back to article Earth's wobbly companion is probably the result of a lunar impact, reckon space boffins

A freshly discovered train-sized rock that tags along with Earth as a constant companion orbiting the Sun is most likely a fragment of the Moon resulting from an ancient lunar impact. 469219 Kamo'oalewa – discovered by observers in Hawaii in 2016 – is about 41 metres in diameter and orbits the Sun in a trajectory not …

  1. herman Silver badge

    Far out man

    14.5 km away is pretty damn close. We should fit a transponder on it so that aircraft can turn in time.

    1. Version 1.0 Silver badge

      Re: Far out man

      14.5 million km ... not 14.5 km.

  2. ArdentSceptic

    Really far out

    Never closer than 5,210,000 km is the true figure... and a little better than 14.5 km...

    1. diodesign (Written by Reg staff) Silver badge

      To clarify:

      The MOID is 5.2 million km, and for those of us who aren't astronomers, in practical terms, the closest the rock and Earth get is 14.5 million km.


  3. Anonymous Coward
    Anonymous Coward

    Looks like a nice place to put an observation deck

    with a bar, of course.

    1. jake Silver badge

      Re: Looks like a nice place to put an observation deck

      I'll bet you say that to all the pretty space rocks.

      1. DJV Silver badge

        Re: Looks like a nice place to put an observation deck

        And then he tries to get them stoned... (gets coat).

        1. adam 40 Silver badge

          Re: Looks like a nice place to put an observation deck

          It would have to be a Hard Rock café.

  4. Version 1.0 Silver badge

    Look at the moon, then look around

    The moon is covered in massive craters from strikes going back about 4 billion years, the earth has probably had a similar number of strikes but the majority of them have been hidden by the way our world has evolved over the same period of time - the dinosaurs were removed by a large strike about 66 million years ago but we have to dig down into the earths crust to verify that it happened. Until quite recently we all thought:

    You know tyrannosaurus rex was destroyed before, by a furry little ball that crawled along the primeval jungle floor. He stole the eggs of the dinosaur." - Jefferson Airplane Mau Mau (Amerikon)

  5. KBeee Silver badge

    What I want to know is

    Were any Clangers or Soup Dragons harmed during the creation of 469219 Kamo'oalewa?

    1. Twanky Silver badge

      Re: What I want to know is

      Harmed? No - it's part of their invasion plan.

      More blue string pudding anyone? I for one welcome...

  6. Neil Barnes Silver badge

    habit of dwelling in the darkness of space

    Sorry. Just wanted to enjoy that phrase again.

  7. jollyboyspecial Bronze badge

    Train sized?

    I've certainly never seen a train with a 41m diameter

    1. Anonymous Coward
      Anonymous Coward

      Re: Train sized?

      It's not the girth it's the length that matters.

  8. Brewster's Angle Grinder Silver badge

    Horse - optional

    It's impressive that that orbit is in any way stable.

    1. Anonymous Coward
      Anonymous Coward

      Re: Horse - optional

      Tell that to all the neigh-slayers out there

      1. jake Silver badge

        Re: Horse - optional

        I hate to beat a dead horse, but that might involve a surcingle argument.

        1. adam 40 Silver badge

          Re: Horse - optional

          I'll have to put a halter these terrible puns.

          1. jake Silver badge

            Re: Horse - optional

            We should have a straw poll ... do we continue to saddle the commentariat with such flights of fancy, or should we rein them in?

          2. Andy Non

            Re: Horse - optional

            Too late to close the stable door.

  9. Anonymous Coward
    Anonymous Coward


    The animation says "Half the time, it's orbit takes it closer to the sun and it passes ahead of the earth. The other half of the time it is farther from the sun and calls behind"

    Um.. Isnt that true of everything that orbits the Earth???

    (Anon. because I'm probably being stupid and you'll all laugh at me, as I will deserve!)

    1. mr.K

      Re: Huh?

      I think the simplest answer is that a true satellite lies within what they call the Hill sphere. The Hill sphere to an object is the region where its gravity dominates. Remember it is quite far out, around 0.1 AU. Both of us “just happen” to orbit the sun in the two different orbits with the same orbital period and about the same place in the orbit. Remove the sun and I think we would just drift apart.

      1. Anonymous Coward
        Anonymous Coward

        Re: Huh?

        Ahhh, I gotcha. Thanks.

