NASA’s James Webb Space Telescope (JWST) has confirmed a type of planet exists unlike anything in the solar system.

They’re dubbed a “Super-Venus” world, and one of these exoplanets – a planet which orbits another star from our Sun – is described in a paper published in Astrophysical Journal Letters.

Many of the more than 5,000 exoplanets so far discovered fall in a size range between Earth (radius of 6,378km) and Neptune (radius 24,766km). There is nothing which fills this size range in our own solar system. Astronomers have debated whether these exoplanets are rocky like Earth or icy planets like Neptune.

It has been assumed that, if these exoplanets are rocky, their atmospheres would be thick and hydrogen rich. If, however, they are icy, then their atmospheres should be water-rich leading them to be sometimes referred to as water worlds.

High, thick clouds have made it difficult to determine the atmospheric make up of these planets.

The new research focused on one of them: GJ 1214 b, which has a mass about 8.41 times that of Earth. It was discovered in 2009 and has a very tight orbit around its host star – a year on GJ 1214 b lasts just 1.6 Earth days.

GJ 1214 b is only 48 light-years from Earth, which is relatively close, making it one of the easiest of these intermediate planets to study.

The new analysis revealed an atmosphere which was unexpected. It was neither hydrogen-rich, nor water-rich. It was, instead, rich in carbon dioxide (CO₂).

GJ 1214 b, therefore, is neither a Super-Earth nor a Sub-Neptune, but a Super-Venus.

The atmosphere of Venus is 96% CO₂. It has thick clouds which help make the atmosphere extremely dense. The atmospheric pressure on Venus’s surface is 93 bar – about the same as 900m under water on Earth.

GJ 1214 b could be like a massive cousin of Venus.

“The detected CO₂ signal from the first study is tiny, and so it required careful statistical analysis to ensure that it is real,” explains co-lead author Kazumasa Ohno from the National Astronomical Observatory of Japan. “At the same time, we needed the physical and chemical insights to extract the true nature of GJ 1214 b’s atmosphere.”

The atmospheric signature is tiny. “It’s equivalent to Leo Tolstoy’s War and Peace,” Ohno says. “If I gave you 2 copies and changed 1 sentence in 1 of the books, could you find that sentence?”

Ohno led attempts to find theoretical models to explain the observations. They ran several “what if” scenarios to determine the makeup of the exoplanet’s atmosphere.

The model which best fit is that GJ 1214 b is a massive, inhospitable Venus-like world.

More observations will help confirm the team’s findings and work out how common super-Venuses are in the universe.