Talk:ʻOumuamua/Archive 3

This is an archive of past discussions about ʻOumuamua. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page.

Archive 1

Archive 2

Archive 3

Archive 4

Archive 5

Sky trajectory images

Trajectory motion from Earth, 7 days of motion per marker
Origin in direction of Lyra
Destination in Pegasus
Trajectory seen from the Sun
Shown from a fixed perspective above the Solar System

I finally got around to adding an import function for drawing orbital ephemeris from JPL's HORIZONS system. I need to validate it a bit, but seems to be good. So this shows its path viewed from the earth, with 7 days of motion, and yellow spheres proportional to angular sizes. So along with the pretty annual retrograde loops, you can see the source converges near Vega in Lyra, and the destination converges in the great square of Pegasus. It was closest to earth in Orion, but unfortunately before discovery. Tom Ruen (talk) 08:10, 1 December 2017 (UTC)

Nice diagram, and it must have taken a lot of work, but it is very easily misunderstood as its actual trajectory, and gives the impression of orbiting stellar objects. It could be a source of interpretational problems. BatteryIncluded (talk) 15:37, 1 December 2017 (UTC)

I like it. Just need to describe it as Oumuamua's motion across the sky. -- Kheider (talk) 19:42, 1 December 2017 (UTC)

Here's another quick one (unlabeled), motion seen from the sun although an impossible view, a simpler motion. Tom Ruen (talk) 16:10, 1 December 2017 (UTC)

Here's another shown from a fixed perspective above the solar system so the hyperbola focus is more clearly on the sun. Tom Ruen (talk) 20:58, 1 December 2017 (UTC)

The third one looks good. I'm glad that one was chosen over the others. I might tinker with it a little if you don't mind, Tom? nagual design 04:15, 2 December 2017 (UTC)

Sure. I can remake things differently as well. But I don't know where they are best in the article either. Where images are now don't really make sense. Tom Ruen (talk) 04:19, 2 December 2017 (UTC)

@Tomruen: Could you tell me on what date ʻOumuamua passed above the ecliptic and when it passed back through? nagual design 22:01, 2 December 2017 (UTC)

I've thought about visualization changes for above/below the ecliptic. It's easy to check the data by the declination sign. [1] Tom Ruen (talk) 23:01, 2 December 2017 (UTC)

Date__(UT)__HR:MN     R.A._(ICRF/J2000.0)_DEC  APmag            delta      deldot    S-O-T /r    S-T-O
2017-Sep-06 00:00     11 12 02.86 +00 05 24.6  21.05 1.25616963759190 -22.7910047   7.2618 /T  26.4403
2017-Sep-06 12:00     11 09 28.79 -00 22 10.4  20.99 1.24925834878085 -25.0964034   7.0888 /T  26.5352
And
2017-Oct-16 00:00     03 34 03.93 -00 28 31.6  19.76 0.16746168064530  15.8239045 146.1884 /L  29.1155
2017-Oct-16 12:00     03 11 51.39 +00 08 27.7  19.70 0.17285802437473  21.4683896 152.0566 /L  23.9058

Okay, thanks Tom. I found the videos and images online a little confusing. The ESO video appears to show ʻOumuamua approaching from beneath the ecliptic, but Scott Manley's video looks like it approached from above. Something akin to the Hollow-Face illusion going on, I guess.

So am I correct in thinking that it approached from above, dipped down between the Sun and the orbit of Mercury, then came back up between the orbits of Earth and Mars? nagual design 23:09, 2 December 2017 (UTC)

...Assuming that that was the case, I've uploaded a new version of the image. Let me know what you think. If you prefer, I can remove the glow from the Sun, or any other changes. nagual design 23:32, 2 December 2017 (UTC)

Its very nice as-is. Mine was purely computed except the labels. The under/over orbit lines are very helpful, so you don't need to know exactly where it crosses the ecliptic. Tom Ruen (talk) 01:47, 3 December 2017 (UTC)

Glad you like it, and that it's accurate. One small matter that irks me is the positions of the planets. Given the timescale involved (13+ weeks) Mercury would have made slightly more than one complete orbit and the Earth would have made a quarter orbit, which begs the question as to what date the planets were in those positions? It might me helpful if you add that information to the image file description (the caption in the article is fine as it is). Thanks, Tom. nagual design 16:18, 3 December 2017 (UTC)

Yes, it is confusing. The planets are positioned at perihelion. There's no clear right answer unless we don't draw planets OR label planets with a date, or possibly multiple dates. My program currently only selects a single object to draw a tracking path, but I could make multiple images, tracking different objects, if you wanted to rework some of them into one diagram. But since I don't save exact viewing locations, I'd have to tweak something approximately the same, and you might need to rework your version from scratch if not close enough. Tom Ruen (talk) 19:24, 3 December 2017 (UTC)

For clarity specifically, the perihelion positions could be drawn differently, equal circles, with smaller circles for the other dates of 'Oumuamua. And maybe showing a second earth position dated and labeled with that earth. Tom Ruen (talk) 04:05, 4 December 2017 (UTC)

I would have guessed that the planets are positioned at perihelion. I don't think there's a better way to draw it. Showing the direction of the planets' orbits helps to show that we're looking at the Solar System from 'above'. And the image is primarily an overview of ʻOumuamua's trajectory, so adding extraneous details would just make the diagram unnecessarily busy. S'all good. And now that I look I see that you'd already edited the file description long before I asked! Great minds think alike.

nagual design 04:19, 4 December 2017 (UTC)

Here's a similar diagram for New Horizons, File:New_Horizons_Full_Trajectory_Sideview.png which has same problem. Its solution is to show past path in green and future path in red, so you can assume the positions shown are where future and past cross, although didn't really have other dates labeled. But maybe I'll add something like that. Tom Ruen (talk) 01:59, 5 December 2017 (UTC)

The timestamp is shown in the corner of the image: "6 Sep 2017 04:00:00 UTC". And if you compare the current image for 6 September 2017 with a previous version for 10 September 2015 you can see that the planets have moved. Earth is in the same position since it's early September in both images. nagual design 02:18, 5 December 2017 (UTC)

Yes, so that confirms the planet positions are on the given date. I know what we need - we should draw a "tick mark" for the 7-day labeled date positions. Unlabeled tick marks on the earth would also help clarify its position and speed. Tom Ruen (talk) 03:50, 5 December 2017 (UTC)

