New evidence for the nature of interstellar object ‘Oumuamua is in, making it far more likely that the unusual interloper is a comet rather than an asteroid. The data come from an array of instrumentation — the Hubble Space Telescope, the Canada-France-Hawaii Telescope, ESO’s Very Large Telescope and the Gemini South Telescope — and show that `Oumuamua is slowing down slightly less than expected. We are talking about a tiny force, about 1/1000 as strong as the pull of the Sun’s gravity, according to this overview of new work in Nature.
The science paper on this work, which also appears in Nature, looks at a variety of possible explanations for the velocity change. The one the authors think most likely is that `Oumuamua (pronounced “oh-MOO-ah-MOO-ah”), now moving at some 114,000 kilometers per hour, has vented material during its pass through our system, behaving the way many comets do. Marco Micheli (ESA), lead author of the paper, puts it this way: “We can see in the data that its boost is getting smaller the farther away it travels from the Sun, which is typical for comets.”
Co-author Karen Meech (University of Hawaii) concurs. It was Meech who led the initial discovery team characterisation in 2017. Although the scientists found no visual evidence for outgassing, it remained true that the composition of its surface resembled a cometary nucleus. Meech adds: “We think that ‘Oumuamua may vent unusually large, coarse dust grains.” If passage through interstellar space had eroded smaller dust grains on the surface of the object, a cloud of larger particles would not have been bright enough for Hubble to detect.
Image: This artist’s impression shows the first interstellar object discovered in the Solar System, ʻOumuamua. Observations made with the NASA/ESA Hubble Space Telescope, CFHT, and others, show that the object is moving faster than predicted while leaving the Solar System. Researchers assume that venting material from its surface due to solar heating is responsible for this behavior. This outgassing can be seen in this artist’s impression as a subtle cloud being ejected from the side of the object facing the Sun. Because outgassing is a behavior typical for comets, the team thinks that ʻOumuamua’s previous classification as an interstellar asteroid should be changed to a comet. Credit: ESA/Hubble, NASA, ESO, M. Kornmesser.
For my part, I like the description offered by Michele Bannister (Queen’s University Belfast) in the article cited above. Bannister compares the object to a “‘baked Alaska’ dessert, with a frozen heart and warm exterior.” An object like this, approaching the Sun, would begin outgassing, though the rate here is tiny. Let me quote from the Nature article:
The outgassing rate is small compared to what typical comets experience, says Jessica Agarwal, an astronomer at the Max Planck Institute for Solar System Research in Göttingen, Germany. ‘Oumuamua also emits relatively little debris, perhaps because its dust particles are too large and heavy for the weak outgassing to carry aloft. That could explain why ‘Oumuamua never developed a visually stunning, comet-like tail.
Comets can be affected by non-gravitational accelerations, however, as ‘Oumuamua now apparently shows. From the paper:
After ruling out solar-radiation pressure, drag- and friction-like forces, interaction with solar wind for a highly magnetized object, and geometric effects originating from ‘Oumuamua potentially being composed of several spatially separated bodies or having a pronounced offset between its photocentre and centre of mass, we find comet-like outgassing to be a physically viable explanation, provided that ‘Oumuamua has thermal properties similar to comets.
The paper also considers solar radiation pressure, the Yarkovsky effect (in which thermal variations on the surface of a rotating object like an asteroid can lead to asymmetric forces), and the possibility of a collision with another object, none of which fit the bill. The unlikely idea that `Oumuamua is an alien spacecraft is rejected because the object is tumbling on all three axes. Our short-term interstellar guest, in any case, has been nudged a bit faster than expected.
Assuming we’re dealing with a comet, the outgassing may make our attempts to trace its home star that much more difficult. The new observations were carried out to help make that call, but team member Olivier Hainaut (European Southern Observatory, Germany) now wonders whether we will ever know its true home. As to its apparently cometary nature, he adds:
“It was extremely surprising that ʻOumuamua first appeared as an asteroid, given that we expect interstellar comets should be far more abundant, so we have at least solved that particular puzzle. It is still a tiny and weird object that is not behaving like a typical comet, but our results certainly lean towards it being a comet and not an asteroid after all.”
The paper is “Non-gravitational acceleration in the trajectory of 1I/2017 U1 (`Oumuamua)”, Nature 27 June 2018 (abstract).
Comments on this entry are closed.
There are two problems with this scenario that the writers of the Nature article are suggesting: (a) no outgassing has been detected – indeed, as I understood but I may be wrong, outgassing had previously been positively eliminated because none was seen; (b) since Oumuamua appears to be rotating chaotically, any outgassing jet from a fixed point on the surface would be wobbling all over the sky, and hence would not be expected to contribute much net acceleration.
