Interstellar Visitor Stays Silent: No Signs of Life Yet on ‘Oumuamua

Dec 19, 2017

By Mike Wall

The first interstellar asteroid ever discovered in our solar system remains silent, at least for now.

An initial search for artificial signals coming from ‘Oumuamua, the needle-shaped interloper that zoomed past Earth two months ago, has come up empty, scientists with the $100 million Breakthrough Listen project announced today (Dec. 14).

But researchers aren’t done analyzing the data that came in from the Robert C. Byrd Green Bank Telescope in West Virginia yesterday (Dec. 13), and they also plan to conduct three more “blocks” of observations, team members said.

“It is great to see data pouring in from observations of this novel and interesting source,” Andrew Siemion, director of the Berkeley SETI (Search for Extraterrestrial Intelligence) Research Center in California, said in a statement. “Our team is excited to see what additional observations and analyses will reveal.”

‘Oumuamua has caused quite a buzz in the astronomy, planetary-science and SETI communities since the asteroid was detected in mid-October. The object’s trajectory reveals that it came here from another solar system, and its weird, extremely elongated shape has sparked speculation that the rock could be an alien spacecraft of some sort.

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27 comments on “Interstellar Visitor Stays Silent: No Signs of Life Yet on ‘Oumuamua

  • @OP – An initial search for artificial signals coming from ‘Oumuamua, the needle-shaped interloper that zoomed past Earth two months ago, has come up empty, scientists with the $100 million Breakthrough Listen project announced today (Dec. 14).

    That’s hardly surprising, considering it has the density of solid rock and is not even throwing off any dust, when warmed by our Sun.

    @OP – “It is great to see data pouring in from observations of this novel and interesting source,” Andrew Siemion, director of the Berkeley SETI (Search for Extraterrestrial Intelligence) Research Center in California, said in a statement. “Our team is excited to see what additional observations and analyses will reveal.”

    While it is worth checking out remote possibilities in rare opportunities like this, SETI enthusiasts do tend to indulge in fanciful wish-thinking!



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  • Alan4discussion #1
    Dec 19, 2017 at 10:22 am

    That’s hardly surprising, considering it has the density of solid rock and is not even throwing off any dust, when warmed by our Sun.

    There’s no way that I’m aware of of knowing its mass or density. I was actually thinking of writing a primer on mass measurement of celestial objects on the other thread but didn’t know if anyone would be interested.



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  • Arkrid Sandwich #2
    Dec 19, 2017 at 11:41 am

    There’s no way that I’m aware of of knowing its mass or density.
    I was actually thinking of writing a primer on mass measurement of celestial objects on the other thread but didn’t know if anyone would be interested.

    The report on th this link which was on an earlier thread, suggested it was dense.

    http://www.bbc.co.uk/news/science-environment-42053634

    “We also found that it had a reddish colour, similar to objects in the outer Solar System, and confirmed that it is completely inert, without the faintest hint of dust around it,” Dr Meech said.

    These properties suggest that ‘Oumuamua is dense, comprised of rock and possibly metals, has no water or ice, and that its surface was reddened due to the effects of irradiation from cosmic rays over long periods of time.

    Although ‘Oumuamua formed around another star, scientists think it could have been wandering through the Milky Way, unattached to any star system, for hundreds of millions of years before its chance encounter with our Solar System.

    The cosmic interloper was discovered by Rob Weryk, a postdoctoral researcher at the Institute for Astronomy and a co-author of the new study, which is published in Nature journal.

    I think calculations of density would be based on an estimation of volume based on the area of the images, the density based on the materials identified spectroscopically, and the gravitational deflections of it in passing large bodies of known mass. Structural integrity at higher rates of spin could also be relevant in small objects.



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  • Alan4discussion #3
    Dec 19, 2017 at 12:24 pm

    I think calculations of density would be based on an estimation of volume based on the area of the images, the density based on the materials identified spectroscopically, and the gravitational deflections of it in passing large bodies of known mass.

    The deflection of a small body by a much larger one is dependent only on the mass of the larger one. It tells you nothing about the mass of the small one. Any images and light curves of it are too imprecise to glean much more than a guess at its volume anyway. The word “dense” in the article you quote is just a speculation based on the colour and lack of a coma which would indicate ice or dust.



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  • The deflection of a small body by a much larger one is dependent only on the mass of the larger one. It tells you nothing about the mass of the small one.

    I’m not sure about that! When an object is falling on flyby trajectory, and being accelerated towards a more massive object, or slowed as it recedes from it, the inertia of the passing object must interact with gravity, with the strength of the attraction proportional to the (combined) mass. Velocities, changes in velocity, and changes in angle of deflection can be measured over time.

    We see deflections by small gravitational forces on small objects in the resonant frequencies of orbits in the moons of Jupiter and Saturn.
    We even see the Sun moving around its barycentre due to the gravity of distant planets!