I think it's enough to mention in the image file description, "The planet positions are fixed at the perihelion on September 9, 2017." As I said, adding extraneous details would just make the diagram unnecessarily busy. As long as anyone who wonders why the planets are where they are has access to that information we're golden. nagualdesign 04:29, 5 December 2017 (UTC)

FWIW, I like the first diagram (especially now I've noticed it shows the source/origin very close to the solar apex), and the 5th (that clearly shows between which orbits it passes). - Rod57 (talk) 16:51, 16 December 2017 (UTC)

origin

Just to not open another section, here is a new article on the ongoing efforts to figure its place of origin and systems it may have flown by: [2]. Cheers, BatteryIncluded (talk) 00:01, 3 December 2017 (UTC)

Nonsensical passage about "diameter"

The passage "230 m × 35 m × 35 m (800 ft × 100 ft × 100 ft) with an average diameter of about 110 m (360 ft)" doesn't make sense. Jim Bowery (talk) —Preceding undated comment added 16:01, 15 December 2017 (UTC)

Hi. Although not an addition of mine, I have now elaborated a bit with a proper wiki-link to 'apparent size'. But also a citation needed tag as none of the two refs discusses this issue. I think it is a useful piece of info, but it needs a proper source and I have not invested any time in that. RhinoMind (talk) 16:37, 15 December 2017 (UTC)

The proper portions of Oumuamua are simply not known. Is it 5:1 or 10:1? What is known is that the average size is around 110 meters or so. Astronomer David C. Jewitt lists an "average radius of 55 m". (Radius = "diameter/2".) This has nothing to do with apparent diameter as Oumuamua is nothing more than a point source in even the largest of telescopes. -- Kheider (talk) 17:20, 15 December 2017 (UTC)

Well, what does "average diameter" even mean if not apparent size? Also, Jewitt is the one who mentions the "30m x 30m x 180m", he doesn't talk about any average diameter of 55 m in the NOAO ref at all as you claim. If there is no ref to the 110 m and if there is no explanation of what "average diameter" means, we will have to remove the info from the article. RhinoMind (talk) 17:50, 15 December 2017 (UTC)

Apart from the Wikipeida stuff, I would also like to reply about basic astronomy. Even if an astronomical object appears as a point source - and many objects do - both apparent sizes and real sizes can be inferred from the study of light-curve variations. This is also the technique used for this particular asteroid, as described in the Astrophysical Journal Letters article. RhinoMind (talk) 17:53, 15 December 2017 (UTC)

The average diameter is based on their lightcurve study and albedo estimate. The abstract mentions the average radius. The Sun has an apparent in the sky (Angular diameter) of 32 minutes of arc, but that is not the Suns physical diameter. Does anyone bother to check references anymore? The real question is, "Should we quote a different paper using a lower albedo and thus a larger size?" -- Kheider (talk) 18:14, 15 December 2017 (UTC)

Ah yes. The "average radius" of 55 m is also deduced on p. 5-6 in the Astrophysical Letter.

But still, what does this "average radius" actually mean? It does not make much sense to mention it in relation to physical geometrical features without any explanation. The 55 m is not the physical radius of the object, but rather an abstract cross-sectional radius, assuming the object has a circular shape (which it hasn't in most cases, including this one). It is nice to work with this term theoretically, but it is not be used directly in relation to the physical geometry.

I am sorry to have linked to the obviously non-related concept of angular diameter. That was me being too careless. What I was thinking about, was the cross-sectional diametre, as I have also pointed out. We could perhaps link to that concept in the text to include at least some partial explanation to what the 110 m is all about, but even that would require some further extra explaining to make it meaningful to most readers.

Bottom line is, the 110 m is only vaguely related to the actual physical dimensions of the asteroid. It is a theoretical and partly abstract concept. It does not hold any useful information to anyone other than theoretical scientists. It is confusing to most readers and for all these reasons, I suggest we remove this piece of info from the article. RhinoMind (talk) 00:06, 16 December 2017 (UTC)

Another problem is that the object could be 200 meters x 40 meters (5:1) or 400 meters x 40 meters (10:1). The light curve is open to multiple solutions and is effected by potential surface albedo variations. The 110 meter average is more of a spherical equivalent. -- Kheider (talk) 01:10, 16 December 2017 (UTC)

....yes a spherical abstract equivalent of the cross section of the asteroid as seen from our point in space. It will vary as we and the asteroid move through space.

I take it that you agree to remove this piece of info then? RhinoMind (talk) 01:26, 16 December 2017 (UTC)

No. The whole diameter issue should probably be better written as the precise size is unknown. All we know is that it is a tri-axial ellipsoid with dimensions a×b×c. We know that b is ~40 meters, a>5b, and b≥c. The average diameter will vary less than the multitude of triaxial ellipsoid solutions. -- Kheider (talk) 09:01, 16 December 2017 (UTC)

If info about the "average diameter" is to be kept, it should at least be explained in the article what it really means. It is a source of confusion and misunderstanding on its own. Could you perhaps write a few words about it in the article? RhinoMind (talk) 12:33, 16 December 2017 (UTC)

See Diameter for a generalised definition of diameter for irregularly shaped objects, it's basically the maximum distance (technically the supremum) between any two points inside the object. So the passage may be confusing rather than nonsensical. It's not sure that's what is meant though. Martijn Meijering (talk) 12:43, 16 December 2017 (UTC)

I wouldn't use a mathematical generalization here. Astronomically an estimated average diameter would be a time-averaged cross sectional area observed and mapped onto a circle of the same area. Or more simply it estimates what diameter diffuse sphere of the same albedo would have the same average brightness. Tom Ruen (talk) 13:09, 16 December 2017 (UTC)

Certainly do not use the "generalized definition", that would make this object up to 400 meters in diameter, larger than 90% of the asteroids in the solar system. (common knowledge, no citation needed) The 110 m "number" is larger than 75%.User-duck (talk) 17:09, 16 December 2017 (UTC)

"time-averaged cross sectional area observed", do any of the references use this phrase (or a reasonable close one)?, I did not notice it. I am pretty sure I understand the concept, is there a wiki article so I can verify my interpretation.User-duck (talk) 17:09, 16 December 2017 (UTC)

