Jupiter gets two more moons

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Astronomers using ground-based telescopes have identified two more moon circling Jupiter, bringing its total now to 69.

Both of these discoveries, as with the vast majority of Jupiter’s moons, occupy retrograde orbits, with inclinations greater than 90°, meaning that they move in directions opposite that of the planet’s spin. These distant, irregular orbits imply that these bodies formed elsewhere in the outer solar system and were captured while passing by early in the planet’s history.

A number of the moons recently discovered have since been lost because their orbits were too poorly constrained. However, some of these lost moons have also be recovered.



  • wodun

    Lost as in the astronomers lost sight of them or lost as in they are no longer Jovian moons? Tracking a moon flung from orbit would be a worthy project, if it is possible to do.

  • wayne

    I take it to mean “lost sight of,” but…. an excellent question!
    In the article they say–
    –“orbits known so poorly that they’re considered “lost.”” and linked off that phrase points to a 2012 S&T article–

  • wodun: Astronomers did not gather enough information to keep track of them. Click on the link, the story provides all the details.

  • wayne

    This is all, amazing stuff!

    serendipitously– I’ve been reading a copy of Sky & Telescope, from June 1967. The hardware & gadgetry prices are amazing, and a feature story includes “Surveyor 3 On The Moon.”
    I sorta naively assumed there was an on-going, dedicated effort to study Jupiter, in this manner. (We are funding tranny-dimensional, feminist particle-physics, but we are losing track of objects orbiting Jupiter. I would put forth the proposition; our priorities are messed up.)
    tangentially– we have an absolutely beautiful sky over the SW Michigan shoreline tonight.
    The Moon is yuuuge & remarkably 3-dimensional through my binoculars.

  • eddie willers


    It needs to gain or lose one or all the other planets will laugh at it.

  • LocalFluff

    Shouldn’t half of the captured moons be in retrograde?

  • Edward

    LocalFluff asked: “Shouldn’t half of the captured moons be in retrograde?

    Nice question. I have not studied the topic of captured moons, but if more captured moons favor one direction over the other, then there may be an orbital mechanics effect of moon capture that favors one direction over the other.

  • LocalFluff

    I think I get it now. The retrograde moons of all the gas giants all also have quite eccentric orbits. At longer distances, beyond about half the Hall sphere i.e. the gravitational dominance of the planet over the Sun, circular prograde orbits are very short lived. Even as short as 40 years. The pull of the Sun adds up for every orbit until they leave the planet. High inclination is of course less sensitive to the Sun and other planets and large local moons formed along with the planet in the ecliptic. And retrograde orbits are less likely to get into any kind of resonance that would evict them. I suppose this is the reasoning behind the Oort Cloud (still never observed) that should consist of comets in highly inclined orbits near the border of the Sun’s gravitational dominance.

    DRO, Distant Retrograde Orbits, are stable orbits for spacecrafts around our Moon. The ARM asteroid boulder was supposed to be placed in such an orbit, and I think it is an option discussed for the fantasy Gateway Space station to nowhere.

  • Edward

    Thank you for doing the research and posting the information. As you can see, orbital mechanics gets pretty interesting, especially when there is a third body pulling and tugging at the satellite/moon/planet (the second body).

    The Oort Cloud is just a region of space. What has yet to be observed is anything orbiting the Sun within that region, which is the reason for proposing the Oort Cloud.

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