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Unusual Visitor: A Deeper Look at ‘Oumuamua

When I first wrote about the interstellar interloper now called ‘Oumuamua, I made reference to Arthur C. Clarke’s Rendezvous with Rama because of the delightful symmetry between the novel and the object, though noting that ‘we’re unlikely to find that A/2017 U1 is as intriguing as Clarke’s mysterious starship bound for the Magellanics’ (see An Interstellar Visitor?). Still, an interstellar object entering the Solar System only to go careening back out of it could not help but recall Clarke, whose ‘asteroid’ 31/439 wound up being artificial.

Then came the paper from Karen Meech (University of Hawaii Institute for Astronomy, where the object was first detected with the Pan-STARRS1 telescope). Drawing on data from telescopes around the world, Meech’s team has been able to characterize our first nearby object from another stellar system, with equally delightful results. For it turns out that ‘Oumuamua (pronounced oh MOO-uh MOO-uh) has an unusual axis ratio, being about ten times longer than it is wide. Jim Benford couldn’t resist suggesting I show a cover from Rendezvous with Rama depicting just such an axis ratio, and I agreed wholeheartedly.

Any science fiction fan familiar with Clarke (and are there any who aren’t?) will have fun with the similarities, but how much do we actually know about ‘Oumuamua? Meech’s team based its conclusions on the object’s shape on the fact that its brightness changed so dramatically as it rotated (spinning on its axis every 7.3 hours). Lance Benner, who specializes in radar imaging of near-Earth and main-belt asteroids at JPL, calls the axis ratio here ‘truly extraordinary.’ We know of no Solar System objects elongated more than 3 times longer than they are wide.

Nothing in our Solar System, in other words, quite matches an object shaped like this. Of course, it might also look like the image below, courtesy of the European Southern Observatory.

Image: This artist’s impression shows the first detected interstellar asteroid: `Oumuamua. This unique object was discovered on October 19, 2017 by the Pan-STARRS 1 telescope in Hawai`i. Subsequent observations from Gemini, ESO’s Very Large Telescope in Chile, CFHT, UKIRT, and other observatories around the world show that it was on a path which must have been travelling through interstellar space for millions of years before its chance encounter with our star system. `Oumuamua seems to be a dark red highly-elongated metallic or rocky object, about 400 meters long, and is unlike anything normally found in the Solar System. Credit: ESO/M. Kornmesser.

On the other hand, the object’s light curve, as examined through data from the Canada-France-Hawaii Telescope (CFHT), can show us rotation and likely axis ratio, but the overall observations — from the United Kingdom Infrared Telescope (UKIRT), the Keck Telescope on Mauna Kea, the Gemini South telescope, and the European Southern Observatory (ESO) Very Large Telescope (VLT) in Chile as well as CHFT — show similarities with local objects as well as differences. Here’s Karen Meech on those findings:

“While study of `Oumuamua’s colors shows that this body shares characteristics with both Kuiper Belt objects and organic-rich comets and trojan asteroids, its hyperbolic orbit says it comes from far beyond.”

The object’s dark red color is similar to Kuiper Belt objects, and the researchers believe it is dense and rocky or with high metal content, an asteroid that, according to this ESO news release, lacks significant amounts of water or ice, and one whose surface darkening and reddening is the result of millions of years of irradiation. Current length estimates are in the range of 400 meters.

So while its composition is similar to objects in our Solar System, its shape is unique and so, of course, is its origin. Observations of the object had to be quickly compiled, for while it was only 85 times the Earth-Moon distance away when discovery was announced earlier this month, it is moving away rapidly. It was clear to the discoverers that they had little time to gather data on this enigmatic visitor. Thus Gemini director Laura Ferrarese, who applied Gemini South’s resources to the study for Meech’s group: “Needless to say, we dropped everything so we could quickly point the Gemini telescopes at this object immediately after its discovery.”

Both Hubble and Spitzer are also tracking the object the week of November 20, according to JPL. And here’s another science fictional bit: Preliminary orbital calculations show `Oumuamua came from the approximate direction of Vega, in the constellation Lyra. That just might recall Carl Sagan’s novel Contact, where a SETI signal containing data is found to be coming from Vega, 26 light years away, leading to the construction of a most unusual device.