        I misread the article, I thought it said the thing orbited the earth not the sun, which is why I thought the description in the video was a bit superfluous.

      2. ThatOne Silver badge

        Re: Huh?

        > Remove the sun and I think we would just drift apart.

        Happens to all holiday flings...

      3. the small snake

        Re: Huh?

        Hill sphere of a body is defined by other massive bodies near it. For the Earth that means, mostly, the Sun. If you removed the Sun Hill sphere of Earth would change radically (it would get much larger). Body might then be within this new sphere and might have less than escape velocity, so might very well then be orbiting Earth-Moon system. Too lazy to do the celestial mechanics to work that out.

    2. Scene it all

      Re: Huh?

      There are two tiny moons of, I think, Saturn, that do the same thing. They swap positions from time to time without ever colliding.

      What caught my eye about this rock was how it had reddish coloration and this led them to think it was Lunar in origin. But Omuamua, the recent interstellar vistor, ALSO had red coloration, and so does Arrokoth, the peanut-shaped Kuiper Belt object recently visited by the New Horizons spacecraft. It looks like reddish hues are common for rocky objects subject to very long term cosmic radiation.

      So being in such a close orbit to Earth is probably a better argument for being a result of the Earth/Theia collecition that created our Moon, than any particular surface chemistry.

  10. Winkypop Silver badge

    It would make a great base for our spacefaring billionaires


    1. jmch Silver badge

      Re: It would make a great base for our spacefaring billionaires

      On a 41m diameter rock ??

      I'm sure the view is fantastic but my yacht's bathroom is bigger than that!


      1. jake Silver badge

        Re: It would make a great base for our spacefaring billionaires

        Our pub is clearly a lot more discerning than the head in your tupperware toy.

  11. Little Mouse Silver badge

    So where does that leave us?

    Technically speaking, should the Earth still be classed as a planet if it hasn't cleared its orbit of space-detritus?

    1. the small snake

      Re: So where does that leave us?

      This thing is a quasi-satellite of Earth: it is where it is only because of Earth. Further it is not clear how stable the system is. It has been there only perhaps for a century or so and will probably remain for some centuries more. But probably not for very long at all. Has been previous body doing similar thing: it's gone now and only was there for decade or so I think.

    2. Brewster's Angle Grinder Silver badge

      Re: So where does that leave us?

      The trojans are going to blow your mind!

  12. Phil Kingston

    Don't know about you

    but i want to visit a town called Happy Jack

    1. jake Silver badge

      Re: Don't know about you

      Maybe not ... it was originally called Yellowjacket for a reason, and it's a long way from the nearest cold beer. Note that the telescope is not open to the general public. If you are interested in that kinda thing you'll want to visit their main campus at Mars Hill, Flagstaff Arizona. Well worth the trip, recommended.

      1. KBeee Silver badge

        Re: Don't know about you

        Sounds a bit like how the Cape of Storms became the Cape of Good Hope.

        Change the name, change the perception.

        Though if they'd changed it to the Cape of Good Hope Blockchain it'd be worth 10X as much

  13. G R Goslin

    A fragment? I think not.

    Planet sized objects tend to act as liquids, more than solids, The strength of the crustal materials are as nothing to the forces available in a collision. What comes out of the collision is either liquid, gas or comminuted debris. Given time, since they all tend have a common velocity, they could coalescs under the common gravity field, but it would not be a fragment in the sense of being a broken off bit of either the impactor, or the impacted

    1. the small snake

      Re: A fragment? I think not.

      This is a slight confusion. Planets are indeed essentially liquids: this is why they are spherical (apart from very spinny ones). but this is on large scale: on small scale material near surface (and further down than that for The Moon) does not act like liquid (neither does for instance, clump of 100 water molecules probably).

      What comes out of collision is lots of chunks of stuff including dust, gas, probably actual molten rock and so on. On large scales these will coalesce into other body and behave as liquid (if giant impact hypothesis is correct The Moon is one such body, coalesced from bits of pre-Earth and whatever hit it).

      On small scales – scale of bus or building say – these chunks do not behave like liquid, and chunks this size may be ejected, and may avoid coalescing. This is such a chunk.

      Other good example are Martian meteorites.

  14. J.G.Harston Silver badge

    I'm now picturing setting up base on a Trojan asteroid and jumping off to other asteroids, tying a rope to them, and pulling them in to gather them together.

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