There is also the subsidiary point that, if outgassing is indeed taking place, this would imply that Oumuamua is made largely from ices, probably mixed with pebbles and other debris, and hence that its material is relatively soft and flexible. But an object that is tumbling chaotically gradually loses rotational energy (but not angular momentum) due to repeated deformation in different directions, and previously the chaotic nature of Oumuamua’s rotation has been said to prove that its material is very solid and unyielding.
Leaving aside all the woffling, what this new development amounts to is that the authors claim to have discovered that Oumuamua was not pursuing a purely inertial trajectory, but was being accelerated gently away from the Sun by some unknown influence.
This dramatically points up the relevance of speculations about an Oberth maneuver – already given much credibility by the peculiar nature of the trajectory.
I am deeply skeptical that we currently have any real idea about what this mysterious body actually is/was.
An Oberth effect: most intriguing indeed. Did it stop its 3-axis tumbling near the sun, or is there a way to control the direction of the exhaust while the tumbling continues?
If it is a comet the strongest of the out-gassing should occur on the side that is heated directly by the Sun. Even if it’s chaotically tumbling, for every piece of ‘Oumuamua’s surface you would get more ice to sublimate instantly while it’s washed by the Sun’s light, then as soon as this area is back in the dark, the surface would start slowly to cool down and the out-gassing would be less and less intense, until it’s facing the Sun again. therefore it should logically accelerate away from the sun on its outbound journey even if it’s tumbling. But while falling towards the Sun this same out-gassing effect should have slowed it down a bit, decreasing the altitude of its perihelion compared to the case of an inert asteroid falling towards the Sun from the same origin.
This is the first time I have ever heard of the “Oberth maneuver”. The article states that `Oumuamua is SLOWING DOWN the farther away it gets. Is THIS CONSISTENT with an Oberth maneuver?
No. The thrust gets weaker the further away from the Sun it gets.
The Oberth maneuver is about maximizing velocity with the propellant energy by using the thrust when at closest approach to a body. This may be consistent with the maximal ejection of gases when close to the sun. If Oumuamua is slowing down faster than expected, I don’t think it has anything to to do with the OE.
Do comets generally eject material on the side facing the sun and therefore accelerate more slowly than freefall approaching the sun and vice verse when receding back towards aphelion? Or do different effects appear during their obit?
My misinterpretation somewhere. Oumuamua is decelerating more slowly than expected, ie there is some thrust from the object. That seems consistent with net mass ejection from the sunward facing side as the object exits the solar system.
It is indeed slowing down, as should any inert object in a gravity field on a outward trajectory. Indeed, the Sun’s gravity continues to pull the object towards the Sun while it is going away, like when you throw an object vertically towards the sky, it slows down and then falls back. The article says it’s slowing down LESS than expected. Meaning there’s some kind of force fighting against the Sun’s gravity. But very weakly, only a thousandth of the gravity exerted by the Sun. So it’s still slowing down, just 1/1000 less than expected.
Yes it is. Even with an Oberth manoeuver you WILL slow down the farther you get. Unless you burn indefinitely, but that’s not exactly how you oberth. The OE is usally used as a mean to save fuel by converting potential energy into kinetic energy, so you burn only at the periapsis, then you just coast. While you coast, you do slow down because gravity is still pulling you backwards, but hopefully less that the tremendous acceleration you got from the OE.
I wish we had a slow moving production line churning out New Horizons class spacecraft every now and then. We could use many :) What an opportunity this would be!
Let’s not forget to put the flyby effect into the mix of possibilities. ‘Oumuamua did buzz the Sun fairly closely at perihelion.
Egad, that’s an interesting mystery there! I wonder–although it isn’t listed as one of the proposed explanations for the flyby anomaly–if the Earth’s magnetic attraction on those probes might account for the tiny velocity discrepancies? Just as regular space probes aren’t solar sails (yet the effect of sunlight pressure on them must be accounted for when plotting their courses, as it causes large trajectory dispersions of thousands of kilometers over months or years), ordinary probes aren’t magsails, either–but the Earth’s “bar magnet” dipole magnetic field pulls slightly on the ferromagnetic metals in their structures.