But there the similarities end: Our object is simply traveling too slow to have been sent from Vega, which would not have been nearby when `Oumuamua was there 300,000 years ago.

Image: This composite was produced by combining 192 images obtained through three visible and two near-infrared filters totaling 1.6 hours of integration on October 27 at the Gemini South telescope. Processing removes the background stars. The field of view represents a patch of sky 5,000 km on a side at the distance of `Oumuamua. Visible colors for the image were assigned to each filter as follows:
g (398-552 nm) = blue
r (562-692 nm) = green
i (706-850 nm) = yellow
z (830-925 nm) = orange
Y (970-1070 nm) = red
While assigning visible colors to filtered images is somewhat subjective, the resulting color of `Oumuamua in optical light is similar to the hue of some of the moons of outer planets in our Solar System, and possibly indicates a similar composition (a combination of minerals, carbon, iron, and organic compounds). Color composite produced by Travis Rector, University of Alaska Anchorage, using Gemini South GMOS data obtained and processed by Meech et. al. Credit: Gemini Observatory/AURA/NSF

Are we going to find more such visitors? Ejected comets and asteroids, forced into the deep through interactions with larger planets, may be relatively common. In fact, Robert Jedicke, who is part of the team working with Meech, estimates that a similar object, of similar size, is out there between the Earth and the Sun at any given time, up to perhaps 10 every year. If so, it will be surveys like Pan-STARRS and the future Large Synoptic Survey Telescope (LSST) that begin to compile statistics on the frequency of visitors like `Oumuamua.

`Oumuamua is now traveling at 38.3 kilometers per second relative to the Sun, about 200 million kilometers from Earth, and will pass the orbit of Jupiter in May of 2018, headed in the general direction of the constellation Pegasus. We should be able to continue to refine its trajectory as it leaves the Solar System through mid-December, when it becomes too faint to detect.

I am not saying this is going to happen, but wouldn’t it be fascinating if we learned it was headed toward another nearby star…

The paper is Meech et al., “A brief visit from a red and extremely elongated interstellar asteroid,” published online by Nature 20 November 2017 (abstract).

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{ 59 comments… add one }
  • Antonio November 21, 2017, 11:08

    They should have named it Rama!

  • ljk November 21, 2017, 11:16

    According to this press release, which I link to next and quote from:

    http://ifa.hawaii.edu/info/press-releases/Oumuamua/

    Astronomers estimate that an interstellar asteroid similar to `Oumuamua passes inside the orbit of Earth several times a year, but they are faint and hard to spot, so they have been missed up until now. It is only recently that survey telescopes, such as Pan-STARRS, are powerful enough to have a chance to discover them.

    “Our successful follow-up observations are a model for the future — especially when the next major survey telescope, LSST, comes on line,” added Meech.

    So is ‘Oumuamua truly rare, or just rare to humanity because we have not been able to detect them before? Do we have enough data to calculate the odds of how often a planetoid or comet from another star system may randomly pass through ours? How do we know how unusual is the makeup of this visitor if we have nothing else to compare it to?

    • hiro November 21, 2017, 20:19

      Well, the probability of an interstellar object’s trajectory passing “close” to the Sun & Earth + probability of its unusual shape. The last missing piece is a neon sign on the surface showing the middle finger.

  • DJ Kaplan November 21, 2017, 13:20

    It’s really weird and maybe prescient that the Hawaiian name `Oumuamua is supposed to mean “messenger” or “scout”. I’m tempted to add “Bracewell probe”.

    What’s the chance of a natural asteroid achieving this shape?

  • Frank Smith November 21, 2017, 13:28

    That axis ratio is somewhat spooky…

    • Mike November 22, 2017, 2:14

      I found it to be astonishing. If the dimensions can be verified then it’s a real puzzle.

  • Michael November 21, 2017, 13:46

    That sort of object could give ample protection to organics or life on the long journey but at that velocity impacts would be very violent.

