The thing is their density - it can be compared with cotton candy.
All three exoplanets are in the star system Kepler-51 in the constellation Cygnus. In size they are comparable with Jupiter and Saturn, their mass is hundreds of times less. Scientists called the new class “super-puff”.
Until recently, astronomers knew only about three types of planets: terrestrial, such as Earth and Mars, ice giants (Neptune) and gas giants (Jupiter). Perhaps the “super-puffs” represent a transitional phase of the planets - if so, then the Kepler-51 system will become a unique “laboratory" for testing scientific theories.
To understand the oddities of "cotton" exoplanets, scientists took several years. Presumably, all three giants are composed of hydrogen and helium, and also have a layer of methane around them. In composition, it is very similar to the atmosphere of Titan, one of the moons of Saturn.
Scientists reckon that the new James Webb Space Telescope will help to understand in more detail the composition of ultralight planets. Its launch is scheduled for March 30, 2021.