You’ve probably read about this unprecedented visitor from inter-stellar space.  I thought you’d like to see its trajectory through our solar system.

Oumuamua space diagram

(Enlarge as much as you can.)

My diagram shows the paths of the four inner planets in October, November, and December of 2017.  The path of Oumuamua is shown from August onward, in magenta before its 2017 Oct. 19 discovery, and then in yellow.  Stalks connect it to the ecliptic plane at the beginning of each month.

It arrived from the north, at an angle of about 33° (its “inclination” of 123°, or 90°+33°, means that the direction is retrograde – opposite to the general motion of the planets).  As with all travelers on huge orbits, like long-period comets, only the innermost, shortest, speediest part of the orbit is on the other side of the plane.

It descended through the plane on Aug. 24, inside the orbit of Mercury; was at perihelion (closest point to the Sun) on Aug. 30.  If you look closely you can see a sunward tick at that point.  It ascended back through the plane on Oct. 13, well outside Earth’s orbit.

It was nearest to Earth (0.276 a.u.) on Oct. 8.  A green line connects it to Earth at the nearest moment, which was some days before the discovery.

The view is from 15° north of the ecliptic plane, from a longitude of 350°, and from a distance of 6 astronomical units (Sun-Earth distances).  The planets are exaggerated 500 times in size, the Sun 5 times.  The dashed line shows the vernal equinox direction (the zero point for sky mapping).

That’s enough for now.  It was easier than I expected to find orbital elements and make them work, but I’ve had to spend more than half the day (the day before Christmas).  There is of course more to be said about this 250-yard-long hurtling red rock that has been given the Hawai’ian name ‘Oumuamua, and I expect I” say may some of it tomorrow or the day after.


20 thoughts on “Oumuamua”

  1. Most likely this is just a rock. On the off-chance this is discarded deceleration booster, is anyone looking back along the trajectory?

    The payload would arrive after booster.

    1. I doubt it. Even entertaining the fanciful possibility that it was a deceleration booster, the payload itself is likely just as small. The only reason we were able to spot 1I/Oumuamua is that it passed very close to Earth, and Earth has moved on in its orbit since then. If the payload is following the same path, it’s going to be quite a way away from Earth and not likely to be detectable.

  2. Can anyone generate an image that doesn’t look like the ship is accelerating? The perspective is grossly misleading on every graphic.
    It looks like the center of mass is between mercury and earth.

    1. The asteroid is accelerating. The Sun pulls it, speeding it up on the way in, and slowing it down on the way out. Some perspectives make it seem like the outward-bound journey is faster than the inward-bound. Think of a car approaching you at 40 mph, then making a sharp right turn and traveling tangential to you at 40 mph. No change in speed, but it sure seems like it sped up.

      Here is a simulation where you can choose any perspective you like to minimize or maximize this effect:

  3. Sorry Guy,it’s been quite awhile since my last post,”Life and all that !.” but I have managed to keep up with your E-Post.Just wanted to wish you and your good wife a very happy holiday and new year!. Sam

    1. The figures you’ve seen are presumably updated revised by someone, hopefully a professional. Mine just result from the orbital elements I found, which could have been put up earlier.
      When I tried to open the link you gave, I got some message about Sky Broadband blocking it.

  4. I like the name, ‘Oumuamua. According to Kelly Beatty in Sky and Telescope, ‘ou means “to reach out”, and mua means “first”. Repeating mua emphasizes the firstness of this reaching out.

    But I expect that the new object category “I” for “Interstellar” will cause confusion. It looks too much like the number 1. “E” for “Extrasolar” would work just as well.

  5. When I first heard about Oumuamua in late October, I ran the ephemeris in AstroGrav and it came out with the orbit very much like what we see today with better elements. It showed the orbit as strongly hyperbolic. Great software.

  6. One thing just for fun I wondered was some of the other milestones when it crossed say Neptune orbit, close to any famous comets, were it trajectory was from and going to.. It speed though the solar system. just some thoughts

  7. When I first read about Oumuamua I was struck by how closely its dimensions were to an Iowa-class battleship (the battleships are a little bit longer).
    Of course it’s nowhere near the size of Arthur C. Clarke’s “Rama”. That visitor to the solar system was about 20 X 50 km!

    Any reflections Guy on the Equation of Time and the odd interregnum we’re in right now between the earliest sunset and the latest sunrise?

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