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  • On the subject of deflections of objects of disproportional sizes, (albeit with one of them mechanically active), there is a study here:-

    https://www.space.com/13524-deflecting-killer-asteroids-earth-impact-methods.html

    The gravity tractor

    If researchers detect a potentially dangerous space rock in plenty of time, the best option may be to send a robotic probe out to rendezvous and ride along with it.

    The spacecraft’s modest gravity would exert a tug on the asteroid as the two cruise through space together. Over months or years, this “gravity tractor” method would pull the asteroid into a different, more benign orbit.

    “You can get a very precise change in the orbit for the final part of the deflection using a technology of this kind,” Schweickart said in late September, during a presentation at Caltech in Pasadena, Calif., called “Moving an Asteroid.”



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  • Arkrid Sandwich #4
    Dec 19, 2017 at 12:59 pm

    The word “dense” in the article you quote is just a speculation based on the colour and lack of a coma which would indicate ice or dust.

    I think you are correct in noting the lack of out-gassing of lighter elements as the prime indication of density.

    In cometary bodies, the deflection of orbital trajectories is primarily determined by directional out-gassing of volatiles and particles carried by those volatiles.

    In inert objects, the deflection of orbital trajectories is caused by locally stronger gravitational interactions, impacts, “Radiation pressure”, or the Yarkovsky effect – especially when acting on an irregular shaped body.

    With Oumuamua’s trajectory, passing close to the Sun inside the orbit of Mercury, there should have been out-gassing if volatiles were present near its surface.
    Solar radiation pushes neutral atoms away from Mercury, creating a comet-like tail behind it. The main component in the tail is sodium, so it is not just water or materials which are gaseous on Earth, which would vaporise at this point in Oumuamua’s trajectory if they were present.



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  • Alan4discussion #5
    Dec 19, 2017 at 2:01 pm

    The deflection of a small body by a much larger one is dependent only on the mass of the larger one. It tells you nothing about the mass of the small one.

    I’m not sure about that!

    That’s ok because I am.

    We even see the Sun moving around its barycentre due to the gravity of distant planets!

    Yes but you don’t see the sun moving because a tiny rock went by. Physics says it must but not by enough to measure. Only if an object is large enough to affect the movement of another known object by a measureable amount can its mass be detemined. In all other cases it’s the mass of the large object doing the moving that is revealed by the motion of the small object being moved.



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  • Arkrid Sandwich #9
    Dec 19, 2017 at 9:03 pm

    PS, what you’re in effect proposing is that heavy objects fall at a different rate than lighter ones which I’m pretty sure as a species we got past a few hundred years ago.

    No – when we are looking at an inert object approaching a star, (without out-gassing deflections), it is the Radiation pressure, and the Yarkovski effect whose influence on the exit trajectory are affected by density (mass/area ratio) and momentum. Very tiny differences multiply up over astronomical distances. (See gravity tractor example @#6) A lighter unpowered hollow space ship/probe, would not leave on the same track as a dense solid object.

    @#7 – In inert objects, the deflection of orbital trajectories is caused by locally stronger gravitational interactions,

    This was perhaps unclear. When I referred to “locally stronger gravitational interactions”, causing deflections of an asteroid in an eccentric orbit looping around a star, I was commenting on deflections from passing a planet on route, not a difference between lighter and heavier/denser objects.

    impacts, “Radiation pressure”, or the Yarkovsky effect

    It is these other causes of deflections which produce differences in trajectories of dense or less dense, less massive, objects.

    Sorry about the rather less than clear thinking and the unclear earlier explanations.



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  • Solar radiation pressure and the Yarkovsky effect are both miniscule and only affect objects over long time periods. For an object this size they’d be a couple of Newtons at most. Coming in at high speed over a short time frame they’d be far too small to measure in terms of its trajectory or be of any use in trying to calculate its mass. You can’t measure the mass of a non luminous celestial object unless it has something orbiting it. More detail posted now on the previous thread on this object.



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  • Arkrid Sandwich #11
    Dec 20, 2017 at 5:49 am

    Coming in at high speed over a short time frame they’d be far too small to measure in terms of its trajectory or be of any use in trying to calculate its mass.

    https://www.nasa.gov/planetarydefense/faq/interstellar

    Where is it going?

    Interstellar object 1I/2017 U1 is on an outbound trajectory. It will pass above Neptune’s orbit in 2022. As it leaves our solar system it is headed towards the constellation Pegasus.

    Yarkovsky effect @#7 link.