Assuming the info is in Jewitt's https://arxiv.org/abs/1711.05687 abstract (I personally need to verify), The derivation would have been "(15 + 90) / 2 = 52.5 → rounded to 55". This is not the calculation used in the Asteroids article which uses three axes (really axes), the derivation would then be "(15 + 15 + 90) / 3 = 40". I can't add this tidbit since it is obviously OR.User-duck (talk) 17:09, 16 December 2017 (UTC)

I am planning on constructing a table with all the estimates (guesses?) to see how it looks and if it might help with this very confusing info.User-duck (talk) 17:09, 16 December 2017 (UTC)

From where and to where

This is OR< so it can't be included in the article. The furthest forward NASA's Horizons will go to is the year 2500, which lists its position as 23h 52m +24 43', inside the Great Square of Pegasus, close to Alpheratz, about 1/4 of the way into the square. THe furthest it goes back is 1600, which lists it position as 18h 39m +33 58', which is indeed very close to Vega. — Preceding unsigned comment added by 120.154.41.89 (talk) 07:12, 4 December 2017 (UTC)

As Oumuamua gets further from the Sun, it really will NOT be moving relative to the background stars. We have numerous sources that state it is headed towards Pegasus. PS: I would like to see the solar apex also labeled. -- Kheider (talk) 14:10, 4 December 2017 (UTC)

I added a purple circle at the solar apex. Tom Ruen (talk) 08:49, 5 December 2017 (UTC)

Interesting it came from very near the solar apex and the 66 degree turn towards Pegasus seems to be sending it away from the galactic center in Sagitarius. An animation in galactic coordinates showing just the sun and Oumuamua might be interesting ? - Rod57 (talk) 17:29, 16 December 2017 (UTC)

Dimensional ratios

There's reason to wait for "final best estimates" if such a thing is possible, but seeing the artistic image as grossly exaggerated, I attempted a rescale by 65% shorter length, so its closer to the 180x30x30m dimensions given in this article. Tom Ruen (talk) 18:53, 22 November 2017 (UTC)

I think as more time passes the calculations of the shape of this object will shift to a less cylindrical model. Will have to wait for those RS estimates.

I see someone inserted my compressed image to the stat table, while the "In the news" image is still the crazy long original one. Tom Ruen (talk) 15:51, 24 November 2017 (UTC)

What about eso1737e? Askaniy (talk) 14:01, 26 November 2017 (UTC)

I'd say let's just wait and see. Tom's edit, currently in the infobox, closely matches the 6:1 ratio that's the current best estimate. Given that the oscillating light curve on which the estimate is based might just as easily be caused by a (more) spherical two-tone object we're talking about giving form to something that's largely guesswork, and I'd recommend against any action that might imply an increased sense of certainty. In other words, each time we update the infobox many people might mistakenly believe it to be based on new evidence, which it isn't. nagual design 17:34, 26 November 2017 (UTC)

I just noticed this section now. I don't see an explanation of the variations but presume these represent the upper and lower limits, which makes more sense than the long one alone. Tom Ruen (talk) 07:58, 7 December 2017 (UTC)

long or flat? The eso1737a artists impression] could be the side view of a flat plate. The arxiv reports both seem to have assumed a prolate shape. Do they say why they don't consider Oblate spheroids ? Are oblate asteroids very rare ? (any triaxial ellipsoid 10 > X > 1 could give a 1:10 brightness ratio ?) - Rod57 (talk) 18:39, 16 December 2017 (UTC)

Colour

Since spectroscopic analyses of ʻOumuamua have resulted in it being classified as spectral type RR (very red, same as Sedna) would it be a good idea to update the image? I have a version ready to upload based on Tom's edit, broadly similar in colour to File:Artist's conception of Sedna.jpg, but I thought I'd better ask first. nagualdesign 18:38, 10 December 2017 (UTC)

..Okay, since I'm a bit peckish I went ahead and uploaded the file as a separate image. I also updated Tom's version, since I had to rework the image from scratch before altering the colour and the new version was higher quality (sharper). I hope that's okay. The only question now is whether to add it to the infobox. I'm off to make something to eat. nagualdesign 19:08, 10 December 2017 (UTC)

I'm not sure what is best. It looks like its tinted red mostly in the (imaginary) ambient shadow lit side, as-if was being lit by a full Mars off the view!?! Tom Ruen (talk) 19:36, 10 December 2017 (UTC)

Specular highlights are largely the same colour as whatever light source they're reflecting, which in this case is the Sun. Since ʻOumuamua is thought to be of high metallicity I thought it might well be quite shiny. I tried various amounts of colour, including making almost the entire thing reddish, and it didn't look right to my eye. If you like I can add more colour to the sunlit side. My tea's in the oven so it might take me a while. nagualdesign 19:52, 10 December 2017 (UTC)

I wouldn't have presumed the reflections were specular, but an open question to be sure. I uploaded one that is tinted red all over, lower quality since I reworked it quick. Tom Ruen (talk) 20:26, 10 December 2017 (UTC)

I tried one more, darked the fake ambient shadow light. Tom Ruen (talk) 20:37, 10 December 2017 (UTC)

Sorry Tom, I overwrote your edits without even noticing them as I still had the file page open in my browser ready to click Upload a new version of this file. Anyway, as you can see I've uploaded a dulled version with very subdued highlights. It looks like something that's been flushed out of the ISS to me. Only kidding, it looks okay I suppose. What do you think? nagualdesign 20:48, 10 December 2017 (UTC)

Darker isn't bad, since albedo predicted to be low. Can you increase the contrast so the shadowed area are more realistically VERY dark? Recall how dark the comet was that we visted 67P/Churyumov–Gerasimenko. You can also see my attempt to darken the shadows here. Tom Ruen (talk) 00:24, 11 December 2017 (UTC)

Done Any darker and it will be a silhouette. It reminds me of the Apollo 10 incident. nagualdesign 00:51, 11 December 2017 (UTC)

Okay by me. I'm probably most annoyed by the middle tapering, really would prefer the other 5:1 (e) "Whale" version, stretched out if needed. Tom Ruen (talk) 01:08, 11 December 2017 (UTC)

According to the article, the current best estimate is 6:1 and I don't think they'll be able to improve on that. I think the 'whale' one has the opposite problem; it looks a bit too fat in the middle, when most of the sources (AFAIK) describe it as somewhat cylindrical. It's the taper on the end that bothers me, making it look either 'pinched off' like a turd or aerodynamic like a rocket, but I guess if it was too regular it would look less like a rock. nagualdesign 01:18, 11 December 2017 (UTC)