Maybe the Pioneer anomaly is at work here (one could argue that it only applies to Ames Research Center probes, since it doesn’t affect the [JPL] Voyagers and the [JHU/APL] New Horizons spacecraft)… :-) Also:
I don’t recall the issue or the exact distance involved, but I recall reading–in an issue of either “Astronomy” or “Sky & Telescope,” when I worked at the now-closed Miami Space Transit Planetarium between 1989 and 1993–that an unexpected outburst from the receding nucleus of Halley’s Comet, then billions of miles from the Sun, was observed by (I think) one of the Keck telescopes. The outburst, occurring that far from the Sun, could have been due to an impact, and:
Since ‘Oumuamua is far smaller–and lighter–than Halley’s nucleus, an impact (on its anti-sunward side), or another sort of outburst that produced thrust on that side (maybe an impact by a very small object or swarm of particles, that exposed a low sublimation-temperature frozen volatile [or mixture of volatiles] below ‘Oumuamua’s surface?) could produce a significant braking effect, slightly slowing its “climb” away from the Sun.
Remember when Comet Holmes had its unexpected outburst in 2007? That object orbits between Mars and Jupiter so presumably solar heating was not to blame. Holmes had done this before in 1892 which is how it was first discovered.
” . . . team member Olivier Hainaut (European Southern Observatory, Germany) now wonders whether we will ever know its true home. ”
Papa was a rolling stone.
Wherever he laid his hat was his home.
Life of the interstellar scout . . .
Need I mention the possibility that ‘Oumuamua buzzed our system, a possible stealth scan to get some idea of our capabilities? More than a few commentators have wondered. This seems almost a slam-dunk, though of course “extraordinary claims require extraordinary evidence”.
If scan then gentle seemingly random tumbling would have a couple of effects. First, it appears natural. Second, even out all internal heating and cooling effects with less effort (i.e. the Apollo craft had to rotate to not bake things.)
Meanwhile: does anyone have an *exact* length of this thing, and does that translate to anything? Am thinking of the type of thing where a dipole antenna length depends on frequency range. Although this wouldn’t be a dipole does the length tell us anything?
Astronomers are still debating whether Oumuamua is shaped like a shard or a pancake. A deep space probe would resolve that question and others.
I don’t know if ‘Oumuamua’s exact dimensions are known, but I follow your reasoning (assuming that it’s artificial, which I doubt, but don’t know one way or another). If it is a reconnaissance probe (particularly a “ferret,” a signal-monitoring probe) disguised as a natural object (the asteroid 1620 Geographos also appears to have a quite high fineness ratio [length/diameter ratio], so high fineness ratios aren’t unknown among natural celestial objects), I can picture ‘Oumuamua as follows:
The probe’s long body could be a radome, made of RF-transparent material (fiberglass is just one such material, of course), perhaps disguised to look like an asteroid from the outside. Inside could be multiple dipole antennas, cut (and/or inductor-loaded) to resonate across wide bands of radio frequencies, with electronic antenna switches to enable the receivers to listen across many channels nearly simultaneously, and:
It would even be possible to instead hide one large dipole, a “sleeve” of wire screen or metal foil that’s electrically cut in the middle, just under the surface of the probe’s cylindrical body (the Explorer 1 – 4 satellites’ bodies were such dipole antennas). This “body dipole” could be tuned using inductors and capacitors to resonate across a very wide frequency range. Also, spin-scan infrared and visible-light sensors (including radiometers, polarimeters, and imagers) could be placed at the probe’s ends, hidden in false craters and fissures in the object’s surface.
I doubt that this is artificial as well, but the shape is unusual and as another poster observes, it did manage to fly right through a habitable zone. Hence we are obligated to speculate on the potential for artificiality.
We make gravity detection devices these days where the detection relies on things placed at a known opposed distance. I am supposing that a comms device [quantum?] could possibly require similar properties. This would in turn dictate the size/shape. We would not be able to detect anything with our present state of technology; it would appear to be inert. [Spooky action at a distance implies possible FTL communication.]
If I were engineering a probe and not wishing to alarm or alert the target, it would probably look and behave exactly as this thing does.
Regarding the acceleration, wouldn’t *any* object in space be subject to outgassing when slammed with cosmic radiation and photons and solar wind and such? I am not sure why outbound acceleration would follow an ‘ideal’ path, and I’m surprised that anyone is surprised. Even Musk’s space Tesla should be subject to radiation messing with the materials and making them behave differently when slammed with photons [starting with the tires and interior plastics I think.]
The 3-axis tumbling also could be a totally unintended outcome with an artificial interstellar probe. It’s not inconceivable over the wide reaches of space and time that a probe might lose attitude control from some internal and/or external cause. When we talk about sending out all these possible interstellar probes to do — flybys much like ‘Oumuamua — one wonders how many will reach their destination without some sort of snafu along the way.
“That which doesn’t kill you sometimes just leaves you spinning uncontrollably toward your ultimate destination.”
“That which doesn’t kill you sometimes just leaves you spinning uncontrollably toward your ultimate destination.”
