The new planets, which are believed to have an extremely low density, have been branded “super-puffs”. Three were discovered by NASA’s Kepler space telescope in 2014.
Less than 15 have been identified in our galaxy in total.
However they were only designated as a new type of planet by NASA on Thursday.
This followed a study by scientists at the University of Colorado Boulder that is due to be published in The Astronomical Journal.
The planets are almost as large as Jupiter, the largest planet in our super system, but have 100 times less mass.
They have a density of 0.1 grams per cubic centimetres of volume, very similar to that of candy floss.
On the University of Colorado Boulder website Zachory Berta-Thompson, who coauthored the study, commented: “This is an extreme example of what’s so cool about exoplanets in general.
“They give us an opportunity to study worlds that are very different than ours, but they also place the planets in our own solar system into a larger context.
“We knew they were low density.
READ MORE: NASA launch fails as Starliner ‘has not reached the orbit required’
Ms Libby-Roberts explained: “It definitely sent us scrambling to come up with what could be going on here.
“We expected to find water, but we couldn’t observe the signatures of any molecule.”
This led to suspicion the planets could be surrounded by methane or salt crystals, which would explain the infrared light reaction.
In the Milky Way Titan, a moon of Saturn, is known to be surrounded by methane.
Ms Libby-Roberts continued: “If you hit methane with ultraviolet light, it will form a haze.
“It’s Titan in a nutshell.”
Separately on Friday Boeing’s Starliner capsule ran into trouble as it attempted its first test flight.
Shortly after blasting off problems were reported with the rocket which is due to undertake a planned flight with astronauts on board next year.
The Atlas V rocket left its destination in Florida safely just before sunrise, headed for the International Space Station.
However, the rocket fell into trouble just half an hour into its journey when Boeing reported that the capsule’s insertion into orbit was not normal.