Agreed. Can you do any Photoshop stretching to the middle so it doesn't taper? Tom Ruen (talk) 01:35, 11 December 2017 (UTC)

Of course I could, but like I said, if it was too regular it would look less like a rock, so I'd rather not. And as I mentioned a couple of weeks ago, each time we update the infobox many people might believe it to be based on new evidence. In this case the only thing that's changed is the colour, which isn't a bad thing. There aren't many image guidelines on Wikipedia but I think we ought to try to treat images the same as we treat prose, and altering a reliably sourced image in a way that isn't supported by references is tantamount to original research in my opinion. I hope you agree. nagualdesign 01:59, 11 December 2017 (UTC)

Sure, but looks like OR all the way down. No one really knows much of anything about what it looks like and any image is deceptive. Tom Ruen (talk) 10:27, 11 December 2017 (UTC)

The original image was published by the European Southern Observatory and the spectroscopy was published in the Astrophysical Journal. At worst this is WP:SYNTH, but as long as we limit ourselves to conscientious edits and refrain from imposing our own aesthetic preferences we're doing the best we can, which is what we should always do IMHO. I don't always follows the rules, I've even been known to break the law on occasion, but I do have my own standards of conduct that I almost never flout. I don't think that the image is at all deceptive. nagualdesign 19:34, 11 December 2017 (UTC)

I decided to put in the new image. At least being dark, it reflects its mysterious unknown appearance. Tom Ruen (talk) 17:08, 11 December 2017 (UTC)

Looks good. My gut tells me that the albedo's a little low, to be honest. The total observed brightness is a combination of the size/shape and the albedo, so I'd be interested to know what albedo they assumed in order to estimate the size. The variations in the observed light curve are probably due to irregularities in the object's shape or surface albedo, so it's either lumpy, elongated and relatively monochromatic (which seems to be the general consensus), or it's a little more patchy, or as I like to imagine (brace for OR..) it's much less elongated than they think, since spinning, tumbling rocks that fly near the Sun and survive tend to be more spherical, and therefore it would have to be much darker on one side. Obviously we can't just have a picture of a two-tone potato in the infobox though. nagualdesign 19:34, 11 December 2017 (UTC)

...I didn't realize until just now that we had a reference for the assumed albedo: It's 0.10 (by comparison, the Moon is 0.136). The reference also says, "A 6:1 axis ratio is extreme relative to most small solar system asteroids and suggests that albedo variations may additionally contribute to the variability," so two-toned idea isn't entirely OR after all. nagualdesign 14:45, 12 December 2017 (UTC)

A comet after all?

From Space.com: Interstellar Object 'Oumuamua Could Be a Comet in Disguise. Published 18 December 2017. The Nature article is here; it states: "An internal icy composition cannot therefore be ruled out by the lack of activity". In a few words, he thinks it may be a comet covered with tholins. BatteryIncluded (talk) 22:34, 18 December 2017 (UTC)

Wow. thanks for noticing. However, I was always of the conviction that you could determine the mass of an object from just looking at its trajectory. And when you know the mass and dimensions, density can easily be computed. Pretty straight forward. RhinoMind (talk) 00:40, 19 December 2017 (UTC)

The data was just obtained by several telescopes. I assume the interpretation and models of its mass and composition will keep flowing in the near future. BatteryIncluded (talk) 00:42, 19 December 2017 (UTC)

Um, no, determining the mass of a small body from its trajectory is exactly what you cannot do, in neither Newtonian gravitation, nor General Relativity. Only if the body influences another body gravitationally, e.g. an asteroid with a moon, can you determine its mass from motion, and then it's from the trajectory of the moon, the smaller body. -agr (talk) 00:54, 19 December 2017 (UTC)

@ArnoldReinhold: Well, the Sun bends this objects path, the bending is well-known and it is directly linked to the objects mass. We even know how the objects speed was influenced by the Suns gravity well. To me, that looks like a lot of data, certainly enough to estimate the objects mass? What is missing? RhinoMind (talk) 01:05, 19 December 2017 (UTC)

@RhinoMind: I was always of the conviction that you could determine the mass of an object from just looking at its trajectory. [...] Pretty straight forward. I'm not sure if you're joking or not but, just in case you're being serious, Galileo's Leaning Tower of Pisa experiment disproved Aristotle's theory of gravity over 400 years ago. Since then we've had Isaac Newton's law of universal gravitation, which was proved by Henry Cavendish over 200 years ago, and then a chap named Albert Einstein refined that with his special theory of relativity over 100 years ago. In short, if ʻOumuamua was a thousand times more massive (or even a million) it would still follow the same trajectory. Your conviction may be pretty straightforward, but you don't really understand what you're talking about. nagualdesign 11:01, 19 December 2017 (UTC)

Thanks for explaining it so well. I'm really impressed of your ability to regurgitate and at the same time leave out all logic argumentation. Now be off and annoy some other people. RhinoMind (talk) 17:43, 19 December 2017 (UTC)

You're welcome. Don't be annoyed though. Life's too short, and there are better (or worse) things to take umbrage with. nagualdesign 19:02, 19 December 2017 (UTC)

We do not know the dimensions, mass, or density of Oumuamua. Compared to the Sun, Oumuamua is a massless particle. -- Kheider (talk) 01:01, 19 December 2017 (UTC)

We have approximate estimates of its dimensions, enough to approximately estimate its density. All we are missing is the objects mass. RhinoMind (talk) 01:05, 19 December 2017 (UTC)

The dimensions are so poorly known as to make estimates very crude. Estimates of the density are based on the estimated proportions and that the object has to have enough internal strength to hold together as it rotates. (unsigned by User:Kheider)

Ok. Didn't knew internal strength was an issue for objects rotating in space. Anyway, I can't see why the objects mass cannot be calculated from the trajectory (including the speed profile). That was my main concern. RhinoMind (talk) 01:29, 19 December 2017 (UTC)

@Kheider: Hi again. Do you happen to know which article discuss and deduce the density from the objects "internal strength"? I can't find it. Thanks. RhinoMind (talk) 18:07, 19 December 2017 (UTC)