“That which doesn’t kill you sometimes just leaves you spinning uncontrollably toward your ultimate doom.”
“Extraordinary claims require extraordinary evidence”: not only did ‘Oumuamua “buzz our system,” it made a beeline for the habitable zone. This counts, of course, only as circumstantial evidence for an alien probe; still, this trajectory, if random/natural, is then extraordinarily coincidental.
Astronomers had not been able to successfully detect an interstellar object coming through our Sol system until just recently. They claim that between one and ten such celestial bodies wander through our celestial neighborhood every year. When we start detecting more of them and can build up a database, then we can figure out what they are really all about.
As for hints and claims that Oumuamua is an artificial ETI probe, we need a LOT more evidence. That is why we should have had a deep space probe ready to go. Maybe the powers that be will wake up now and be ready next time. Or even still consider sending one to Oumuamua since it is the only example of its kind we have right now.
In Episode 12 of “Cosmos” (‘Encyclopedia Galactica,’ see: http://www.youtube.com/watch?v=m-NIwzBFJ_Y ), at the 54:40 point Carl Sagan mused that one day, such an encyclopedia may contain an entry for the Earth–or that even now, perhaps as a result of a “discreet survey mission,” our world and humanity might already be so listed, and:
I am not saying that ‘Oumuamua’s odd passage through our solar system (including its close approach to the inner solar system) was such a “discreet survey mission,” but if we were to conduct such a mission ourselves, we might do something similar. Whether ‘Oumuamua is artificial or natural (I think it’s the latter, but one never knows without a close look), I think it is well worth visiting, being the first and only–so far–indisputably interstellar object that we have seen.
The problem with the comet theory is the ratio of length to width, ~10 to 1 which is very unlike comets.
Well people also used to say that a hourglass was a very unlikely shape for a comet’s core, then came Chury.
With such a low surface gravity and potentially violent formation histories, I would never again presume of any asteroid or comet’s shape.
How do you feel about a pancake:
DEFINITELY!!! It’s the Millennium Falcon with all that space-grease they just discovered caked onto it. lol.
Millennium Pattie more like it and that impact crater would likely have gone straight through. I still think it is an asteroid perhaps with a coating of lose regolith, perhaps electrostatics is playing a part.
Nature is really REALLY on a roll this week! CHECK THIS OUT!!! Nature 558: 564-568 (2018). https://doi.org/10.10318/s41586-0246-4. “Macromolecular organic compounds from the depths of Enceladus.” by Frank Postberg et al. PREMISE: …”Until now, omly simple organic molecules of less than 50 atomic units have been detected in the plumes, NOW: …”Ice grains containing concentrated and complex macroscopic organic material with molecular masses above 200 atomic units have now been found…” that FLOATS between the ocean water and the ice crust! OIL SLICK ANYONE!!!!!!!!!!
Someone needs to check up on Yuri Milner – and maybe get an interstellar visitor probe in the mix:
Also check in with Musk and Besos.
Not to mention the recent claim that interstellar space has carbon in the form of grease as a major component. No wonder so many bodies are covered in organic goop.
WOW! The authors believe that these 200+ atomic mass particles are actually just FRAGMENTS of what used to be MUCH LARGER(i.e THOUSANDS of atomic mass)molecules! POLYMERS ANYONE!!!!!
Now we just need to sample Europa’s geysers to see if it contains similar ingredients.
Well, there is a fuzzy line between very dirty comets and “damp” asteroids.
Indeed. Most asteroids aren’t very dense, much more like big balls of dust than solid chunks of rock. Just add pebbles of water ice, carbon monoxide ice and methane ice to the mix and you get a comet.
We should still attempt to send a space probe to Oumuamua. It is real and we know where it is, and it is still not out of reach.
Failing that, we should have one or several such robot explorers built and ready to go for the next such interloper and any other celestial surprise in our planetary neighborhood. We do not lack the technical ability for this.
Astronomers have said we should expect between one and ten interstellar visitors to our Sol system EACH YEAR. So let us get ready for the next one.
‘Astronomers have said we should expect between one and ten interstellar visitors to our Sol system EACH YEAR.’
Hmmm why do I have a hunch this is not going to be the case… 8 months and counting.
Such a probe and its “launcher” (the probe proper, mated to a separable stack of STAR-type spherical solid propellant rocket motors) could also “earn its keep” while waiting for interstellar interlopers to chase after. A small instrument/imager package (which would make it unnecessary for the main Lyra-type probe to extend its booms until after it was injected into its intercept trajectory) could observe the Moon’s far side–and also the tiny, temporary asteroidal moons that the Earth regularly captures (statistically, we always have one or two, orbiting about a million miles out)–while waiting in a “holding orbit” for an interstellar object to pursue.