  • Steven Ward November 21, 2017, 13:47

    I read about it’s unusual shape last night and was hoping Paul was going to post about it. I can’t wait to hear the comments!
    So it was rotating around it’s axis. Was it not tumbling? This is awesome! How would a natural process produce a long shape like this? Maybe the Allen Array will take some interest and take a look at it. What if it started slowing down? Wow, the questions I have!

    • Matt McIrvin November 23, 2017, 11:28

      I think it is tumbling, since the aspect ratio was deduced from the light curve.

      • Steven Ward November 24, 2017, 1:37

        Thanks, that makes since. If it is tumbling, that to me, would suggest that it is a natural object. I would think that a controlled object would maintain a constant position relative to its flight path as our space vehicles do. Maybe I could see if the tumble has a centrifugal purpose.

        • WildCol December 11, 2017, 19:47

          Actually, a tumbling (or ‘rotating around a non-principal axis’) would be a very sensible thing for an unmanned alien probe. Say you want to pack a lot of different sorts of sensors into it, rather than having six of each type (to cover each direction), you just tumble the probe so that over the 7 hour rotation period, each sensor will be able to observe the vicinity.

  • DJ Kaplan November 21, 2017, 14:47

    What are the constraints on its mass?

    • DJ Kaplan November 21, 2017, 16:21

      I calculate it would be 487,782,000-541,980,000 kg or 537,687-597,430 tons, depending on estimated size and assuming some marterial like basalt.

  • Alex Tolley November 21, 2017, 14:50

    This object has a much higher length to diameter ratio than either Rama or an O’Neill Island 3 cylinder. It is however, much lower than that of “The Way” in Greg Bear’s trilogy (Eon, Eternity, Legacy).

    Our first extra-solar visitor and it doesn’t look just like a normal object from its physical dimensions. I hope the calculation is correct that we could discover a lot more of these with better scopes. This makes a possible probe rendezvous far more likely in future.

    Is it possible these are the result of Oort cloud perturbations as stars pass close by? Could analysis of their compositions indicate previous stellar encounters?

    • Mike Synnott December 12, 2017, 8:27

      Wasn’t the object in the Greg Bear novels called Thistledown by its creators; or the Stone or the Potato, by the US and Soviets, respectively? I think “The Way” was the tunnel/ribbon boring through spacetime from the end of the craft itself.

  • Jack William Bell November 21, 2017, 15:02

    “Our object is simply traveling too slow to have been sent from Vega, which would not have been nearby when `Oumuamua was there 300,000 years ago.”

    The obvious question to ask then, is what stars were in that location 300,000 years ago. Or, more accurately, what stars were in it’s path at the time it passed any point along its current path. Could it have started its journey nearer or further than Vega? Alternatively could it be a probe ‘banking’ along a sequence of stars?

    For the second question, also it is important to know if the object changed from its expected path in any way after its closest approach to the Sun?

  • Tom Mazanec November 21, 2017, 15:25

    Is the current path towards any other star?

    • Paul Gilster November 21, 2017, 16:15

      I don’t think we have a good enough trajectory to know. But the object should be viewable until mid-December, so perhaps we can tighten up the parameters and get some idea.

  • Eric November 21, 2017, 15:57

    Can Arecibo look at it? Or is it still out of commission?

    • DJ Kaplan November 21, 2017, 16:41
      • ljk November 21, 2017, 18:35

        Arecibo may not be torn down any time soon, but it is still not working as an astronomical observatory two months after Hurricane Maria came through Puerto Rico. Perhaps China’s FAST radio observatory can do the job?

  • Michael November 21, 2017, 16:11

    Might be a solidified crust shard perhaps a violent interaction in its home system that lead to its ejection or just maybe,

    http://media.moddb.com/images/mods/1/7/6925/Imperial_I-Class_HD.jpg

  • Geoffrey Hillend November 21, 2017, 16:56

    Elongated or cylindrical asteroids are theorized to have been formed during accretion by two smaller asteroids that are close together revolving on a center of mass.