Its mass can be estimated only when it interacts closely with another celestial body or spacecraft (gravimetry, I think). BatteryIncluded (talk) 02:19, 19 December 2017 (UTC)

Hi. That applies if you want to measure a gravitational field, which is not the case here. I would say finding the mass of ʻOumuamua would just be down to basic Newtonian mechanics, in particular Newton's Second Law. But if it were that easy, someone would surely publish about it at some point I guess. RhinoMind (talk) 02:39, 19 December 2017 (UTC)

It's not a question of easy or hard, basic Newtonian mechanics says it's impossible. Newton's second law (F=ma) says an object's acceleration is the force applied divided by its mass. Newton's law of gravitation says the force on a small object is proportional to the object's mass times the mass of the larger body (the Sun, in this case), divided by the square of the distance between them. Put the two formulas together and it says that an object's acceleration, and hence its trajectory, does not depend on the objects mass at all, only the mass of the larger body and the distance. In General Relativity, this becomes the strong equivalence principle.--agr (talk) 12:18, 19 December 2017 (UTC)

Hi. Thanks for getting to grips with the theory. But this situation is not about a test body in a gravity field or a Free Fall. It is about how the Suns gravitational force affects an already moving body. How it bends the trajectory of a body with a certain mass, speed, momentum and kinetic energy. It seems counter-intuitive that the bend is completely independent of the body's mass. That it wouldn't even depend on its momentum, but only on its velocity. Weird. I'll better study this bit further. Thanks for the strong equivalence link, I think it might be useful. RhinoMind (talk) 18:02, 19 December 2017 (UTC)

@RhinoMind:But this situation is not about a test body in a gravity field or a Free Fall. It is about how the Suns gravitational force affects an already moving body. - That second sentence is exactly what a free fall is - see the first sentence of the free fall article: In Newtonian physics, free fall is any motion of a body where gravity is the only force acting upon it. 'Oumuamua is in free fall. --cyclopia ^speak! 19:15, 19 December 2017 (UTC)

Yes, yes. I'll probably get my head around this at some point.

Note to self: If you tried to push/pull a full-size truck moving at 20 km/h you would not see much bending of its trajectory, while if you applied the same amount of force to a cyclist also moving at 20 km/h, you would see a much larger effect. Problem is that the gravitational force scales up and down with the objects mass, so the effects on the trajectories would be the same in both examples, completely independent on the objects mass. I guess that small thought experiment explains the issue in a nutshell. RhinoMind (talk) 19:19, 19 December 2017 (UTC)

Here's the simplest explanation for this. F = ma. Gravitational force is F = GmM/r². So you have ma = GmM/r². The m cancels out on each side, leaving a = GM/r². This only depends on the mass of the Sun, not the mass of the orbiting body, so you cannot obtain any information on mass from trajectories in a 2 body system. Headbomb {t · c · p · b} 19:31, 19 December 2017 (UTC)

There is no need to limit this to a 2-body system. As long as the object of interest's mass is low enough that it cannot produce any measurable effect on the other bodies, it doesn't matter how many bodies there are. The acceleration of the small body is the vector sum of the accelerations produced by all of the other bodies and in no way depends on the small body's mass, per your analysis.--agr (talk) 20:32, 19 December 2017 (UTC)

(Edit conflict) A simple way to think about it is like this; The gravitational force on an object is proportional to its mass, but mass also defines resistance to inertia, so although something with 10 times the mass will be pulled with 10 times the force, it also offers 10 times the resistance. The practical upshot being that objects in a vacuum fall at the same rate, even a hammer and a feather. nagualdesign 19:40, 19 December 2017 (UTC)

Paper now at arxiv.org On above, I agree Kheider, don't see how its mass can be computed without any object orbiting it. Otherwise it all brightness with albedo and density estimates. On comet, all the paper says is "An internal icy composition cannot therefore be ruled out by the lack of activity." Tom Ruen (talk) 09:22, 19 December 2017 (UTC)

If ice is purely internal would that still count as a comet? Tlhslobus (talk) 12:44, 19 December 2017 (UTC)

Meanwhile maybe we should now be on the lookout for SETI people at Breakthrough Listen pointing out that such a lower-density interior would also be expected if it were an alien spaceship (perhaps especially one with a crew that was dead or hibernating, thus explaining the lack of signals from them) ? Tlhslobus (talk) 12:44, 19 December 2017 (UTC)

Certainly any assumptions can get you into trouble here. Since we don't know what its made of, at best we have surface estimates from reflected light, all models can be up to 100% wrong. Tom Ruen (talk) 13:36, 19 December 2017 (UTC)

Thanks, Tom, but one can't be 100% wrong if one just knows that on matters of faith and extraterrestials one is self-evidently more infallible than the Pope.

Tlhslobus (talk) 15:57, 19 December 2017 (UTC)

For classification purposes, it will only be called a comet if a Coma (cometary) is seen while outbound. -- Kheider (talk) 15:32, 19 December 2017 (UTC)

Thanks, Kheider, that presumably gets ever more unlikely as it moves away from the Sun.Tlhslobus (talk) 15:51, 19 December 2017 (UTC)

@Tlhslobus: To be specific, it is speculated that it might be an extinct comet. The current article on extinct comets calls these crusty comets dormant comets actually. Should we put that in our article here? RhinoMind (talk) 20:56, 19 December 2017 (UTC)

Damocloids are already mentioned in the Asteroidal nature section. Perhaps the term Tholins should be added to the article. -- Kheider (talk) 21:20, 19 December 2017 (UTC)

Ah yes. This small section contain it all actually. But do we know that ʻOumuamua's surface holds Tholins? RhinoMind (talk) 21:30, 19 December 2017 (UTC)

Tholins, yes: [3], [4], [5]. It is just a generic name for a complex mix of organics. -BatteryIncluded (talk)

Hi. Yeah these popular articles certainly mentions organic material. But the article that Tomruen links to above in this thread shows that the presence of organic material was only guessed at from the red colour of ʻOumuamua (here is the link again: [6]). It sounds a bit weak to me. But there might be other academic articles elaborating on it, I don't know. RhinoMind (talk) 04:24, 20 December 2017 (UTC)

While awaiting future articles that may not arrive, is there any reason why we shouldn't say something like "It is thought that its surface holds Tholins,[7] [8] [9] although this possibility is currently just inferred from its red colour[10]"? If nothing else this will help correct readers who may have been misled by the first 3 articles, which is what we at Wikipedia are supposed to do. Tlhslobus (talk) 09:45, 20 December 2017 (UTC)

