A Planet Here Today and Gone Tomorrow

Or, a record for the biggest thing lost! Or, to loose your car keys is careless, but to lose a planet??

As some readers will know, I have my own theory of how planets form from the dust of the accretion disk around stars. The dust is actually micron sized, and finer than an average smoke distribution, and as the gas falls into the star, it gets hot, its potential energy lost being converted to heat, and when it gets hot enough it glows. Of course, it also glows by scattering light emitted by the forming star hence we observe those disks. Standard theory assumes planets form through gravity. The problem here is gravity is far too weak to aggregate this dust, so the standard theory assumes that somehow it forms planetesimals and there is an even distribution of these out to about 32 A.U. (one A.U. is the Earth-Sun distance) where their density falls off dramatically for some unknown reason, although it is necessary they do to prevent more planets being formed further than Neptune. While this is needed to make the theory fit the facts, it is not exactly enlightening, and it is far from clear why Neptune has far more mass than Uranus.

Anyway, I find all this unsatisfactory on many counts. My concept is that getting started involved chemistry, or physical chemistry, in which case what you get depends on the local temperature during accretion. In principle this is quite predictive; in practice not so much because we do not know what the temperatures were for a given system because all evidence of the disk for all systems older than 40 My is long gone. The temperatures depend on the potential energy converted, but that depends on how fast the star is accreting, i.e. the rate of conversion, and for a given size of star, this can vary by a factor of ten. However, there are proportional predictions, i.e. if you have a distribution of planets, it predicts how they should be spaced and what their relative properties should be. Thus besides explaining why Neptune is more massive than Uranus, and there are no planets further out (actually, it does predict the possibility of more, but very far out). It also predicts no life under ice at Europa because the theory predicts there are no significant amounts of nitrogen or carbon, which is verified by observation.

When I published my ebook on planetary formation in 2012, by and large the known observed data matched predicted data surprisingly well, although there was not that much respectable data on multiple systems and for single exoplanets, variation up to an order of magnitude was “tolerable”. However, much of what was generally predicted appeared right, thus red dwarfs, because they had much less material, were expected to have planets closer to the star, and they were. But there was one annoying feature. The star Fomalhaut has a rather odd accretion disk around it, and it appears with the brightest part as a ring very distant from the star. My guess is the star is in the process of ejecting the disk, but maybe that is wrong. Anyway, the disk had a planet that could be seen in a telescope. The problem was, it was somewhere between 100 – 250 A.U. from the star. That by itself was no problem; the star is huge, so planets will be well spread. The problem was, if it were that bright, you should be able to see others, and there were no others. As it happens, this week the problem has gone away because the planet has gone away. More specifically, it was never there. Maybe that should have been suspected. Its light distribution was quite odd, being surprisingly bright in the visible, but seemingly less so in the infrared, which was indicative of surprising heat. Newly formed gas giants can be very hot, due to the energy of the gas falling onto them, so nobody took much notice. However, after a very short time it faded, and now it cannot be seen. What we now think happened was that a collision took place between two objects about 250 km long, and we saw the extreme heat so generated. A very rare occurrence indeed.

2 thoughts on “A Planet Here Today and Gone Tomorrow

  1. Interesting consideration for the lack of life inside Europa… Well then so much the better, we can engineer our own…
    At least one asteroid to asteroid collision was observed in the solar system: we have a movie of it!

    There is a recent article in the New York Times showing the movie of the apparition and disappearance of the Fomalhaut b “planet’, from Hubble pictures. It really looks like an explosion… And the cloud took a decade to dissipate, just as theory predicts.
    I don’t see why standard gravitation theory doesn’t predict planet accretion. First the mass of a dust cloud could be many solar masses. It collapses under its own gravity. At it does, the slightest rotation is converted, through angular momentum conservation into a massive rotation of a disk… This star system formation theory comes from Laplace. The same rough picture applies to form galaxies… and planets! If a cloud shaped as a doughnut is the mass of Jupiter, even if in orbit, around a star, it will end up collapsing on itself, from some irregularity… and the rotation on itself, in the correct sense will be generated from the orbital motion (as observed!… mostly).

    The cloud around the star doesn’t have to be even, nor does the disk then, hence haphazard planetary mass distributions (as observed). However one would expect more mass towards the center… Thus Jupiter-like planets to be towards the center (as observed: the “hot Jupiters”)… As the central mass becomes a star, radiation pressure enters the mix. So one would then expect many of the hot Jupiters to be torn apart, losing their gas 9except for hot Jupiters which are massive enough!), leaving rocky planets behind (as observed), or then that rocky planets would form towards the interior from sinking of the densest elements (as observed).

    Right, these are contrary, alternative scenarios. However, stars are not all the same, thus neither are radiation pressures: a tiny red dwarf (75% of stars) is nothing in common with a blue supergiant (a future supernova).

    In any case, exciting days. Instead of propping up the useless and degenerate non-essential economy, the frivolity of which the Corochinavirus is thoroughly demonstrating, to my great satisfaction. Instead, humanity should do something really useful, and build a 200 meters across telescope… there are lots of questions about the Centauri system, including that of the exoplanet closest to Earth, apparently a sort of super-earth… Is it alive? Inhabitable? First we should find out how big it really is…

    • I was unaware there had been an asteroid collision, so thanks, Patrice. As for the rest of what you write, there is enough material there for several posts, but my primary feeling is there is too much space for planets to grow fast enough by collisions of equal-sized bodies. There will be such collisions but I believe the growth is mainly through a large object sweeping up everything it encounters as the gas drifts inwards. The first calculations by Safranov had it taking at least a billion years to get to Neptune, (but the gas would have long gone.) Recent observations have shown massive planets that have grown withing 2 My, and no simulations can approach that rate of formation from equal-sized collisions.

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