitional consistency.

        For 'moon', any body which orbits a planet within two sigma of ITS plane of ecliptic should be considered a 'moon'. Here we need a good definition of 'orbit' - if, at any time, an object's orbit brings it *away* from the center of mass of its solar system, and towards its planetary primary, it's in orbit around that planetary primary, and not its star. This means, incidentally, that the Earth's Moon is not a moon - it's another planet that happens to co-orbit the sun within the same boundry space as the Earth, and the two planets perturb each other's orbits.

        Any body which does not fall under this criteria is a 'satellite' of its primary, but not a 'planet' or 'moon'.

        While this definition leads to a few counter-intuitive situations (or at least, counter-traditional), that's inevitable when formalizing terminology. People use words too loosely to expect all possible cases to fit the 'traditional' nomelcatures, so when formalizing, you sometimes have to accept a few deviances (for example, if we were to normalize biological taxonomy, dogs, wolves, coyotes, and jackals would all be the same species - since they're genetically capable of interreproducing. It's only weight of tradition that keeps them seperate, a very unscientific concept.)

        • Re:Questions (Score:2, Insightful)

          by podperson ( 592944 )
          Here we need a good definition of 'orbit' - if, at any time, an object's orbit brings it *away* from the center of mass of its solar system, and towards its planetary primary, it's in orbit around that planetary primary, and not its star. This means, incidentally, that the Earth's Moon is not a moon - it's another planet that happens to co-orbit the sun within the same boundry space as the Earth, and the two planets perturb each other's orbits.

          This seems to be a bad and ambiguous definition and an erroneous interpretation of that definition.

          1) It's circular. You definite orbit in terms of orbit.

          2) The Earth is, at some point in its orbit, moving closer to the Moon and away from the sun, ergo it is the Moon's moon. And vice versa.

          3) The Earth is, at some point in its orbit, moving closer to Neptune and away from the Sun, ergo it is Neptune's moon.

          Surely the simple criterion is along the lines:

          1) if we can see A moving around B and C, and we were to remove the influence of C, and then A continues around B, A is orbiting B -- if they would just fly off to infinity (or otherwise approximate a hyperbolic orbit) then A is not orbiting B.

          2) if A and B satisfy condition 1, then we say A orbits B if A is (some degree of our choosing) less massive than B. If they are within (some degree of our choosing) we say they orbit each other.
          • Note that under this definition, the Moon is orbiting the Earth. The Moon is also orbiting the Sun. The Earth is orbiting the Sun.

            We can then say that a body is a "moon" if it is (closely) orbiting a larger body which may itself be orbiting a star. (I use the word "closely" since we might well find that the moon is also orbiting Jupiter, for example, under this definition, and this is a perfectly reasonable finding.)
          • Thank you. That's what I MEANT to say, but I had a major semantic subsystem glitch about halfway through. Sorry about the obviously bogus definition of 'orbit' I posited.

        • If it freely orbits a star, is IN THAT STAR'S PLANE OF THE ECLIPTIC, it's a planet (note: this knocks Pluto off the list).

          I disagree, mostly because I think that trying to put such labels on things is always going to end up in ambiguities. The reason we call these things planets at all is because ancient observers saw them wandering through the sky. The reason satellites are often called moons is that Moon was the proper noun previously used to name the Earth's most obvious natural satellite. When more satellites were found around Jupiter and other planets, people called them moons. (I think the moon thing is true, but I haven't confirmed it.)

          Furthermore, your definition is based on ruling out bodies that "weren't formed as part of the star's disc", but it hasn't even been established that stars (and planets) formed in such a way. What's so bad about ambiguities?

          Humans are naturally experienced and equipped to deal with ambiguities. It's one of the things people excel at that machines don't. Why does it need to be categorised? Computers normally need categorisation for calculations, but computers can do what they need to do just by seeing them as blobs orbiting other blobs. Arbitrary labels are irrelevant. That's my point of view, anyway.

        • The IAU (International Astronomical Union) is the organization in charge of designation the class of objects. At present, and as it should be, there are no objective classifications for names like planet, asteroid, comet, etc. These classification systems, after all, are artificial ones imposed by us on nature; there's no reason to think that there's anything special when you call an object a planet vs. an asteroid.