    The effect was first measured in 1991–2003 on the asteroid 6489 Golevka. The asteroid drifted 15 km from its predicted position over twelve years (the orbit was established with great precision by a series of radar observations in 1991, 1995 and 1999) from the Arecibo radio telescope.[3]

    Without direct measurement, it is very hard to predict the exact result of the Yarkovsky effect on a given asteroid’s orbit. This is because the magnitude of the effect depends on many variables that are hard to determine from the limited observational information that is available. These include the exact shape of the asteroid, its orientation, and its albedo.

    This does suggest a divergence of a few kilometres over a relatively short number of years – but probably not enough to measure density.

    Density would be much more clearly indicated by the melting point of any volatiles at perihelion indicating the possible chemical elements which are present or absent.



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  • There is some more information and a nice animation here:-

    https://solarsystem.nasa.gov/planets/oumuamua/indepth

    “For decades we’ve theorized that such interstellar objects are out there, and now – for the first time – we have direct evidence they exist,” said Thomas Zurbuchen, associate administrator for NASA’s Science Mission Directorate in Washington, in November 2017.

    Astronomers estimate that an interstellar asteroid similar to ‘Oumuamua passes through the inner solar system about once per year, but they are faint and hard to spot and have been missed until now. It is only recently that survey telescopes, such as Pan-STARRS1, are powerful enough to have a chance to discover them.



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  • Alan4discussion #12
    Dec 20, 2017 at 7:04 am

    Yarkovsky effect @#7 link.

    The effect was first measured in 1991–2003 on the asteroid 6489 Golevka. The asteroid drifted 15 km from its predicted position over twelve years (the orbit was established with great precision by a series of radar observations in 1991, 1995 and 1999) from the Arecibo radio telescope.[3]

    Without direct measurement, it is very hard to predict the exact result of the Yarkovsky effect on a given asteroid’s orbit. This is because the magnitude of the effect depends on many variables that are hard to determine from the limited observational information that is available. These include the exact shape of the asteroid, its orientation, and its albedo.

    This does suggest a divergence of a few kilometres over a relatively short number of years – but probably not enough to measure density.

    There’s a huge difference between 6489 Golevka and Oumuamua. Golevka is a solar system object already in a regular orbit so its expected path from gravity alone is known. Any deviation from that expected orbit can then be quantified in terms of other minor effects like solar radiation and those can be used to calculate mass.

    Oumuamua is not in orbit but making a single fly by so it doesn’t have a regular “expected” path and it’s not around for long enough and already too far away for other minor trajectory effects to be measured.



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  • Plus, when an object is in orbit then solar radiation is acting laterally on its path. When an object is leaving the solar system then solar radiation is primarily just pushing it from behind and not altering its trajectory.



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  • Arkrid Sandwich #14
    Dec 20, 2017 at 7:44 am

    Thanks for kicking around a few informative ideas as we look at this object.

    Oumuamua is not in orbit but making a single fly by so its mass (and density) cannot be calculated and it’s not around for long enough and already too far away for other minor trajectory effects to be measured.

    As I comment @#12, I think density is best indicated from the atomic weight of the elements identified by their presence of absence, and possibly the structural integrity of a rotating elongated object when under gravitational stress.

    I think this is the basis for the claims about density in the linked articles.

    Whether present technology can measure the density with sufficient accuracy or not, the density interacting with the effects mentioned, will affect its exit trajectory and next destination millions of years hence!



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  • Arkrid Sandwich #15
    Dec 20, 2017 at 8:01 am

    Plus, when an object is in orbit then solar radiation is acting laterally on its path. When an object is leaving the solar system then solar radiation is primarily just pushing it from behind and not altering its trajectory.

    That becomes progressively true as Oumuamua’s distance from the Sun increases, but for a significant part of the eccentric loop trajectory, it is flying at an angle to the solar radiation. (#13 animation)



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  • In terms of solar radiation being able to affect anything on a body that large it’s still an insignificant time while Oumuamua is looping round the sun. A few days. After that it’s basically flying straight away from the sun. And anyhoo, this has nothing to do with your contention that you can determine the mass of a body from how it reacts to other body’s gravitational fields which is plain wrong.



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  • Arkrid Sandwich #18
    Dec 21, 2017 at 12:31 am

    And anyhoo, this has nothing to do with your contention that you can determine the mass of a body from how it reacts to other body’s gravitational fields which is plain wrong.

    That would be wrong, and I am sorry for the earlier unclear comments while I was pondering the mechanisms, but the issue is not simply about the mass and gravity, but about the interactions of all the factors affecting the orbital trajectory, and the basis for estimating its composition and density.

    @#19 – Is anyone following this thread or has it got too technical?

    I think we might be getting a bit too technical, but there may be some specialist interest. It is probably a topic which is going to be both technical and speculative by its very nature.



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  • I calculated the g forces involved from the tumbling that this body is experiencing using the size and rotation estimates available online. Pretty negligible. An ant living on one end of Oumuamua would only be experiencing about 1 millionth of a g. It could be made from swiss cheese and not fly apart. Nothing much in that to tell us what it might be made from.