    • DJ Kaplan November 21, 2017, 17:38

      Thank you. Would they still stick together if the combined body was tumbling at a period of 8 hours? I’m not even sure a column of solid rock would have enough tensile strength to stay in one piece.

      • Harry R Ray November 22, 2017, 10:31

        If the object were predominantly metal, some of which was FUSED by melting and re-solidifing as a result of some violent event during its creation, I would say, probably yes. However, assuming that astronomers’ calculations that its albedo is extremely low, even the above scenario would not prevent it from being broken to pieces during its closest passage to the Sun, where its surface temperature would reach well over 1,000 degrees farenheit, and tidal stresses due to its elongated shape would reach MAXIMUM(if any reader can compute this tidal stress, please do so and post the results HERE).

    • Michael November 21, 2017, 17:46

      That ratio would be closer to 2:1, 10:1 is unusual, maybe part of a lava field over laying softer regolith which was then ejected during a collision.

  • FrankH November 21, 2017, 18:27

    Is it rotating along it’s long axis or short axis (which would be even odder).

    If this is an artificial object, this is the best look we’ll ever get of it – which sadly points out our extremely primitive technology.

    I think it’s clear that it’s a Culture ROU – maybe “Your Planet lacks Gravitas”

    • hiro November 21, 2017, 20:15

      The direct descendant of the GCU Arbitrary, “My Name is Red” is more likely and of course it also failed to request Mr. David Bowie’s Space Oddity.

      • Harry R Ray November 22, 2017, 10:34

        But it now knows that the humpback whales are still here. WHEW!!!!!

  • ljk November 21, 2017, 18:40

    While it may not be quite as elongated as our visitor from beyond, 1620 Geographos is definitely not a sphere:

    https://en.wikipedia.org/wiki/1620_Geographos

    Radar images here:

    https://echo.jpl.nasa.gov/asteroids/1620_Geographos/pics/pretty01/index.html

    Itokawa may have been even less elongated, but it was visited by the Japanese space probe Hayabusa:

    http://global.jaxa.jp/article/special/hayabusa_sp3/index_e.html

  • Wojciech J November 21, 2017, 19:00

    This reminds me of the short story “Pirx’s Tale” by Stanislaw Lem from ”Tales of Pirx the Pilot” ;)

    • Matt McIrvin November 23, 2017, 11:30

      That was my first thought as well! I think Pirx’s object was toroidal.

  • Bill Swallow November 21, 2017, 19:41

    This is such a fascinating event! And it’s so disappointing that there’s no way at all for us to really study it. By the time we got done arguing about whether we could or should, it would be much too late. Not to mention the years it would take to design and build a probe. Which prompted a thought…

    Why would it not be a good idea to maintain a few ‘off-the-rack’ probe payloads in a state of readiness, mothballed for quick response, to be able to respond nearly instantly to ‘target-of-opportunity’ missions like this?

    I know the space science types love to tailor-make one-off probes that are optimized for whatever they’re being sent to look at, but as I said, that lead time ensures that we could never, ever seize the moment when an unexpected gift like this comes along.

    Wouldn’t it be nice to have a few general-purpose probes on the shelf that could be put atop a Falcon Heavy or similar rapid response launcher and sent on their way within a few days or a week of detecting something interesting?

    Better a less-than-optimal mission than no mission at all.

    Maybe a production run of a half-dozen standardized payloads could even bring the price down a little.

    We could even maintain two varieties of standardized probes. Really stripped down, lightweight probes for high speed and longer range, and a bigger, heavier variant with more instrumentation.

    “Ready a Class-One Probe for a flyby of the object! Make it so!”

    Of course, the problem is, who would be willing to underwrite such a project? It’s an investment, and one with a possibility of taking years or even decades to pay off, if ever, and that’s always a difficult sell.

    Elon Musk might be able to do this, but would he? This isn’t exactly along a direct line to his goal of making man a multi-planet species, and it would tie up some amount of capital he could probably use elsewhere.

    The space science types would seem to be the logical constituency, but they have so much trouble funding missions, I sadly don’t see them supporting an effort that might never generate any data, or any papers.

