Oumuamua (1I) and Vega

Oumuamua is a small asteroidal object somewhere between 100 – 1000 meters long and is considerably longer than it is broad. Basically, it looks like a slab of rock, and is currently passing through the solar system on its way to wherever. It is our first observation of an interstellar object hence the bracketed formal name: 1 for first, I for interstellar. How do we know it came from interstellar space? Its orbit has been mapped, and its eccentricity determined. The eccentricity of a circular orbit is zero; an eccentricity greater than zero but less than one means the object is in an elliptical orbit, and the larger the eccentricity, the bigger the difference between closest and furthest approach to the sun. Oumuamua was found to have an eccentricity of 1.1995, which means, being greater than 1, it is on a hyperbolic orbit. It started somewhere where the sun’s gravity is irrelevant, and it will continue on and permanently leave the sun’s gravitational field. We shall never see it again, so the observation of it could qualify it for entry in “The Journal of Irreproducible Results”.

Its velocity in interstellar space (i.e.without the sun’s gravitational effects) was 26.3 km/s. We have no means of knowing where it came from, although if is trajectory is extrapolated backwards, it came from the direction of Vega. Of course it did not come from Vega, because when it passed through the space that Vega now occupies, Vega was somewhere else. Given there is no sign of ice on Oumuamua, which would form something like a cometary tail, it presumably came from the rocky zone closer to its system’s star, and this presumably has given rise to the web speculation that Oumuamua was some sort of alien space ship. Sorry, but no, it is not, and it does not need motors to enter interstellar space.

The way a body like Oumuamua could be thrown into interstellar space goes like this. There has to be a collision between two rocky bodies that are big enough to form fragments of the required size and the collision has to be violent enough to give the fragment a good velocity. That will also make a lot of dust. The fragments would be assumed to then go into elliptical orbits, but if there are both rocky planets and giants, the body could be ejected in the same way the Voyager space craft have left our solar system, namely through gravity assists. If the object is on the right trajectory it could get a gravity assist from an earth-like rocky planet, then another one from a giant that could give it enough impetus to leave the system. This presumably happened a long time ago, so we have no idea where the object came from.

Notwithstanding that, Oumuamua brought Vega to my attention, and it is, at least for me, an interesting star. That, of course, is because I have published a theory of planetary formation that is at odds with the generally accepted one. Vega has about twice the mass of the sun, and because it is bigger, it burns faster, and will have a life of about a billion years. It is roughly half-way through that, so it won’t have had time for planets to evolve intelligent life. The concentration of elements heavier than helium in Vega is about a third that of the sun. Vega also has an abnormally fast rate of rotation, so much so that it is about 88% of what would be required to start the star breaking up. This is significant because one of the oddities of our solar system is that the bulk of the angular momentum resides in the planets, while by far the bulk of the mass lies in the star. The implication might be that the lower level of heavier elements meant that Vega did not form cores fast enough and hence it does not have the giant planets of sufficient size to have taken up sufficient angular momentum. The situation could be like an ice skater who spins very fast, but slows the rotation by extending her arms. If the arms are very short, the spin cannot be slowed as much.

The infra-red emissions from Vega are consistent with a dust disk from about 70 – 100 A.U. out to 330 A.U. from the star (an A.U. is the distance from the sun to the Earth). This is assumed to have arisen from recent collisions of objects comparable to those in the Kuiper Belt here. There is apparently another dusty zone at 8 A.U., which would have to have originated from collisions between rocky objects. So far there is no evidence of planets around Vega, but equally there is no evidence there are none. We view Vega almost aligned with its axis of rotation, so most of the usual techniques for finding planets will not work. The transiting technique of the Kepler program requires us to be aligned with the ecliptic (which should be aligned with the equator) and the Doppler technique has similar limitations, although it has more tolerance for deviation. The Doppler technique detects the gravitational wobble of the star and if you could detect such a wobble directly, you could see it from along the polar axis. Unfortunately, we can’t, at least not yet, and worse, detecting such wobbles works best with very large planets around small stars. Here, if you follow my theory and accept the low metallicity, we expect small planets around a very large star. Direct observation has so far only worked for the first few million years of the star, where giant planets are radiating yellow to white light from their surface temperature that is so hot because of the gravitational accretion energy. These cool down reasonably quickly.

What grabbed my attention about Vega was the 8 A.U. dust zone. That can only be generated by a number of collisions because such dust zones have to be replenished. That is because solar radiation slows dust down, and it gradually falls into the star. So to have a good number of frequent collisions, you need a very large number of objects that could collide, which effectively requires a belt of boulders. So why have they not collided and formed a planet, when the standard theory of planetary formation says planets are formed by the collision of boulders to form planetesimals, and these collide to form embryos, which collide to form planets. In my ebook, “Planetary Formation and Biogenesis” I provide an answer, which is basically that to form rocky planets, the collisions have to happen in the accretion disk, and they happen very fast, and they happen because water vapour in the disk helps set cement. Once the accretion disk is removed, further accretion is impossible, other than from objects colliding with a big enough object for gravity to hold all the debris. Accordingly, collisions of boulder-sized objects or asteroids will make dust, and that would create a dust belt that would not last all that long. The equivalent of the Kuiper Belt around Vega appears to be between 3 – 6 times further out. In my theory, if the planet accreted in the same as the sun, it would be approximately 8 times further out. However, lower dust content may make it harder to radiate energy, hence accretion may be slower. If this second belt scales accordingly, it could correspond to our asteroid belt.  We know occasional collisions did occur in our asteroid belt because we see families of smaller fragments whose trajectories extrapolate back to a singe event. So maybe dust belts are tolerably common for short periods in the life of a star. It would not be a great coincidence we see one around Vega; there are a huge number of stars, we see a very large number of accretion disks, so dust belts should turn up sooner or later.