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  • I also ran all the maths involved in gravity tractors and programmed a spreadsheet to design them. There’s a Wiki article on them but the assumptions in it are dubious and the maths don’t stand up to scrutiny. Maybe best I don’t go into that here though.



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  • Arkrid Sandwich #21
    Dec 21, 2017 at 9:25 am

    I calculated the g forces involved from the tumbling that this body is experiencing using the size and rotation estimates available online. Pretty negligible. An ant living on one end of Oumuamua would only be experiencing about 1 millionth of a g. It could be made from swiss cheese and not fly apart. Nothing much in that to tell us what it might be made from.

    I think they would be, unless it approached or flew-by a star or a large planet, as examples of comets approaching Jupiter show.

    The ranges of gravitational attraction which hold together asteroids, comets, moons, and planets, are fascinating.

    Mercury’s gravity is too weak to retain a moon, and the solar wind is tearing off its heat-generated metallic atmosphere, but by the time we look out in the Solar-System as far as Pluto, this dwarf planet, has moons which appear to have self-assembled from collision debris – including materials which are volatiles in the inner Solar-System.

    https://www.nasa.gov/feature/new-data-compare-contrast-pluto-s-icy-moons

    Further out in the Kuiper belt even smaller bodies can maintain orbiting fellow travellers.
    Who knows what configurations may be found in the Oort cloud, where our Sun’s gravity is tiny?



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  • phil rimmer #24
    Dec 22, 2017 at 8:39 am

    Thanks, chaps. Not too technical at all, surely? All good High School/A level stuff.

    Pretty basic to anyone who got a good education but not many fall into that camp. It always amazes me that people can spend the same number of years at school as I did but come out at the end of it knowing more or less nothing. I was lucky enough to go to a fee paying public school and got a first class education in science, maths, the classics, languages etc. My best mate went to a Scottish comprehensive and learned little more than basic reading and writing. He has no idea what Pi is for example.



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  • Alan

    We find this disparity in the US as well but it’s also seen between those who had a public (taxpayer funded) education in a wealthy town or a poor town. Public education in a wealthy town can provide an education on par with an expensive private school but woe to those poor kids who have the bad luck in life to have been born into failing school systems in the urban concrete jungles and the impoverished rural areas. Those towns and cities have a meager tax base and therefore struggle to provide even the lowest level of education to their students.

    This is the foundation of a society segregated by race and economic class.



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  • Arkrid Sandwich #21
    Dec 21, 2017 at 9:25 am

    I calculated the g forces involved from the tumbling that this body is experiencing using the size and rotation estimates available online. Pretty negligible.

    However, for this elongated structure to remain after withstanding the forces from a collision, it needs to be much more robust!

    http://www.bbc.co.uk/news/science-environment-43018706

    The space interloper ‘Oumuamua is spinning chaotically and will carry on doing so for more than a billion years.

    That is the conclusion of new Belfast research that has examined in detail the light bouncing off the cigar-shaped asteroid from outside our Solar System.

    “At some point or another it’s been in a collision,” says Dr Wes Fraser from Queen’s University.

    His team’s latest study is featured in Sunday’s Sky At Night episode on the BBC and published in Nature Astronomy.

    Dr Fraser and colleagues could see that it was not spinning periodically like many small asteroids, but spinning chaotically – it was tumbling.

    The most probable explanation is that ‘Oumuamua has been hit by another object at some point in its history.

    “The tumbling actually causes stresses and strains internal to the object, and that slowly but surely squeezes and pulls on the object just like tides on the Earth to remove energy from the spin,” explains Dr Fraser. This dampening process takes a very, very long time.

    Dr Fraser says it is reasonable to assume the collision occurred in ‘Oumuamua’s own stellar system before it was then kicked out.

    “It’s hard to know if it was during planet formation or after the planet formation process,” he tells Chris. “Certainly, more collisions happen while planets are growing than afterwards, so that’s a very good guess. But unfortunately we can’t get a high-resolution image of this thing to see what kind of crater is on it that might be attributed to the collision that caused it to start tumbling.”

    The hunt is now on for more ‘Oumuamua-like objects. Extrapolating from this one discovery, there ought to be some 10,000 of them passing through our Solar System inside the orbit of Neptune.

    The trouble is – being so small and dark, they are extremely hard to spot.

    There is though, a new observatory coming that may change this game completely. It is called the Large Synoptic Survey Telescope and it will come online in the next couple of years.

    With its 8.4m primary mirror and super-digital camera, it will image the entire viewable sky from its position in Chile every few nights.

    If anything is moving across the sky, it will be hard to escape the attention of the LSST.

    “It is basically the perfect sort of tool to find objects like ‘Oumuamua. We expect to find 100s of them with the LSST,” Dr Fraser says.



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