back to article Sky boffins: The Moon is not Earth's only natural satellite

The Moon is not alone in its role as the Earth's natural satellite, although its companions are tiny fellows who usually don't stay long. "At any given time there is at least one one-meter-diameter object orbiting the Earth," three astronomers write in the abstract of their article, "The population of natural Earth satellites …


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  1. David Webb


    I'm sure this was a question on QI a few years ago, how many moons does Earth have and the answer was 2 or 3 or so.

    1. Sorry that handle is already taken. Silver badge

      Ahh, QI

      Yes, they said Earth has two moons. They were wrong.

      For reference, the not-second-moon is Cruithne.

      1. Vic

        Re: Ahh, QI

        > Yes, they said Earth has two moons.

        There was a follow-up question in a later series that took it up yet further.

        > They were wrong.

        Stephen Fry? Wrong? How could you possibly insinuate such a thing. Next, you'll be telling us that GPS receivers don't transmit to the satellites...


        1. This post has been deleted by its author

          1. Cameron Colley


            I don't understand this negativity.

            The GPS thing was stupid, admittedly, but how many people knew what Cruithne before they watched QI? I'd not consider myself overly educated but I'm by no means uneducated and I'd not heard of it. Once I had, of course, I realised it wasn't a moon but I think that's part of the fun of QI.

            QI is an entertainment programme which makes one think, why is that irksome?

            As to Mr Fry, I don't see that the GPS explanation has anything to do with him. They will likely have script writers fro that kind of thing but if it was an off-the-cuff remark on his part the blame lays with whoever decided to broadcast it. I'm not suggesting that Mr Fry necessarily does know how GPS works but referring to an edited television programme as evidence is stupid.

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              1. Cameron Colley

                Re: @Cameron

                For the most part I think you will find that the questions on University Challenge were "trivia" so, frankly, I am as unimpressed that Mr Gascoigne researched the questions as I am by Mr Fry's technical ability. They are [were] television programmes made to entertain and, sometimes, impart a little knowledge or get one thinking.

                If I want dry science I know where to find it, but reading Scientific American from cover to cover doesn't particularly interest me any more -- I hope that doesn't make me a bad person? I gave up on New Scientist when it turned into "Politics Today" a decade or so ago.

                As for venerating Mr Fry's technical knowledge, I would never do such a thing as I know that he is not a technical man and doesn't profess to be -- he's a presenter of an entertainment program. I mentioned the GPS debacle because those were words "put into his mouth" and I feel that people judging him by them are as ignorant of how things work as those who think he's a genius.

      2. Sorry that handle is already taken. Silver badge


        I shouldn't have started that.

        For reference I enjoy watching QI.

    2. Eddie Edwards

      Re: QI

      Even if the Earth did have more than one natural satellite, asking how many moons it has is like asking how many Atlantic Oceans it has.

      1. Anonymous Coward
        Anonymous Coward

        Re: QI

        "Even if the Earth did have more than one natural satellite, asking how many moons it has is like asking how many Atlantic Oceans it has."

        How many moons called The Moon would be one. We could still have more than one moon though just as the other planets of our solar system have many moons, none of which is called The Moon however.

  2. Anonymous Coward

    I don't get it...

    If a moon(let) has been captured and then hangs around the earth for a decade, I don't see how it can gain the velocity to escape again. Is it being pulled awy by the sun, the moon, or a Martian energy beam?

    1. Aqua Marina

      Re: I don't get it...

      Frickin lasers!!!

    2. Gordon 10 Silver badge

      Re: I don't get it...

      Some orbits are more stable than others.

      Imagine a swing - if you inject the same energy time and again the swing goes higher. Similar thing here but the energy is being injected by the Earth, Moon and Sun.

      If it helps bear in mind even the moons orbit is very slowly changing.

    3. CaNsA

      Re: I don't get it...

      Something to do with the pull from the sun, the earth and the moon creating the slingshot effect.

