Quasi-Moon 2016 HO3

Enough of politics. I’ve had more than enough of it.

Instead I’m going to write about newly-discovered asteroid 2016 HO3 that is circling the Earth.

Astronomers found a small asteroid circling around the Earth. Estimated to be between 40 meters (120 feet) and 100 meters (300 feet), the asteroid is now named 2016 HO3.

Scientists say 2016 HO3 is too far to be considered a true satellite of Earth, like the moon. Instead, they call 2016 HO3 as the best example of a quasi-satellite or near-Earth companion we have found so far.

The difference between quasi-satellites and true satellites is the time they take to loop around Earth. A true satellite should only loop within a few months or less than a year but it takes quasi-satellites a year to loop around Earth completely.

A week or two back I got hold of state vectors – position and velocity on a given date – for 2016 HO3 from NASA’s Horizons website, and plugged them into my orbital simulation model of the Sun and all the planets. Here’s a view of its orbit around the Earth as seen from the Sun over one year:


The black line is where the orbit is above the ecliptic – the planetary plane -, and the orange line is where the orbit is below the ecliptic. The horizontal smudge in the middle is the path of the Moon around the Earth. The Moon is roughly 450,000 km from the Earth. 2016 HO3 never gets nearer than about 20 million km from the Earth.

So it’s certainly going round the Earth, and taking almost exactly one year to do so.

But is it going round the Earth in the same way that the Moon does, drawn by the Earth’s gravitational attraction?

One way to test this is to reduce the Earth’s mass to 1 kg, and see whether it has any effect on either satellite. When I do this with the Moon, it immediately stops going round the Earth, moves quickly away, and becomes another satellite of the Sun.

But when I did this with 2016 HO3, it carried on going round the Earth in almost exactly the same orbit as before, going round and round the Earth just as shown above. So even with its correct mass, the Earth is having only a very small effect on it.

And that’s really because 2016 HO3 has an orbit round the Sun which is almost exactly the same as the Earth’s, only slightly more elliptic, and tilted slightly more to the ecliptic. Both the Earth and 2016 HO3 are taking 365.25 days to go round the Sun, and they’re always quite near each other. And they’re also far enough apart for the Earth’s gravitational influence to be tiny.

But it seems that the small influence of the Earth is going to be enough to keep 2016 HO3 from drifting slowly away for the next several hundred years (although I didn’t try to check that with my model, because it would have taken a long time). It’s going to be around for a long time.

I think they should give it a better name than 2016 HO3 if it’s going to be going round us for hundreds of years. Since it’s only been in this quasi-orbit for 100 years, it might best be named after some “star” born in 1916. Like film star Betty Grable. So my suggestion would be to call it Grable. Or BettyGrable. Or maybe just Betty.

I hope that made a welcome change from writing about all the mad, infuriating things happening on our little spinning planet. Or at least put them in a different perspective.

About Frank Davis

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8 Responses to Quasi-Moon 2016 HO3

  1. Harleyrider1978 says:

    Really the politicians are all in orbit anyway

  2. Tony says:

    A Mars like body/planet called “Theia” supposedly collided with the Earth about 4.3 billion years ago. The moon is supposed to be made from the collision debris.

    I always wondered what happened to the rest of this body and intrigued that the Martian day is almost exactly the same length as an Earth day (24.026 vs 24.0 hours). A coincidence? I have no idea.

    Hearing that 2016 H03 takes exactly 356.25 days to go round the Sun makes me wonder if it is part of the Theia collision picture.
    Just idle speculation, if I dare use that word here :)

    • Tony says:

      Oops, I should have said the length of a Martian day is 1.026 Earth days not 24.026 hours. That doesn’t alter my point though.

  3. garyk30 says:

    If one thinks in 3 dimensions, Betty’s path is more elegant than just an eclipse around a point.

    Her path is a spiral around the Earth’s path around the Sun.
    The Earth will move about 575 million miles during her orbit.

    The Earth’s path is a spiral around the Sun’s path as it orbits the Galactic center.

    The Galactic Center changes position as the Galaxy speeds outward from the Big Bang point.

    Thus, one has a spiral around a spiral around another spiral path.
    I think this makes a very elegant concept.

    I suspect that a video of the motions involved would difficult to make.

    A curious point about motion is that in the course of a year, our position in space changes by about 16.5 billion miles.

    The Earth speeds around the Sun at about 65,585 MPH.
    The Sun speeds around the Galactic Center at about 490,000 MPH.
    The Galctic Center speeds along at about 1.34 million MPH.

  4. smokingscot says:


    Okay I know you wanted to keep clear of politics… but.

    GEORGE OSBORNE has quit both as Chancellor and as part of government!!! In short he’s – correctly – demoted himself to the back benches.

    Philip Hammond, who I made mention of a couple of days back, now occupies 11 Downing St.


    And twice over the last couple of days Mrs. May has stated:

    “We will give you more control over your lives.”

    Now if she wouldn’t mind repeating that one more time to Jerry Fisher and down there in Poole.


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