The exoplanet HAT-P-26b located at a distance of 437 light-years from us has a primitive atmosphere consisting almost entirely of hydrogen and helium. This conclusion was made by scientists, analyzing the data obtained by space telescopes Hubble and Spitzer.
The planet is comparable in size to Neptune. She is pretty close to her star. Scientists have found traces of water in its atmosphere. Observations were conducted when the planet passed before its star. The researchers also measured the level of metallicity of the planet, that is, the concentration of elements heavier than helium. It was only 5 times larger than that of the Sun. That is, the metallicity of HAT-P-26b is closer to Jupiter than to Neptune. For comparison, the metallicity of Jupiter is 2 to 5 times higher than the metallicity of the Sun, while for Neptune and Uranus this index is 100 times higher.
This is due to the fact that Neptune and Uranus were more heavily bombarded with ice fragments rich in heavy elements than Jupiter and Saturn, which formed in the warmer part of the disk.