    We seem to be doing tolerably well these days with rapid-readiness launchers. To make this happen would need funding and support for probe payload design, construction, testing, storage, and maintenance.

    But if we *don’t* do this, we will never, ever be able to take advantage of opportunities like this, and who knows what we’ll miss?

    • Curious November 21, 2017, 22:05

      You would want it ready mounted on an all solid rocket, probably based on a current ICBM. That way you would be ready to launch almost immediately which you’d need given how short the reaction time to this thing was.

    • Malcolm Davis November 22, 2017, 0:25

      You and I had similar thoughts (see my post below), and I’m sure a lot of people are thinking the same thing. Why launch from Earth if they could be space-based?

      • Curious November 23, 2017, 0:58

        Space based might have velocity/intercept trajectory advantage (I am not a GNC guy) and/or enabling a heavier sensorhead – assuming you could put a bigger one up with a large liquid ELV. But I think some major disadvantages of space based would more than offset that and include: keeping the rocket and sensorhead ready in space environment for long waiting periods, difficulty in upgrading the sensorhead when desired, initial cost, cost to keep it ready while waiting. So I think Earth basing would be the best choice and certainly in near term when you are trying to get even just a basic sensorhead up there.

        I would add that such a sensorhead could be developed to be specifically non-ITAR and compatible with large range of launch loads that it could therefore be offered (perhaps just the design if funds are tight) to other Space Agencies with suitable launchers in case they want to join in this quest.

  • Patrick Underwood November 21, 2017, 19:50

    We only know its velocity after detection. If it is a thing-that-must-not-be-named, it might have decelerated from relativistic sometime prior to detection. Maybe look through records for a slight rise in, say, high energy particles in the weeks or months preceding? Exhaust, you know.

    Hey, just sayin.

  • Malcolm Davis November 21, 2017, 19:51

    This event should inspire us to develop the means to have a series of space probes, based in orbit, that can be quickly tasked to respond to unexpected events like Oumuamua. If we’d had a probe ready to intercept it, and get a closer look, and do so relatively quickly, that would be a highly useful capability.

    Let’s say that in the 2020s we build the Deep Space Gateway at one of the Lagrange Points. One of the roles it could function would be a support base for a small number of purpose-designed space probes designed to give us the means to respond to unexpected developments like this. The probes would have to have a common design, and have fast propulsion so they could reach a destination as quickly as possible. Solar-electric or nuclear-electric maybe. They would have common instrumentation to survey a newly discovered object. They would be designed to be based in space, and available ‘on-call’ when needed, so they’d need to have a sustainable power source. If based at the Gateway (I chose that on the assumption ISS won’t stay in orbit forever), they should be proximate so they can be serviced and upgraded when needed.

    We could even use CubeSat or Small Satellite technology to keep the cost down, allowing us more capability for money invested, or if we deploy one, we can quickly replace it. The main challenge is getting sufficiently high thrust so that it can close with and intercept an object as soon as possible, but have sufficient thrust to match velocity to do useful science. So we’re not talking chemical rockets.

    With Oumuamua we are stuck with distant observations. In the future when this happens again, we should have a spacecraft ready and waiting to give us a close up look.

  • andy November 21, 2017, 20:32

    Another attempt to determine a system of origin: Dybczyński & Królikowska “On the dynamical history of the recently discovered interstellar object A/2017 U1 – where does it come from?
    Candidates within 30 pc include UCAC4 535-065571, Delta Capricorni and Gliese 876 (host to four planets but so far no detection of a debris disc).

    Do a quick reconnaissance and get out of the way before the Earthlings get too good a look? Something like a Firefall perhaps? Or maybe we missed Firefall entirely, and this is the Burns-Caulfield decoy, designed to distract our attention while Rorschach bides its time somewhere in the outer darkness, preparing an attack in retaliation against the METI spam we’ve been broadcasting to various systems. :-P

  • NMM1AFan November 21, 2017, 21:46

    Definitely the most interesting astronomy story of the year!

    • AG December 12, 2017, 11:05

      Totally agree!

