How long ago did scientists determine that the gas giant planets were gaseous?

I seem to recall a number of the sci-fi stories of the 40s, for example, there would be a base or colony on the surface of some place like Jupiter. Seems like “Who Goes There?” (the basis for two “The Thing” movies) might have even been on Jupiter. I even recall on “The Jetsons,” that they were on Jupiter one day, and someone made a comment about how short the days were.

Was this well-known to the scientific community as far back as the 1940s, and the sci-fi writers just didn’t get the memo?

Fascinating question—I had to go look this up! The reference I grabbed was Planets and Satellites, edited by Kuiper (yes, that Kuiper) and Middlehurst, Chicago Press, Chicago, 1961.

You can easily find the densities of the gas giants if you measure the size of the planet in an image in your telescope, and know its distance, which was known from the 19th century. Interpreting what these densities mean for the interior is a difficult task (and the details are still being worked out.) You can imagine many different configurations: a planet of roughly constant density throughought, or one with many layers of different densities.

An astronomer named Jefferies in 1923 pointed out that the interiors of the gas giants cannot be gaseous like stars (which have similar composition) because the planets are not hot enough, and calculated that the interior of the planet must be solid. This lead him to calculate a density at the “surface” of much less than the density of water—but he said that this result was not to be taken seriously, because it was much too low for a solid surface. He suggested that the planets must have a solid core with a vast, tenuous atmosphere.

In 1924, a Russian astronomer named Fessenkov noted that the surface density of Jupiter must be lower than any solid, and any liquid—except for hydrogen and helium.

In the 1930’s, more sophisticated models were developed that approach our modern model of Jupiter, with a dense core (metals and silicates) surrounded by a more dense layer (their model: high-pressure ice, ours: metallic hydrogen), then molecular hydrogen.

So a colony “on” Jupiter would have been an anachronism in the 40’s.

Even if they didn’t have a good model of the planet’s interior and surface, couldn’t they have computed a reasonably accurate number for its surface gravity? That would seem to make any surface base very improbable, unless they brought along a magic anti-gravity device.

Actually, “Who Goes There?” was set in Antarctica, near the magnetic pole. The Thing wouldn’t have been nearly as much of a threat on some other planet; the fear was that it would take over the Earth. The most prominent surface-of-Jupiter story I can recall would be Asimov’s “Not Final!”, and its sequel “Victory Unintentional”.

And I should point out that to determine the density of the planets, you also need to know their masses. Fortunately, though, the gas giants all have moons, which makes it easy to determine their masses.

Also, in Who goes there, the thing is described as being from ‘beyond the stars, from a planet with a hotter, bluer sun’.

OK, so it wasn’t “Who Goes There?” However, the story I’m thinking of mentions that the weather is so cold that “tools can actually be made of ice.” (My paraphrase). If that reference is in “Who Goes There?,” then I’ve misplaced the setting. If it was in another story in that collection, I’ve misplaced the title.

Indeed. Good catch.

Yeah, the gravitational acceleration at Jupiter’s cloudtops only depends on the mass and radius. It’s like 2 1/2 gees.

I think Podkayne’s answer is close - and I agree that it’s a fascinating question - but I suspect that the uncertainty, particularly in popular accounts, persisted for a bit longer.