From the other side:
Could the unusual light curve be an encoded message? Has anybody tried looking at its characteristic to see if any recoverable data may be encode in the light curves. Just as we advertise with light patterns maybe it was looking for an optical signal to stop and sell its goods! Might be worth the effort and if nothing else a good way for SETI to analyse something on a possible different level of exterestrial contact.
“Could the unusual light curve be an encoded message? Has anybody tried looking at its characteristic to see if any recoverable data may be encode(d)”?
It would indeed be prudent to leave no stone unturned in this unusual episode. The gargantuan decrypting power and resources of the NSA could be useful in this regard.
Maybe we can be ready for the next two that do a fly by of the sun. Remember they are suppose to come in threes. (Only kidding!!!)
This may or may not be useful in regards to Oumuamua’s behavior…
NEW MYSTERY DISCOVERED REGARDING ACTIVE ASTEROID PHAETHON
Based on a new study of how near-Earth asteroid Phaethon reflects light at different angles, astronomers think that its surface may reflect less light than previously thought. This is an exciting mystery for the recently approved DESTINY+ mission to investigate when it flies past Phaethon.
Full article here:
What would it be like to stand on the surface of Ryugu?
But, as I pointed out in my previous post, Ryugu is a fast rotator, spinning once every 7.5 hours or so. That’s important! If you’re on a spinning object there’s an acceleration (called centripetal acceleration) that you feel as a force pushing you away from the center of the spin. It’s the same thing as when you’re in a car making a turn and you feel a force in the direction opposite the turn (if you turn left you’re thrown right, which is the same as saying you want to go straight but the car turning left makes it feel as if you’re being pushed to the right).
This counteracts the force of gravity down, toward the center of Ryugu. I played with the math a bit, and found that on the equator the force outward is about 1/5th or so of gravity! So you’d weigh noticeably less on the equator than you would at the poles just because of this.
If you’re not on the equator, that force outward points at an angle away from the center of Ryugu. The net effect is it would feel like you’re standing on a slope, downhill toward the equator, even if the ground were perfectly flat! So if you’re a rock sitting on Ryugu halfway between the equator and pole, say, and there’s a small impact by another asteroid, the ground would shake, dislodging you, and you’d roll toward the equator.
I strongly suspect that’s why Ryugu has the shape it does. Stuff has rolled “downhill” toward the equator, piling up there, forming that ridge all the way around, giving it a more diamond-like shape than spherical. If it’s a rubble pile, there’s a lot of loose material available to do this, too. So these ideas hang together.
A considerable amount to digest here and a fair amount of reading; as well as a relatively detailed analysis.
But the moment I began to scan the total article as well as the comments, one thing began to form as an idea within my mind.
If anybody remembers the story behind Apollo 13, one thing that stands out in my mind is the fact that during the tracking phase of the spacecraft to make a velocity and position determination, they insisted that the astronauts perform no more urine dumps overboard.
They distinctly forbidden the practice so that they could obtain a far more precise fix on the Doppler shift by which they could do their tracking.
Now, this is (and should not be considered a) complete and thorough analysis of the situation, but if we actually have a cometary body, which is undergoing some type of subtle and intermittent outgassing phenomena, could that possibly be the reason why we are seeing a (supposedly) subtle velocity shipped from the expected value.
After all, I presume that they are performing tracking of this object by radar and they are seeing Doppler shifts that would seem to confirm and anomalous and unexplained velocity. Additionally, might there be radiation pressure as well as gravitational mass uncertainties that could completely account for these velocity anomalies ? These would seem to be more likely than some mysterious explanations (i.e., an artificial satellite). What does other people think of these type of explanations ?
Well it’s definitely not an alien spacecraft, it’s just blowing swamp gas! ;-)
Maybe they spaced their tyrannical captain for an extra boost to escape detection.
Just wondering if the asteroid has become highly electrostatically charged due to its long interstellar journey. This electrostatic charge interaction with the outgoing solar wind would cause a very small acceleration.
One thing that doesn’t seem to be discussed by anyone who is playfully offerring the ‘artificial scout’ line is the enormous trajectory change. Yes, by definition ETI thinking is alien to us, but it seems a very inefficient way of exploring many systems… this thing came in and almost did a 180 before heading off out again. Just thought I’d bring it up.
5 things we know – and 5 we don’t – about ‘Oumuamua
By EarthSky Voices in Space | July 15, 2018
Mysterious ‘Oumuamua is the 1st confirmed interstellar object to pass through our solar system.
“…the classification of ‘Oumuamua as a comet is questionable”