Exoplanet the size of Neptune 90-light years from Earth could have water vapor, researchers suggest

A new Neptune-sized exoplanet with a ‘substantial atmosphere’ and the potential for water has been identified in deep space, according to a new study.

Known as TOI-1231 b, the exoplanet has a 24-day orbit around its star, TOI-1231, and could have an atmosphere similar to Neptune, given its size and density. 

There is also the potential for water vapor on the planet, which is 90 light-years from Earth, leaving scientists intrigued.

‘The low density of TOI-1231 b indicates that it is surrounded by a substantial atmosphere rather than being a rocky planet,’ said the study’s co-author, Diana Dragomir, an assistant professor in UNM’s Department of Physics and Astronomy, in a statement. ‘But the composition and extent of this atmosphere are unknown!’ 

Dragomir continued: ‘TOI-1231 b could have a large hydrogen or hydrogen-helium atmosphere, or a denser water vapor atmosphere. Each of these would point to a different origin, allowing astronomers to understand whether and how planets form differently around M dwarfs when compared to the planets around our Sun, for example.’

M dwarfs are types of stars that are significantly smaller than the Sun, ranging between eight percent and 50 percent of its mass.  They are the most abundant class of stars. 

The exoplanet has a 24-day orbit around its star and could have an atmosphere similar to Neptune, given its size and density. There is also the potential for water vapor on the planet, which is 90 light-years from Earth 

Water vapor on TOI-1231 b may be a possibility, but it is still one of the coolest exoplanets discovered, with an expected temperature of 140 degrees Fahrenheit.

Previous studies have suggested that planets with a temperature like this could have clouds high in the atmospheres, but further research into the exoplanet K2-18 b shows there is the potential for water in the atmosphere.

‘TOI-1231 b is one of the only other planets we know of in a similar size and temperature range, so future observations of this new planet will let us determine just how common (or rare) it is for water clouds to form around these temperate worlds,’ said the study’s lead author, Jennifer Burt.

The exoplanet was discovered by NASA’s Transiting Exoplanet Survey Satellite (TESS) and later confirmed with the Planet Finder Spectrograph (PFS) on the Magellan Clay telescope at Las Campanas Observatory in Chile.

Burt said the researchers were able to measure the radius and mass of the planet, which allowed them to theorize it’s similar to Neptune in its composition.   

‘Those values in turn allowed us to calculate the planet’s bulk density and hypothesize about what the planet is made out of,’ Burt explained. 

‘TOI-1231 b is pretty similar in size and density to Neptune, so we think it has a similarly large, gaseous atmosphere.’

Scientists hope to further examine the planet’s atmosphere with the Hubble Space Telescope and the James Webb Telescope, set to launch later this year. 

‘This new planet we’ve discovered is still weird – but it’s one step closer to being somewhat like our neighborhood planets,’ Burt continued. ‘Compared to most transiting planets detected thus far, which often have scorching temperatures in the many hundreds or thousands of degrees, TOI-1231 b is positively frigid.’  

The study is set to be published in The Astronomical Journal, but a pre-print version can be read here. 

Last month, NASA delayed the launch of the $10 billion Hubble replacement because the rocket to launch it is not yet ready, among other reasons.