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For context, at some point during the 20th century (and maybe earlier as well), the most popular planet formation theory and the one that was taught at (at least some) schools was the theory that the planets were somehow ‘spit out’ by the sun.

I am not very familiar with this theory, and I have only ever heard it from older people (never less than 60) who were taught this during their childhood education.

Obviously in modern day this is not the prevailing planetary formation theory, so my question is, at what point was this idea phased out of public education?

Note: I know this was a process, and so a 10 year range of time or a decade is an acceptable answer, or the date of a seminal finding that begun the process. Also if you personally have more information about this but maybe not a definitive answer, I would still love to hear about it in the comments or an answer (e.g. I don’t even know what this theory was called)

Justin T
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    A better question would be asking what evidence does disprove the idea. As it is, this seems more suited to History of Science. – ProfRob May 31 '22 at 20:32
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    @ProfRob I didn’t realize that was a SE, thanks for pointing that out! – Justin T Jun 01 '22 at 02:36
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    There's a large collection of old formation hypotheses at https://en.wikipedia.org/wiki/History_of_Solar_System_formation_and_evolution_hypotheses – PM 2Ring Jun 01 '22 at 03:51
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    I suppose that the closest match is "In 1951, 1962, and 1981, Swiss astronomer Louis Jacot [...] maintained that planets were expelled, one at a time, from the Sun, specifically from an equatorial bulge caused by rotation". Most of the old pop-sci books I read in the mid 20th century favoured some variation of the planetary material being pulled from the Sun by a tidal interaction with a passing star, and that was mentioned in sci-fi too. But it wouldn't surprise me if there were a much older "spitting out" theory, either scientific or from "folk" cosmology. – PM 2Ring Jun 01 '22 at 04:31
  • @PM2Ring That Louis Jacot idea is exactly what I have been hearing about; thanks a ton! – Justin T Jun 01 '22 at 04:44
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    Anecdotally, I was in my teens in the 80's and I remember diagrams of blobs being pulled out of the sun. I'm unsure if it was in an actual textbook or just an older book out of the library though. – Michael Richardson Jun 01 '22 at 15:31

3 Answers3

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That specific idea doesn't seem familiar to me, and I work in that field. Particularly this idea would only be called 'theory' when making testable predictions.

The only thing that comes to mind here is Laplace's extended solar atmosphere. Laplace (in the leate 1700's), as one of the first, invoked the centrifugal force in order to hypothesize a disc forming from an extended solar atmosphere, which would then destabilize into rings, forming the seed masses for planets as we see them today.

Then, for a long time only small progress was made with many names and minuscule contributions, until Safranov's book on "Evolution of the protoplanetary cloud and formation of the Earth and the planets" came out in 1962 in the USSR.
There, Safranov already claims the Laplacian idea to be disproven (presumably as differences in composition between the sun and the planets became recognized) and that "Nowadays it is generally accepted that the planets were formed from material rotating about the sun in the form of an extended gas-dust cloud" and that "the problem of the origin of the cloud itself has not been solved". Ideas of accreting the protosolar nebula via Bondi&Hoyle accretion (cited as 1944, I guess most modern authors cite their later work..) are already recognized.

I was just rereading the introduction to aforementioned book, and it seems to me that "sun spitting out planets" is nowhere to be found, and could have been a broad oversimplificiation in the public eye and school books of the Laplacian idea.

AtmosphericPrisonEscape
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    Sounds like Louis Jacot's "solar fission" ideas, and Tom Van Flandern's variations. They were never particularly popular though, at least not among scientists. – Christopher James Huff May 31 '22 at 22:52
  • I think it might even be an older idea than Laplace. When reading up on Comte de Buffon's experiments with cooling spheres to determine the age of the Earth, it looked like he was basing the project on an idea of solar ejection proposed by Newton. I do not know the Newton source, though. – Anders Sandberg Jun 01 '22 at 08:34
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Between 1965 and 1980

I recall a book from the "Ladybird" series of short non-fiction books for children which included two possibilities for the formation of the planets. One was "there was left-over gas in a nebula around the sun, this eventually formed planets" and the other was "A passing star tidally pulled matter from the sun into space, forming the planets".

I believe the book was "The Ladybird book of the Night Sky", first published in 1965, but I would have read a version in about 1980.

James K
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    Fascinating! Thanks for giving some literature that corresponds to this idea! – Justin T Jun 01 '22 at 02:38
  • The concept apparently dates back to 1918: "The tidal theory, proposed by James Jeans and Harold Jeffreys in 1918, is a variation of the planetesimal concept: it suggests that a huge tidal wave, raised on the sun by a passing star, was drawn into a long filament and became detached from the principal mass. As the stream of gaseous material condensed, it separated into masses of various sizes, which, by further condensation, took the form of the planets." https://www.infoplease.com/encyclopedia/science/space/astronomy/solar-system/origin-of-the-solar-system – towe Jun 02 '22 at 13:18
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Spit out? In 1955 my parents gave me an illustrated book on Astronomy, which gave two hypotheses: the Kant-Laplace (nebular) hypothesis, and Sir James Jeans' idea that a passing star pulled some material out of the Sun, which condensed to form planets. I think that Kant-Laplace was perceived as having problems with angular momentum. I came across this indirectly, in one of Fred Hoyle's books (where he argued that the angular momentum problem wasn't real).

The two stars idea was certainly around in the popular imagination in the 40s and 50s, as E.E. Smith alludes to it in the Lensman series. Smith wanted lots of suns with planets, so the two stars idea was a big problem. His solution was to make two galaxies collide to give him the collisions (and plants) he needed.

BTW, it seems to me that there are just too many exoplanets for "two stars" to be viable.

Simon Crase
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    Smith wrote the magazine verisons of the Lensman series in the 1930s. Presumably that include Gray Lensman where KInneson used the theory to deduce that Boskone must come from the galaxy which collided with ours billions of years earlier. I suppose someone could look up its publication in Astounding in 1939 to check if they wanted to. – M. A. Golding Jun 01 '22 at 17:28
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    The idea that planets were formed when two stars passed closed together has been obsolete for many decades. – M. A. Golding Jun 01 '22 at 17:34