A famous "unknowable fact" of early science was the composition of the sun; but Bunsen and Kirchhof's discovery of the techniques of spectroscopy enabled Janssen to show in 1868 that an unknown substance was present in the solar spectrum. In 1869, the astronomer royal, Sir Norman Lockyer, finding the same bright yellow lines, christened the unknown substance helium, the metal from which the sun was made, but of which no traces could be found on earth. It wasn't until 1895 that Ramsay found He on earth when he was asked to investigate a gas, thought to be nitrogen, that was given off when uranium ore was heated. Ramsay was expecting to find a compound of argon, but the gas turned out to be totally new, so he called it "neon", but it turned out to have the same bright yellow line of Lockyer's "helium" proving that the supposed sun metal was actually a gas. (By 1898, Ramsay had found another inert gas in the atmosphere, so he got to call something neon anyway). Trying to figure out how a mixture of hydrogen and a totally inert gas fueled the sun was another exciting scientific project.

Moral: don't waste time on answers, study problems.