I've now added a slightly changed version of that. If there are any problems they can always be fixed. Tlhslobus (talk) 10:58, 20 December 2017 (UTC)

I've also included a longish quote from the abstract, partly for the benefit of other editors, as it mentions slightly different dimensions from earlier estimates, as well as discussing ice. We might want to add a new composition section, but for now I'm just adding Composition to the section title. And I've now mentioned ice and cometary coma based on that paper.Tlhslobus (talk) 11:19, 20 December 2017 (UTC)

Not P-type

Bannister2017 specifically states, "As its albedo is unknown, we do not describe 1I/‘Oumuamua as consistent with Tholen (1984) P type."User-duck (talk) 03:52, 22 December 2017 (UTC)

But have other academic papers described it as such? I do not have an overview, but it is common for academic groups to disagree on subjects like these, especially when in the phase of interpreting and categorizing new data. Establishing categorizations and consensus "facts" often takes time and effort. RhinoMind (talk) 18:37, 23 December 2017 (UTC)

I am not researching, I am editing. The reference given for the "P-type" tidbits specifically states, "we do not describe 1I/‘Oumuamua as ... P type." Feel free to add it back when a reliable source is found.User-duck (talk) 20:36, 23 December 2017 (UTC)

System of origin?

Hello. Even though I have been editing this page I do not have a complete overview of this particular subject, so I would like to ask a question. We do not know from where ʻOumuamua originated, and there are several credible suggestions floating around. However, is an asteroid now bound to be originating from a planetary system? I mean, is some form of planet formation not required in order to produce an asteroid in the first place? Does any of the sources talk about this?

Reason: I have wiki-linked to stellar system in the leed, but should we not wiki-link to planetary system to be more specific? RhinoMind (talk) 22:16, 18 December 2017 (UTC)

I'm no expert, but the answer seems to be probably not, because asteroids are small bodies, the first of which will get built before planets, which are larger bodies built from smaller bodies.Tlhslobus (talk) 12:29, 19 December 2017 (UTC)

Hi. Yes true that asteroids are small bodies, but you don't build metal-rich rocky asteroids from scratch. It takes a very large body with a high density in the first place to compress the elements to such a high density. Maybe even geological activity to melt them into rocks. Then you smash it up somehow and get asteroidal fragments. Planetary bodies are precursors to metal-rich and rocky asteroids. RhinoMind (talk) 18:47, 19 December 2017 (UTC)

There is no clear evidence of its origin. I've heard the number 600,000 years for it to get near Vega's distance, but stars move a huge amount in that period of time, so Vega was no where near where it is now. So I imagine we'd need very accurate trajectories of the stars to have any hope, and if its origin was over 100 light years or more, then the chances go down even more. And there's no reason to not consider it's been traveling a billion years and many orbits around the galaxy before approaching our star. BUT I'm sure many people will try to refine stellar motion data for this case and more we'll find in the future. Tom Ruen (talk) 18:59, 19 December 2017 (UTC)

Sure, it seems almost an impossible task to exactly pinpoint which star system ejected this object. However, I was just talking about the nature of the parent system. I know we need to cite sources, but under the assumption it is a metal-rich asteroid I think we can safely say that it was created in a planetary system and not any random kind of stellar system. RhinoMind (talk) 20:49, 19 December 2017 (UTC)

Given the new uncertainties about the objects true nature as either an metal-rich rocky asteroid or perhaps an extinct comet (or an artificial spaceship), I don't think it is possible to say anything more precise other than "stellar system" at this point in time. RhinoMind (talk) 20:51, 19 December 2017 (UTC)

Agreed. Tom Ruen (talk) 21:01, 19 December 2017 (UTC)

Also agreed. Tlhslobus (talk) 09:28, 20 December 2017 (UTC)

Plus it may be a spaceship. AllGloryToTheHypnotoad (talk) 18:47, 27 December 2017 (UTC)

I have it from a good source it is actually a hologram, offered to us like we use laser beam to tease a cat. (e.g. Zoo hypothesis). Meow! BatteryIncluded (talk) 18:54, 27 December 2017 (UTC)

Animation

Test normal lines down to ecliptic plane
Full solar system	Inner solar system

I tried a ~20-month animation of 'Oumuamua's trajectory in the solar system, with 1 day steps close-in, and pauses on nearest date to Sun, Mercury, Venus and Earth. Interestingly Earth wins the best flyby. I zoom in during the closest passage, a bit jumpy there but otherwise seems pretty good. I suppose it would be interesting to add a computed distance and velocity over time. Tom Ruen (talk) 12:26, 16 December 2017 (UTC)

Excellent. Would be good to put in the article. Minor point : all the orbits draw over the white track of 'Oumuamua which makes it hard to see between which planet's orbits it passes down? and up? through the plane of the ecliptic. Could show the direction of the solar apex, maybe as an arrow from the sun ? Could perhaps have a different colour track for 'O prior to the first observation on Oct 19 ? Is there any way to allow viewer to pause/resume the animation ? - Rod57 (talk) 16:33, 16 December 2017 (UTC)

Agreed. I cleaned it up on a static image File:Oumuamua-solar_system_2018.png, but hard to automate at the moment since I just sort whole objects by distance, and don't use depth buffering. Tom Ruen (talk) 01:46, 17 December 2017 (UTC)

Looks very nice. Maybe add a point where it was first spotted from Earth? LouScheffer (talk) 16:40, 16 December 2017 (UTC)

IF the scale is correct, the existing lede image and body animation are incorrect. The actual angle between incoming and outgoing velocity vectors is ~66°. I would estimate the angle shown as being ~90°. There is no point of view that will make an angle appear larger.User-duck (talk) 17:42, 16 December 2017 (UTC)

P.S. How are the animations created? Shouldn't that be noted?User-duck (talk) 17:42, 16 December 2017 (UTC)

I added more information to the source data. I should add an option to make the view orthogonal to the motion of an given object, but I'm just selecting by visually rotating with a mouse. I measured the animation at wide angle as 68°. I also checked this image File:Oumuamua-solar_system_2018.png, and I did better there, measured on the screen about 66°. Tom Ruen (talk) 01:40, 17 December 2017 (UTC)