          In the real world, we're imposing an arbitrary classification on a system involving many dimensional characteristics (distance from primary, inclination, eccentricity, size, and on and on). It's not surprising that the names that we got from antiquity aren't very good. After all, even the words themselves hint that there's nothing special here: planet comes from the Greek for "wanderer," and asteroid just means "star-like."

          Any objectivized definition will be arbitrary (where do you define the cutoffs), and will probably include things we don't want to include. The classification system the above poster gave, for instance:

          If it freely orbits a star, is IN THAT STAR'S PLANE OF THE ECLIPTIC, it's a planet (note: this knocks Pluto off the list).

          Mercury's orbit is actually fairly inlined, and Mars' is rather eccentric; do these then not qualify as planets? Furthermore, there are plenty of main belt asteroids that would then qualify as planets, which is almost certainly not what the original poster wanted.

          The bottom line is that for astronomers to do their jobs, they don't need any reformation of current classification systems. It doesn't matter what you call the bodies in question; whether you call Pluto a planet, an asteroid, or a Kuiperoid doesn't change anything about its inherent nature. It's worth pointing out that pioneering such reclassifications is restricted almost entirely to amateurs, for the simple fact that the professionals don't care.

          • The bottom line is that for astronomers to do their jobs, they don't need any reformation of current classification systems. It doesn't matter what you call the bodies in question; whether you call Pluto a planet, an asteroid, or a Kuiperoid doesn't change anything about its inherent nature. It's worth pointing out that pioneering such reclassifications is restricted almost entirely to amateurs, for the simple fact that the professionals don't care.

            You must be new to the greatest of all scientific strivings: funding.
    • Seems to me that the headline "Jupiter Adds Another to Its Ranks" isn't quite right. How about "Humans Discover 40th Jovian Moon, Take Credit For Putting It There."

      Interestingly, a whole stack of these moons were discovered around 2000 when astronomers decided to search existing photographic plates for them, then went looking for more. I remembered Jupiter have about 12. Read about it here. [arizona.edu] (An intereting solar system site in general.)

      As for moon v. satellite, a moon is simply a natural satellite. Some purists say that only the Earth has a Moon (capitalized) whereas other planets such as Jupiter have natural satellites. As mentioned in the link above, "captured asteroid" is another candidate for these irregular-orbit chunks. Our Moon, meanwhile, is very unusual in the Solar System for its great size relative to its planet -- about 25% IIRC. There are bigger moons elsewhere, but the strength the gravitational Earth-Moon attraction has many dramatic effects. (I've also read that the Moon is more greatly attracted by the Sun than the Earth, thus it orbits the Sun. Please don't ask me to explain or defend, but it sounded plausible [edjohnston.com]...)

      BTW -- someone suggested non-moons are distinguished by being mostly metal (e.g., Landsat) -- well, many asteroids are mostly free metal, too (Fe, Co, Pt, and so on). If you want to split hairs, most rock is made of metallic compounds (Si, Fe, etc.).
      • ... Our Moon, meanwhile, is very unusual in the Solar System for its great size relative to its planet -- about 25% IIRC...

        The moon's diameter is about 25% of the Earth's diameter, but it is the relative difference in diameter that counts for Gravity. The moon is a bit more than 1% of the Earth's mass -- partly because the moon is less dense than the Earth, but mainly because the volume goes up with the cube of the dimensions.

        Pluto and its satellite Charon are also relatively close in size.

        Earlier in this thread someone suggested rules, like the self-referential rule that planets had to be Pluto sized or larger. When I was a kid Pluto was described as being larger than Mercury. So even Pluto isn't Pluto sized.

        • Yeah, Pluto is the "bastard planet," its origins unclear. It could be a former satellite of Neptune.