      It's only a matter of time before the mini-moon has enough speed to break free..... just like Freddie Mercury.

    4. Anonymous Coward
      Anonymous Coward

      Re: I don't get it...

      As others have stated there are many way this is possible.

      For instance our "real" moon is slowly escaping the earth, it is just doing it by a few cm a year.

  3. tweell

    Eleanor Cameron was right

    The Mushroom Planet exists!

  4. h4rm0ny

    That's one Hell of a sharp turn near the start

    In fact, the whole path is a lot crazier than I find intuitive.

    1. Will Godfrey Silver badge

      Re: That's one Hell of a sharp turn near the start

      Looks stranger than it is because it's a 3D plot on 2D. That first loop is going mostly front to back.

  5. Richard IV

    January and July

    The preference for moon gathering during those months is probably not unrelated to the Earth's aphelion and perihelion being around then. You'd expect the zone in the middle of the orbital range to have been largely cleared or absorbed ages ago, or at least to a far greater degree than the edges.

  6. Malc

    Shurely some mishtake

    Is it just me, or does the mini moon's path not seem to hit Earth on its way out?

    (Just after it turns a darker orange)

  7. Christoph

    Moore's Law

    "If you were to try to do this on your home computer, it would take about six years."

    So wait about another three years, and it will only take you two years to run it.

  8. AceRimmer1980


    no moon.

    (but we have a space station)

  9. Anonymous Coward
    Paris Hilton

    they found a third, semi permanent moon years ago, have they still not given it a name??

    (I still have problems pronouncing "Cruithne."; so I hope they pick something easier.)

    PARIS, something to do with celestial bodies ;-)

    1. Anonymous Coward
      Anonymous Coward

      The Earth has one permanent natural satellite - the Moon. There are however a number of objects that are in 1:1 resonances with the Earth which are called quasi-satellites. The orbit of a quasi-satellite is not stable over the long term and the object will eventually go off into another orbit around the Sun.

      There are five quasi-satellites of Earth: 3753 Cruithne, 2002 AA29, 2003 YN107, 2004 GU9 and 2010 SO16. In 2002 the Earth temporarily captured J002E3 which turned out to be the third stage of Apollo 12 which had been discarded into solar orbit. After a few swings around the planet it was ejected into a new solar orbit.

    2. Jimbo 6


      It's pronounced 'Krin-ya'

      (In the same way that the Irish lame hippy chanteuse Eithne has her name anglicised as 'Enya')

  10. Some Beggar

    My spirograph is bigger than your spirograph.

    1. Anonymous Coward
      Anonymous Coward

      Yeah maybe... but I've got more coloured pens...!

      1. Some Beggar

        I'm not allowed coloured pens after I ate all the green ones.


  11. Cameron Colley

    When do they become "mini moons"?

    How many times do they have to go around the Earth to be classed as a moon then? Is a meteorite a moon, or a comet? Do they have to make at least one full revolution?

  12. Zaphod.Beeblebrox

    M O O N that spells moon!

    I would think that the definition of a moon would include that is is in a stable orbit of the planet, but then, I would have thought astronomers would have had a definition of "planet" before they came up with one that demoted poor Pluto.

    1. BristolBachelor Gold badge

      Re: M O O N that spells moon!

      I think that they had a definition of planet. The problem was that once they could see all the small (relatively speaking) rocks that orbit the moon, they realised they would have to upgrade the solar system from having 9 planets to more than 2 thousand.

      I guess that it made sense to draw the line somewhere about what constitues a planet, and loosing 1 (and the furthest one out) made more sense than suddenly adding lots of new ones, and the 6th planet out from the sun changing from the huge Saturn to something like the tiny (and catchely named) 303775. (Pedants need not point out that 303775 is probably not in the right location to be the 6th "planet", it's just picked out at random as a dwarf planet.

  13. Some Beggar

    And what happens

    if one hits your eye like a big pizza pie?

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