@User-duck: There is no point of view that will make an angle appear larger Of course there is. If you lay an equilateral triangle on a table and look at it from above the angles all appear to be 60°, but if you look at it from a shallow angle two of the corners will appear less than 60° while the third will appear greater. If you duck down (see what I did there?) so your eyes are almost level with the table, one of the corners will appear to be almost 180°. Science, y'all! ^link nagualdesign 12:06, 17 December 2017 (UTC)

I realized my mistake a few days ago. My point of views were relatively close to the ecliptic plane. I realize now realize if my POV was perpendicular to ecliptic the trajectory would be almost a straight line.User-duck (talk) 16:15, 20 December 2017 (UTC)

I feel the images should show the magnitude of the change of direction and how close the perihelion was to the sun. It is tough to show the relative speed, animation should be good for this.User-duck (talk) 16:15, 20 December 2017 (UTC)

"File:Comet 20171025-16 gif.gif" seems to show the speed difference, it was only about 1 to 3.User-duck (talk) 16:15, 20 December 2017 (UTC)

I infer from "File:Oumuamua orbit at perihelion.png" that inbound ʻOumuamua crossed the ecliptic plane inside the Mercury orbit. Is this correct?User-duck (talk) 16:15, 20 December 2017 (UTC)

Yes. Tom Ruen (talk) 17:47, 20 December 2017 (UTC)

I tested some ecliptic plane normal lines to help show how far Oumuamua is off the ecliptic plane. I think it is helpful for visual clarity (You can better see the leaving angle is closer to ecliptic than approach), although unsure if it would help an animation. Tom Ruen (talk) 11:37, 17 December 2017 (UTC)

Here's a second animation, File:Oumuamua_trajectory_animation2.gif, with a vertical line to show distance from the ecliptic plane. Its 12Meg, so probably can't be rescaled by Wikipedia. Tom Ruen (talk) 12:48, 17 December 2017 (UTC)

"Interestingly Earth wins the best flyby"- Obvious selection effect; with interstellar visitors just beginning to come into practical observation range, in order to be the first one seen you're likely going to need to make a specially nice Earth flyby. This could potentially be mentioned in the article somewhere, in connection with the general issue of how the observation of 'Oumuamua relates to estimating the population of similar objects. If I'm not making some silly mistake then the solar system should be constantly infested with interstellar visitors and probably the only thing remarkable about 'Oumuamua is its having won the first-seen lottery. 68.196.180.180 (talk) 13:14, 31 December 2017 (UTC)

Flat disk or cigar?

Is there any data that says weather its flat like a quarter or long likea cigar? The origional data suggested 13.68 variation in brightness. Spectral variation suggests uniform substance with iridencence (harmonic variability bands) But nothing says 'not disk' or 'not cigar' So as everyone been watching the movie 'space truckers' or what? Pure thoughts.. - 72.94.231.164, 13:33, January 7, 2018

I don't know how the light curve of a tumbling disk would look compared to a tumbling 'cigar'. My only guess is that disks are less likely to tumble off axis. Tom Ruen (talk) 00:07, 8 January 2018 (UTC)

As an aside, I've been thinking about that light curve recently. I'd previously stated that it could be due to ʻOumuamua being two-tone but I've since realized that, if it were, the light curve would be sinusoidal. The observed light curve is more like a rectified sinewave (with a non-zero minimum amplitude), which definitely suggests an irregular object with a cross-sectional area that differs drastically from one aspect to another. Whether that means a tumbling cigar or a tumbling disk I have no idea. Are there even any known disk-shaped objects? My understanding is that most smaller astronomical bodies tend to be (roughly speaking) prolate spheroids, while much larger ones like planets tend to be oblate spheroids. nagualdesign 00:53, 8 January 2018 (UTC)

This is pure guesswork but I'd expect that a tumbling disk would have a much sharper spike in brightness when the flat(ish) faces are at a particular angle to the Sun, much like the flickering of a tossed coin as it moves through the air – it winks. nagualdesign 00:56, 8 January 2018 (UTC)

Agreed, curve doesn't fit albedo variations of a rotating sphere, and agreed flatish surfaces might produce brightness spikes. A double-spiking brightness (each slightly different) could suggest a two-sided object. Tom Ruen (talk) 04:48, 8 January 2018 (UTC)

I created this animation as I thought the light curve on its own might be a little opaque to a lot of readers. It certainly took me a while to get my head around it. Hopefully by seeing this people will understand why astronomers believe ʻOumuamua to be cigar-shaped. I'd add it to the article myself but, since this is an original work, there may be some opposition and frankly I haven't got the energy. I'll leave the finer details to you, Tom, if you don't mind. nagualdesign 08:59, 8 January 2018 (UTC)

Nice! I had thought of doing the same thing. I put it up as-is. Tom Ruen (talk) 10:12, 8 January 2018 (UTC)

Looks good.

nagualdesign 12:38, 8 January 2018 (UTC)

Interesting tidbit about 10,000 others

I feel this tidbit should be worked into the article:

"Astronomers ... and estimate it could be one of 10,000 others lurking undetected in our cosmic neighbourhood"

It is currently buried in a reference. I believe I have seen this info in several of the sources already cited. I do not know if it warrants a new section or just a mention in the lead (or Nomenclature).User-duck (talk) 22:48, 24 December 2017 (UTC)

I feel like that is such a random number pulled out of hat that it's not worth mentioning. We have a sample size of one at the moment. — Huntster (t @ c) 02:21, 25 December 2017 (UTC)

Not worth to mention such guess, especially in the leade. BatteryIncluded (talk) 04:35, 25 December 2017 (UTC)

Same as the two commenters above. I think it is a figure pulled from one of the papers talking about the local cosmic density of interstellar asteroids. I can't exactly remember the paper, but recalls to have read about estimates about this. If we are to put something up about this issue on Wikipedia, I think we should use the academic paper, as it hold more info than just a number. I also believe, that the issue is better suited for the Interstellar object article, than this one, mostly because it is general knowledge and not tied to ʻOumuamua in particular. RhinoMind (talk) 20:11, 27 December 2017 (UTC)

It's an interesting question, but if someone is making estimates we need details, like how big is our "cosmic neighborhood"? It is heliosphere or the Oort cloud or all space closer to the sun than any other star? And how many of those are on trajectories that will end up inside the orbit of Mercury? I'd bet the numbers go way down if you add a criterion like that. And I presume it's referring to objects of the size of Oumuamua or larger, so say ~100 meter diameter? Tom Ruen (talk) 20:51, 27 December 2017 (UTC)