          Have you heard the suggestion that the Moon really orbits the Sun, and to a lesser extent interacts with Earth? The idea is that the Moon's size plus its slow speed around Earth relative to Earth's speed around the Sun (so there is no retrograde motion) result in the Moon always "falling" towards the Sun. I don't have the math and physics background to evaluate this myself, and was of course startled to read it. read this [edjohnston.com]
    • Technically, "Moon" is the proper name for Earth's major satellite. In common usage though, a moon is any natural satellite of a planet. I have been unable to find specific requirements as to size of satellite, eccentricity of orbit, stability of orbit, etc. which would cause random bits of debris, such as those making up Saturn's rings, to be classified as moons or not.

      My personal criteria would require uniqueness and stability. That is, tiny rocks in a ring are not unique, whereas a single (or two, or 40) orbiting body deserves special recognition. Also, the orbit must be stable. That is, an asteroid captured by a planet's gravity in an orbit that will smash it into something in 200 years is not a moon. It is a pet.
      • As for an offician name for Earth's companion, how about Luna? That's what I thought it was to a number of scientists.
      • Technically, "Moon" is the proper name for Earth's major satellite.
        Technically, I think the proper name for Earths Moon is Luna, but has generally become known as The Moon. Just like The Sun. There are trillions of stars out there, and if you want to get picky and clasify only stars with planets orbiting them as suns, then there are still probably millions of suns out there, but ours is still The Sun, not Sol, as it should be IMO.
    • Would it be possible haul enough of a mountain into space orbit to be technically classified as a moon?

      When will we have the technology to make that a serious question? Not this century, at the rate we're going.

      For what it's worth, international law is that you can't create or expand a country by building an island. If the island isn't naturally above water at high tide, it doesn't count. One of Japan's boundaries depends on a tiny island a few meters across, and to keep it from wearing away, which would cost Japan fishing rights, a breakwater has been built around it.

  • I think we should steal it. (Score:5, Funny)

    by drfishy ( 634081 ) on Saturday December 28, 2002 @10:52AM (#4972169)
    Lets take that moon into earth orbit, it could be fun.

  • Would be fun to live on jupiter.... (Score:1, Funny)

    by Anonymous Coward
    Just imaging... 40 differant solar eclipses a year!!!

  • By Jove!!! (Score:5, Funny)

    by digitalsushi ( 137809 ) <slashdot@digitalsushi.com> on Saturday December 28, 2002 @10:55AM (#4972174) Journal

    By Jove, another moon!

    runs away quickly

  • Old Joke... (Score:5, Funny)

    by Cyno01 ( 573917 ) <Cyno01@hotmail.com> on Saturday December 28, 2002 @10:56AM (#4972180) Homepage
    Thats no moon, its a space station!
  • Its a monolith. Where's HAL when you need him.

  • Stupid name... (Score:5, Informative)

    by PontifexPrimus ( 576159 ) on Saturday December 28, 2002 @11:04AM (#4972201)
    To quote from A. O. Prickard (tr.), "The `Mundus Jovialis' of Simon Marius," The Observatory 39(1916):
    Jupiter is much blamed by the poets on account of his irregular loves. Three maidens are especially mentioned as having been clandestinely courted by Jupiter with success. Io, daughter of the River, Inachus, Callisto of Lycaon, Europa of Agenor. Then there was Ganymede, the handsome son of King Tros, whom Jupiter, having taken the form of an eagle, transported to heaven on his back, as poets fabulously tell . . . . I think, therefore, that I shall not have done amiss if the First is called by me Io, the Second Europa, the Third, on account of its majesty of light, Ganymede, the Fourth Callisto . . . . This fancy, and the particular names given, were suggested to me by Kepler, Imperial Astronomer, when we met at Ratisbon fair in October 1613. So if, as a jest, and in memory of our friendship then begun, I hail him as joint father of these four stars, again I shall not be doing wrong.
    "S/2002 J1"... How romantic, how evocative!
    • Time to start a petition.

      We the undersigned desire "S/2002 J1", Jupiters 40th moon to be renamed "CowboyNeal".
      • Hell yeah.. I was about to post that it should be named "Shayne" (after me).... But CowboyNeal.... What a damn funny way to preserver this little zone in history...

        As much as you meant it as a joke.. It's really a damn fine suggestion.

        "Cowboyneal" the 3k wide geek moon. Bet it's full of wookies.