To flesh out Podkayne account of the background, several things about Jupiter had become clear by about 1800. From much earlier, people had realised that different visible features were rotating round the planet at different speeds. Thus long before that date, the consensus was that what we were seeing through telescopes were cloud tops. Therefore, it was obvious that the atmosphere on Jupiter had to be reasonably substantial and certainly opaque. The next stage was that Bessel realised that the average density of the planet had to be substantially less than that of the Earth (via the measurement indicated by Podkayne, plus a few others). The average density of the Earth itself was also sort of known at this time.
By way of comparison, it wasn’t even obvious at this time that the Sun was gaseous. Herschel thought it was mainly solid and even inhabited. He also thought that Jupiter was mainly solid with a thin atmosphere, a view also put forward by David Brewster later in the 19th century. This was the concensus opinion about the planet for a good long time. Some others did disagree, arguing that the planet was very, very hot. 18th century exponents of this were Buffon and Kant, but you also find James Nasmyth arguing the same in 1853.
The big late-19th century observational controversy about the interior of Jupiter was then whether there was a source of energy. Some, in retrospect rather primitive, measurements suggested that the planet was radiating significantly more energy than it was receiving from the Sun. Which would suggest that the planet was hot. This wasn’t too difficult to explain, given that in the same period you also had the Helmholtz-Kelvin hypothesis that the heat of the Sun was due to its gravitational contraction. (Oddly enough, the current view is that Jupiter does give off a very. very slight excess of energy - much less than that considered in the 1800s - and that this is probably due to contraction after all.)
I could conceive of people doing serious models of Jupiter’s interior in the late-1800s, to parallel those for the Earth and the Sun. (Indeed, I begin to wonder why nobody did propose any at that time.) The crucial shift would seem to be the renewed interest in such models, particularly for stars, in roughly the 1920s. It’s Eddington’s work on stellar structure that presumably prompted Jeffreys’ model in 1923. That’s Sir Harold Jeffreys, by the way. Yet even though his model had a significant enough atmosphere, it was still only 6000 km deep, compared to a planetary radius of about 70,000 km.
The few examples I know of from the decades immediately following are much the same: big atmospheres, but still mainly a solid core. Rupert Wildt proposed a model in 1934 where the atmosphere was about 13,000 km deep, while even as late as 1951 both Ramsey and DeMarcus suggested that the atmosphere was of neglible depth.
I suspect that the current firm conclusion that the planet is virtually all atmosphere, with only a small solid core, is ultimately a product of the spacecraft mission era.

There’s also the lag with respect to popular understanding to consider. For instance, I happen to have a copy of Sir James Jeans’s Through Space and Time (Cambridge, 1934), his Royal Institution Christmas Lectures from 1933, to hand. As is typical for this sort of popular astronomy book from the period, he devotes an entire chapter to an account of the planets. From the point of view of the current question, what’s striking is that he ducks it entirely. He discusses Jupiter at some length, but just completely avoids the question of what’s beneath the clouds. And this is Jeans, most of whose research was in the same tradition as Jeffreys. He must have been aware of the recent models, yet he seems to regard the entire topic as unsuitable for a popular audience. Any non-specialist looking for guidence in the 1940s might reasonably have turned to Jeans and concluded from the book that nothing was known about the issue.

What’s the sci-fi story where they’re building a “bridge” on Jupiter? Not really a bridge, but that’s what the protagonists call it. By Dick, perhaps, or Blish?

FWIW, the prologue to the 1950’s version of War of the Worlds (where Cedric Hardwicke narrates as the Martian’s ponder the choices for conquest) Saturn is depicted with a solid surface.

That would be the first section of “Cities in Flight”, by Blish.

The bridge being to test gravitational stresses and help design the “spindizzy” that allows the cities to leave the earth in the 2nd section.

OK, just bumping this to correct my conflation of stories. The story I was referencing above was actually ‘Call Me Joe’ by Poul Anderson (1957), which I had conflated with an icy story with a three word title written by a ‘Joe,’ ‘Who Goes There?’ by Joseph Campbell Jr (1938). So Anderson was behind the times, not Campbell.

That’s John W. Campbell Jr.

Joseph Campbell is the myth guy.’s-adventure-audio

Yeah, when Joseph Campbell talks about Jupiter being gassy, that’s a whole different conversation. :smiley:

Just thinking - didn’t Clark do a short story set in the atmosphere of Jupiter, with a bionic human who was going to explore deep in the clouds?

A novella. A Meeting with Medusa

That’s it! Thanks.

One of Cliff Simak’s best stories, “Desertion” also takes place on Jupiter, with acknowledgement that humans couldn’t live there, but still expecting a surface that suitable aliens could live on.

Might as well add Asimov’s 1941 Not Final! and its 1942 sequel Victory Unintentional to the list of SF with advanced jovian critters on a surface of the planet.