  • Mike November 22, 2017, 2:05

    I don’t think we are going to be able to learn much more about this object. If the dimensions are accurate than it is an anomaly. In a way I would compare it to the Wow! signal. No one knows precisely what that was either. People will be discussing and debating Oumuamua for decades as they have for the Wow!.

    However when the LSST goes into operation in a few years and if objects with interstellar speeds and trajectories are routinely detected that would mean they are as common as David Jewett proposes and good evidence they are only ejected asteroids after all.

    That might not explain the anomalous dimensions.

  • Ron S. November 22, 2017, 11:04

    Someone’s going to post this eventually so it might as well be me. Enjoy.
    https://xkcd.com/1919/

  • Andrew Palfreyman November 22, 2017, 13:04

    Having a beamer on standby would have been a real boon. Sending a StarChip swarm towards it at 0.2 c would hopefully produce impacts which could be spectroscopically analysed by others in the swarm and radio’d back, a la StarShot. We could make a start on building the beamer array right now, slowly filling it out over time.

    • Michael November 24, 2017, 4:20

      The laser itself could probe the structure and composition of the object and look at the isotopes which could be compared to nearby stars light spectrums.

  • Stephen W November 23, 2017, 0:38

    There is still time for it to turn on its Orion engines if it wants to enter a solar orbit.

    Most of the stars visible in the sky like Vega are large bright with lots of UV and x rays. The place to look for ETI would be all the less noticeable yellow and orange stars. If they are not really close most go unnoticed unless a telescope is pointed at them.

  • AG December 12, 2017, 11:00

    I wonder where this object is in reference to the Voyager probes. I read elsewhere that it is interesting it dipped into the habitable zone. So what if there are no signals? If it was trying to be low key it would hold off transmitting until well out into interstellar space right?

  • ALH December 12, 2017, 15:12

    Has its density been estimated? If so, how was this done and what were the results?

  • Martin December 30, 2017, 23:19

    If Oumuamua is artificial and there was some design behind its convoluted and unnaturally elongated shape, odd dust and ice-free composition and otherwise very fortuitous flyby of our odd little planet that has been emitting artificial radio signals and large amounts of visible light from its dark side for about 100 years, then the obvious origin might still be Vega. At 25 light years away, Vega is well within Earth’s growing radio/light bubble which is now about 100 light years in radius, and a civilisation there with much greater observation skills than ours might have been monitoring our output for decades (and hopefully enjoying David Bowie and not taking any drastic decisions based on our generally warlike nature, contempt for other species and fast advancing space technology). But, although travelling fast by solar system standards, Oumuamua is travelling far too slowly to have been sent from anywhere within that bubble in response to our signs of intelligent life. Unless, of course, said nearby advanced civilisation had also mastered the faster-than-light interstellar travel esential to so much of our sci-fi. ‘Warp drive’ anyone? At least one astrophysicist has mooted its theoretical possibility and compatibility with relativity theory: http://sydney.edu.au/news/physics_sifa/3134.html?newsstoryid=15346. You would have to slow down well before reaching your destination system if you were going to do any meaningful science – a leisurely 38kmps relative to us would be much more sensible (and safer for everyone, if Professor Lewis’s other prediction about coming out of warp drive is right!). So if it is artificial, Oumuamua’s current speed may not necessarily indicate how long it has taken to reach us from its home system. And the problem that Vega has moved a long way from Oumuamua’s apparent origin in the last 300,000 years is removed if the probe has actually taken only a few tens of years or less to get here. Although, if their observation skills really are that advanced, it might be a lot simpler and less expensive just to watch our TV.

  • ljk January 5, 2018, 16:45

    GeminiFocus, the magazine of the Gemini Observatory, has a cover article on ‘Oumuamua in is January, 2018 issue online here:

    https://view.joomag.com/geminifocus-january-2018/0667167001515088995

  • ljk January 9, 2018, 11:12

    1991 VG is just a rock, too…

    Suspected alien probe turns out to be lump of rock

    https://cosmosmagazine.com/space/suspected-alien-probe-turns-out-to-be-lump-of-rock

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