  • Finally! (Score:3, Funny)

    by Lu Xun ( 615093 ) on Saturday December 28, 2002 @11:18AM (#4972236)
    Does it have tiny volcanos that have to be cleaned every day with a chimney broom? Now we know where that little boy from the stars returns to at the end of every episode!

  • Cool money making scheme (Score:5, Funny)

    by div_2n ( 525075 ) on Saturday December 28, 2002 @11:18AM (#4972237)
    I think space agencies should auction off on e-bay the right to name new celestial bodies. Why not? Everything else is for auction. Could be fun.

    "Class, this is a picture of YourMomNaked as it completes its orbit cycle."

  • Is Cowboy Neal wide enough to count as a moon? (Score:4, Funny)

    by YellowSnow ( 569705 ) on Saturday December 28, 2002 @11:24AM (#4972251)
    Readers have discovered a new post on the linux desktop, bringing its known retinue of dupes to a whopping 40. The new post, designated S/2002 J1, is only 3 k long, and has a highly inclined and eccentric style. Slashdot.org has the story. Again!

  • Moons. (Score:3, Interesting)

    by mraymer ( 516227 ) <mraymer@@@centurytel...net> on Saturday December 28, 2002 @11:28AM (#4972264) Homepage Journal
    Someone else mentioned it seemed a little small to be called a moon. I don't really think there's any size cut off with moons, or planets for that matter. How many of you really think, say, Pluto should really be called a planet? Its moon is roughly the same size as Pluto it self, IRRC. ;)

    That aside, I wonder when the folks working on Celestia [shatters.net] will release an update to display the new moon in the space similator.

    • Re:Moons. (Score:3, Interesting)

      by lvdrproject ( 626577 )
      Actually, yes, Charon is roughly the same size as Pluto. This, along with Charon's orbit, has led many (including myself) to consider Pluto and Charon as a dual-planet system (i.e. they are both planets, orbiting around each other). Meanwhile, there are some that insist that neither is a planet. Astronomy is a tricky business, it seems.
    • The whole thing is rather subjective really. Like when does a boat become a ship?

      The answer in both cases is somewhat similar. A ship is a vessel large enough to carry a boat. Not very enlightening actually, if you insist on rigid taxonomy for every little object in existence. After all, a 22' sailboat can carry an 8' tender on deck, and yet remains merely a boat, not a ship.

      The basic standard for being a planet is large enough to have a moon. Uh huh. Cue the self referencial infinate loop here.

      Although Pluto meets, barely, this standard, quietly in the backrooms it isn't even really considered a planet these days. If we knew as much about it in the 30's it probably never would have been classified as a planet in the first place. "Planet" is also largely considered to only apply to those major bodies that were formed as such with the solar system. Circumstancial evidenced suggests that Pluto started "life" as a moon of Neptune that "got away," possibly knocked out of orbit by a comet.

      That would mean Pluto is a planet that's *also* a moom, although without being a planetary satellite. It's a weird dude, dude.

      The only rule for being considered a moon is being "big enough" to be so classified. Uh huh. Cue thumb up nose routine here.

      The rule of, ummmmmmmmm, thumb, is if you can walk around on it it's a moon. Unless it isn't rocky, we're prejudiced against ice balls. Or maybe if it's discovered on Tuesday. Who knows?

      Of course most of these small moons of the gas giants wouldn't even come close to meeting the formed naturally in the system test. They're pretty much space junk that's ended up stuck in the planet's gravitational field as they wandered by. Captured asteroids. Cue video game joke here.

      Of course if you could literally anthropomorphise a bit of space rock and ask it what it was ( which I don't recommend because they hate that) it would almost certainly say, "Yahwe, now bugger off." It is what it is, and that's all that it is.

      This urge to rigidly classify everything is a human failing. The rocks themselves couldn't care less.

      KFG

      • "This urge to rigidly classify everything is a human failing."
        Why do you classify it as a failing, and with such a sweeping generality no less? Now that you've classified it, have you failed in some way?

        Believe it or not, that's a serious question. Who can explain why classification is so often said to be a failing?

