This Neptune-Like Exoplanet May Have Water Clouds

Despite the possible presence of water vapor, TOI-1231 b is likely not habitable because of its size

Artist’s rendering of TOI-1231 b, a Neptune-like planet about 90 light-years away from Earth. The planet is colored a purple-blue hue with thin, wispy clouds in its atmosphere.
It’s considered one of the coldest and smallest exoplanets discovered so far. NASA/JPL-Caltech

Last week, an international group of scientists announced the discovery of a Neptune-like exoplanet 90 light-years away from Earth that might have water clouds. This discovery marks an exciting step in a new era exoplanet research, reports Sophie Lewis for CBS News.

The exoplanet, located outside of Earth’s solar system, is called TOI-1231 b. Both Neptune and TOI-1231 b hold a resemblance with one another with their gaseous states and rich atmospheres. This exoplanet orbits a red-dwarf star, NLTT 24399, every 24 Earth days. This red-dwarf star is smaller, dimmer and less dense than Earth’s sun, but it’s much older.

The exoplanet’s mass is 15.4 times larger than Earth. Despite closely orbiting its star, TOI-1231 b is colder than other exoplanets at an average 134 degrees Fahrenheit. It’s considered one of the coldest and smallest exoplanets discovered so far. TOI-1231 b is likely not habitable because of its size.

"Even though TOI-1231 b is eight times closer to its star than the Earth is to the Sun, its temperature is similar to that of Earth, thanks to its cooler and less bright host star," says study co-author Diana Dragomir, an exoplanetologist at the University of New Mexico, in a statement. "However, the planet itself is actually larger than Earth and a little bit smaller than Neptune—we could call it a sub-Neptune."

Cold planets occasionally have clouds high in their atmospheres. By comparing TOI-1231 with other exoplanets similar in size and temperature, scientists can infer whether water clouds are present or not.

"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," says the study’s lead author Jennifer Burt, a NASA JPL scientist, in a statement.

To spot the exoplanet, scientists used data from the Transiting Exoplanet Survey Satellite (TESS). Launched in 2018, TESS studies 200,000 of the brightest stars near the sun. The satellite searches for exoplanets by identifying “transits,” which occur when a planet blocks light from the star it’s orbiting.

Scientists conducted further research using the Planet Finder Spectrograph (PFS) with the Magellan Clay telescope at Las Campanas Observatory in Chile. PFS searches for exoplanets based on gravitational interaction with host stars to learn more about their mass and orbit. This measurement is obtained by identifying variations in stellar velocity.

Later this month, the Hubble Space Telescope is set to get a closer look at TOI-1231 b. Hubble will study hydrogen escaping from the exoplanet's atmosphere. These atoms are hard to spot because they are usually blocked by our own planet’s atmosphere or interstellar gas. If the James Webb Telescope launch this fall is not delayed, it will also further investigate exoplanets and the composition of their atmospheres.

With the Hubble and Webb telescopes, Scientists will be able to use transmission spectroscopy to capture starlight emitted from TOI-1231 b through its atmosphere. When the molecules in the atmosphere absorb the light, they show up as dark lines that can be read as a “bar-code” and inform scientists about gases in the atmosphere.

“One of the most intriguing results of the last two decades of exoplanet science is that, thus far, none of the new planetary systems we've discovered look anything like our own solar system," Burt says in a statement.

Further information about their findings will also be published in an upcoming issue of The Astronomical Journal.

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