Finally, why does the star spin faster? Again, in my theory, the planets accrete from the solid and take their angular momentum, but then they also take angular momentum from the disk gas through a mechanism similar to the classical Magnus force. Vega has less dust to make planets, hence less angular momentum is taken that way, and because the planets should be smaller there is less gravity to take angular momentum from the gas, and more gas anyway. So the star retains a higher fraction of its angular momentum. All of this does not prove that my theory is right, but it is comforting that it at least has some sort of plausible support. If interested further, check out http://www.amazon.com/dp/B007T0QE6I.


5 thoughts on “Oumuamua (1I) and Vega

  1. Very interesting, Ian. Planetary formation is a subject in formation… and crucial, for giving us cosmic hope and purpose, an arrow for civilization…. Seems to me you are saying that HABITABILITY, usually interpreted as the water zone, also influences planetary formation crucially. I like it, a lot.
    (My own take on life creating planets is that they need to be in the radioactive belt… Habitability is a different notion…)

    • Not quite, Patrice. What I am saying is there are three temperature profiles at different times that are important. During stellar accretion, there is an important temperature around 1550 degrees C, where iron melts and certain aluminosilicates phase separate. This cools, and in the immediate aftermath of stellar accretion the rocky planets form. The critical temperature now is about current temperature, where the aluminosilicates can absorb water. (Venus failed here because ti was too hot, and never absorbed much water.) The third temperature is the habitability zone, which seems to be roughly the same as the second zone. Fort a successful planet to have life, all three have to be at about the same distance from the star. It seems as if number 2 & 3 are likely to coincide, but not with 1 except for G and heavy K stars. Red Dwarfs should have the first stage too close to the star, most of the time, but there are some further variables, such as the amount of dust and how fast the star accretes, so a general rule is difficult. The bad news is that once the system is formed, knowledge of the early stages is removed.

  2. Reblogged this on Patrice Ayme's Thoughts and commented:
    Last year saw the first out of Solar System object zoomed by. Some said it was obviously an extraterrestrial starship considering its shape and speed and origin:
    The subject is as philosophical as philosophical can be: Giordano Bruno was tortured for 7 years, and burned alive, after mutilations, just for claiming there were other star systems, with planets… (that offended the Jesus myth…).
    We need hope, a wider perspective: the cosmos provides them, even if we don’t get there, we can dream of it… Dreaming leads. Good dreams do best…. And displace nightmares… Loving the cosmos displaces hating neighbors…
    Planetary formation is a subject in formation… and crucial, for giving us humans cosmic hope and purpose, an arrow for civilization…. Seems to me you are saying that HABITABILITY, usually interpreted as the water zone, also influences planetary formation crucially. I like it, a lot.
    (My own take on life creating planets is that they need to be in the radioactive belt… Habitability is a different notion…)


  3. (CC comment on my site)
    There is a European mission going to Venus, it’s going to take years, using planet assist to… BRAKE!
    I think your idea that Venus got different because it was too hot for water to start with is spectacular…. But I have a problem with the fact the Sun (Sol) output is supposed to be 25% less 4 billion years ago… So it should have allowed water… Venus being at the limit of habitable zone…???

    • Oh, Venus had water. Just not as much. The water was, in my opinion, brought by binding with aluminosilicates. If cool, they can absorb a lot but as it warms, the amount they can absorb falls off quickly. The closer to the star, too, the more of the basaltic rocks formed large lumps. So the ratio of basalt to aluminosilicates increased the closer to the sun, and the ordinary silicates were much drier (like enstatite chondrites). Because the disk was dusty, probably sunlight was not that important – the heat came mainly from the gas still falling into the star, but the closer to the star, the more the stellar heat became significant. The prediction is that Venus does not have that much granitic material as Earth does (which is our continents).

      The significant question is where did the atmosphere come from? In my opinion, only solids accreted, and the carbon and nitrogen accreted as solids (carbides and nitrides, and other compounds) The closer to the star, the hotter, and more of these were accreted by Venus than Earth. The gases are formed by reaction of the carbides, etc with water. What happened was that Venus ended up with far less water, because of the heat, but more of these solids, and basically, most of the water was consumed by making the atmosphere. The reason for the exceptionally high D/H ratio is the chemical isotope effect, where the probability of a hydrogen atom being sent to space would be between 4 to 25 times greater than a deuterium. (The chemical isotope effect varies depending on what the reaction is.) The water oxygens provide the current CO2. The higher temperature is also why Venus has about four times the nitrogen than Earth has. Maybe I should do a bigger post about this.

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