        • It can, and does, bring a considerable amount of understanding when used properly and its limits are well understood by the practitioner.

          The insistence on, and rigid dogmatic application of, certain kinds of classification is the failing.

          Like believing any output made by a computer because a computer made it.

          In this particular case trying to decide whether this object is a moon or not based on its size is a *purely* subjective decision by its very nature. Pretending it isn't would be a failing.

          Another related failing is saying something like, "The theory of relativity forbids. . . ," which is technically true. The theory may well forbid the phenomenon in question, but the theory is a *model* of reality, not reality itself. It is *always* very important to maintain this awareness explicitly or one may easily be led into error, or away from a Nobel Prize.

          Reality just *is,* irrespective of any theory that seeks to model it.

          This does not mean that modeling it is an error, but any model may contain some degree of error and thus rigidly adhering to the model is an error.

          KFG

  • Just Another Captured Asteroid (Score:5, Informative)

    by mbone ( 558574 ) on Saturday December 28, 2002 @11:43AM (#4972307)
    Like all of the newly discovered moons, this little bit of rock is just another captured asteroid - its retrograde (backwards) orbit is a dead giveaway. Simulations show that most of the captured moons will eventually wander back to the asteroid belt - so this is the solar system equivalent of a one night stand.

    BTW, the rings of Jupiter are close to the planet - this new moon is not. It's so far away you couldn't see it with the naked eye if you were so unwise as to stand on the surface of Europa or Io and look for it.
    • So Jupiter is just a ... slut?

  • Could this be a recent moon? (Score:3, Interesting)

    by sielwolf ( 246764 ) on Saturday December 28, 2002 @11:44AM (#4972310) Homepage Journal
    How possible is it that this moon was recently captured in Jupiter's gravity (say in the last few years)? Maybe this could explain it's eccentric orbit (ie that it hit tangentally enough that it wasn't sucked in while not so shallow as to bounce away)? Does such a thing happen or am I blowing smoke out of my ass?

    *checks*

    Hmmm, no smoke yet.

  • Mmm. (Score:2, Interesting)

    by twiztidlojik ( 522383 )
    Just one question: when is an object considered a moon?

    I've tried the USGS, the IAU, and a general google search. This is going to annoy me to no end until I get an answer.

    • Re:Mmm. (Score:5, Informative)

      by mbone ( 558574 ) on Saturday December 28, 2002 @12:07PM (#4972377)
      Simple (more or less) - if it orbits another body (not a star), and is not man-made, it's a moon. Size is not really a consideration - if you can detect it, it's worth cataloging.

      I believe that Dactyl, the moon of the asteroid Ida, is only about 100 meters across.

      The exception occurs in planetary rings, where a moon has to be bigger than the ordinary rubble of the ring to be considered a moon.
    • it's if you lose it.
    • This is indeed a good question. Some people [space.com] have classified a stone that most of the time orbits sun and only part of the time orbits the earth, a moon of the earth. It seems that there is a continuum between moon orbits and these orbits, and it is possible that our moon will escape earth by using similar trajectory, and in the end being our moon and start orbiting the sun -- and possibly even collide the earth after that.

      Do not worry, that will not happen anytime soon. Moon's current escape rate is some 38 mm per year and the other smaller "moon" of earth is "safe" for the next 5000 years, too.

      There is also the J002E3, already though of as another moon of earth, but turned out to be space junk from the apollo program. Usually, natural moons do not have the spectral characteristics of titaniumoxide.

      • Some people have classified a stone that most of the time orbits sun and only part of the time orbits the earth, a moon of the earth

        Cruithne (pronounced croo-een-ya) doesn't really count as being a moon of earth's. It has a highly inclined orbit, and it never even goes around the earth. It's affected by the earth's gravity, but not in the normal way: because of the earth, Cruithne is in a horseshoe-shaped orbit around the Sun (it takes 770 years to go all the way around the Sun, but makes a single horseshoe orbit in less time). Strangely enough, it is also because of earth's gravity that Cruithne never goes around the earth: the combination of the Sun's gravity and the earth's gravity pulls it towards us, then sends it back the other way before it can get too close.