This article, Our Cosmic Neighborhood seems to suggest our "cosmic neighborhood" includes neighboring star systems! Tom Ruen (talk) 20:54, 27 December 2017 (UTC)

"cosmic neighbourhood" is not a fixed volume of space, but is changing according to the subject discussed. On galactic scales, the entire Virgo Cluster is our local cosmic neighbourhood. Anyway. All this back and forth comes down to finding the exact academic paper that discuss the issue raised by User-duck. When we have this, everything will fall into place and we don't have to guess or interpret anything. The paper is in the References section already, but I can't recall the name and I don't have much time to track right now. Maybe someone else is excited enough to look for it? RhinoMind (talk) 23:41, 27 December 2017 (UTC)

I think it would fall into WP:CRYSTALBALL if we start quoting guestimates on the next interstellar visitor. Astronomers just don't know! -BatteryIncluded (talk) 00:35, 28 December 2017 (UTC)

The source of the 10,000 number is David Jewitt "The steady-state population of similar, 100 m scale interstellar objects inside the orbit of Neptune is ~10,000, each with a residence time ~10 yr." You can find it here http://www2.ess.ucla.edu/~jewitt/2017U1.html and in this paper https://arxiv.org/abs/1711.05687. He also mentions it in a talk he gave at Griffith Observatory https://www.youtube.com/watch?v=pLeyBqw6gWs EighteenFiftyNine (talk) 10:47, 27 January 2018 (UTC)

ʻOumuamua's tumble hints at violent past

I spotted this article and thought it might be worth mentioning: 'Oumuamua: 'space cigar's' tumble hints at violent past nagualdesign 07:57, 12 February 2018 (UTC)

Already referenced in the body of the article. BatteryIncluded (talk) 14:38, 12 February 2018 (UTC)

Scout computer program

Does the name ʻOumuamua have any connection to the computer program named Scout?

First deployed in 2016, "By monitoring observations of newly reported space objects, a computer program called Scout can quickly identify potentially dangerous asteroids, then automatically call for follow-ups to calculate a more precise path for these bodies" [11] --RoyGoldsmith (talk) 23:07, 19 February 2018 (UTC)

Scout is the Sentry Risk Table's little brother. Scout is useful for newly discovered objects where a potential impact might be imminent, while Sentry is intended more for threats years into the future. I do not see why the program Scout would have any significance to ʻOumuamua. -- Kheider (talk) 01:47, 20 February 2018 (UTC)

Heliocentric eccentricity

I made a graph of eccentricity as exported from JPL Horizons, and I'm surprised it is not only not stable but unstable, variations (from Jupiter) are growing with time. Is this "real"?! I can imagine how this might be possible, but still seems unreasonable. ... Okay, I updated, adding barycentric in red, and that's what I'd expect. @Kheider:, what do you think? Tom Ruen (talk) 05:19, 12 March 2018 (UTC)

As eccentricity = (a-q)/a, when the perihelion point is further out, the corresponding eccentricity will be greater. When "EC= 1.3", perihelion (QA) will be around 0.4 AU. When "EC= 1.06", perihelion will be around 0.08 AU. But this graph is a good example of why a random heliocentric epoch is not as stable as a barycentric solution. -- Kheider (talk) 14:04, 12 March 2018 (UTC)

Space missions section

ʻOumuamua is gone and is unreachable, so I think that we should modify the Space mission section to mention only the proposals for future extra-solar objects. (This is one of the latest studies: THE FEASIBILITY AND BENEFITS OF IN SITU EXPLORATION OF ‘OUMUAMUA-LIKE OBJECTS, and: [12].)

Another issue is the statement that interception "is impossible". A flyby —or even better and impactor— would give a wealth of information, specially if it splits in 2 just before impact, one being a relay transmitter. This study states that given trajectories and velocity, and using the Falcon Heavy (chemical propulsion): "It is clear that, given sufficient warning, it would not have been energetically difficult to intercept ‘Oumuamua." My physics background is not that great to translate the details of this study into Wikipedia, so I'll just leave it on your desk. Cheers, BatteryIncluded (talk) 17:04, 18 April 2018 (UTC)

arXiv:1801.02658v2 [astro-ph.EP] 'Oumuamua is a fragment of a white-dwarf-star tidal disruption event ! 87.152.14.234 (talk) 23:41, 30 April 2018 (UTC) in the middle of the article is the description: According to one hypothesis, ʻOumuamua could be a fragment from a tidally disrupted planet.[50], which I think comes close, but this is Bingo: arXiv:1801.02658v2 [astro-ph.EP] Roman R. Ravikov Jan,16th,2018 draft version: 1I/2017 ’OUMUAMUA-LIKE INTERSTELLAR ASTEROIDS AS POSSIBLE MESSENGERS FROM THE DEAD STARS , it explains: 'Oumuamua is a fragment of a white-dwarf-star tidal-disruption event. This easily explains its extreme elongation (6:1 up to 10:1 ) and its "refractory", metallic composition. in exterme it could be the disrupted molten nickel-iron core of a planet or planetoid! This scenario is quite more real than the "alien-spaceship" hypothesis. A origin from a WD-TDE makes it a very rare ISO! The estimates of "abundant" inter-stellar-objects are based on frequency of "astray" asteroids or "dusty-snowball"-comets of interstellar origin; but 'Oumuamua is special. This part of this Wiki should be expanded! (more professional, than I could do) ^[1] 87.152.14.234 (talk) 00:12, 1 May 2018 (UTC)

'Oumuamua is no alien-spaceship, SETI results still negative. I am thinking of the possible chances of a (Star-Trek!!! Fusion-Power-) spaceship Enterprise_2.0 , potentially intercepting and tugging 'Oumuamua back to the solar system? (for its precious metals?) If NASA would send a New-Horizons probe to exactly locate 'Oumuamua's trajectory in the outer expanses of the solar system, it wouldn't get lost and in several hundred years it could be targeted by advanced spaceships. 87.152.12.52 (talk) 00:51, 1 May 2018 (UTC)

References

^ arXiv:1801.02658v2 [astro-ph.EP]

[1] rXiv:1801.02658v2 [astro-ph.EP]

[1]