  • There are two moons yet to be discovered.. (Score:1, Funny)

    by Anonymous Coward
    You may ask how I might be aware of this ? Have you already forgotten the inevitable answer is 42.
  • I'm getting really tired about hearing all these new moons. First it's Jupiter, then it's Saturn. Oh wait, Uranus and Neptune have to get into the act. I think we just blow them up, the moons not the planets. Gotta be careful though when blowing up a moon. Especially if it's too close to one of those gas giants. They are full of highly flammable hydrogen and we wouldn't want to accidentally set one of them on fire. They'd probably burn a really long time like one of those garbage dump tire fires. Those really stink.

    It's a never ending moon's race. All these big planets do is keep capturing wandering asteroids and make them moons. It's not like the asteroids wanted to become a moon. They were perfectly happy just orbiting the Sun by themselves. I think we as the human race should collectively drop our pants and show those big planets that we have 6 billion moons. That'll show them. Right!

  • Wow, another moon of Jupiter discovered! Who would have thought? Even my astronomy professor says the whole Jupiter-has-a-lot-of-moons thing isn't very interesting (but that may be because it gets more press than his research, or maybe because he has to compete with those guys for timeshares on the Mauna Kea observatory).
  • In the future asteroids will be hauled into orbits for mining purposes. Maybe not Earth orbit...but wherever our mining colony might be. Considering that the new Jupiter discovery is only 3km, our new moons would be much larger.

  • This just in . . . (Score:3, Funny)

    by Lagrange5 ( 267948 ) on Saturday December 28, 2002 @01:09PM (#4972587)
    Astronomers have discovered two new specks of Jovian dust, JM20022812174130 and JM20022812174130A, which are Jupiter's 84,519,786,014th and 84,519,786,015th moons, respectively.

    Scientists are now beginning the process of officially naming the two new worlds. This is expected to pass through several committees before signature in March 2007.

    With the discovery, Jupiter is now 3,845,108,491 moons ahead of closest rival Saturn in the race for biggest posse in the solar system.
  • Here is a link to an intersting chart with orbital data for all moons in the solar system, including S2002 J1.

    Planetary Satellite Mean Orbital Parameters [nasa.gov]
  • Assume a defensive position and brace for incoming "That's no moon..." jokes!
  • At what point is something no longer called a "moon" and just given the title "Debris"? 3km sure is small.
    • Try saying that after being hit with it. Its so very humanocentrically egotistical to call something 3km across small while being 0.002 km across (measured the long way).
      • I'm calling something small which is thousands of times my size. Isnt that the very oposite of putting humans first on the list? Where the fuck do you find anything remotely human-related in that? Have you taken a look at our solar system? Things are pretty fucking large out there. I wouldnt call a stray human being flung around a planet a moon, but my question is 'is there someone who might?' What is the cutoff? 3km, compared to any other body in the system, is REALLY FUCK'N SMALL.
        Humans are too small to even bother noting the existence of.
  • ...a large black obelisk orbiting Jupiter.
  • After reading all these posts saying that anything orbiting a planet should be considered a moon, i'd like to point out that there are Jovian rings. Should we count all the little chunks of rock and specks of dust as moons too? Aren't a lot of these moons we've found just bigger chunks of rock in the rings?
  • ...that it's not another clump of rubble? The Story [sciencedaily.com]
  • I would of thought with all the powerful telescopes they have and with several orbiters that have travelled throughout the solar system that these kinds of discoveries would of been made decades ago? I thought that there was nothing more to discover in our solar system other than exploring planets and moons - not discovering new ones. Does mean astronomy is still in it's very immature stages? It might be hard to measure that due to the [unknown] size of the universe and limited space travel.
  • I'd hate to do this, but I read this slashdot headline to my 'lil brother "New Moon of Jupiter Discovered" and he corrected me: 'Moon' is the name of the satellite that orbits the planet Earth... So we've discovered a new satellite of Jupiter... I don't mean to nitpick, I just don't want you to embarass yourself in front of your little and more linguistically aware little brother.
  • That is, if you count each particle in the rings larger than 1 cubic centimeter

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