James Webb telescope discovers ancient 'water world' in nearby star system

A "mini-Neptune," the most frequent sort of planet outside of our solar system, was examined closely for the first time by the James Webb Space Telescope, which discovered evidence of water.

The exoplanet GJ 1214b, a mini-Neptune planet orbiting a star around 40 light-years from Earth, has now been seen through the clouds. Mini-Neptunes are a frequent sort of planet in our galaxy, resembling a scaled-down counterpart of the known gas giant; but, since there isn't one in our solar system, these worlds have mostly remained a source of scientific fascination.

Thick cloud cover prevented scientists from making previous views of the faraway planet, but the powerful James Webb Space Telescope's (JWST) infrared thermal vision allowed them to discover a fresh perspective through the mist. GJ 1214b possesses a steamy atmosphere, suggesting that it formerly existed as a potential "water world," according to the findings, which were reported on May 10 in the journal Nature(opens in new tab).

Rob Zellem, an exoplanet researcher at NASA's Jet Propulsion Lab, said in a statement that for over ten years, the only thing we actually knew about this planet was that its atmosphere was clouded or hazy. As the planet went through its orbit, the researchers utilized JWST's Mid-Infrared Instrument (MIRI) to map the planet's temperature. By collecting data on the planet's day and night sides, they were able to determine its composition.

On GJ 1214b, the temperature changed significantly from day to night, reaching a maximum of 535 degrees Fahrenheit (280 degrees Celsius) during the day and then dropping by more than 100 degrees F at night. A temperature differential of 100 degrees would be equivalent to a day on Earth with scorching heat during the day and a snowstorm overnight. This large temperature change on GJ 1214b suggests that the atmosphere of the planet must include more than simply light hydrogen molecules, such as water or methane. Given that the atmosphere differs from what the star is comprised of, scientists believe that this discovery offers an intriguing hint about the planet's past.

GJ 1214b "either lost a lot of hydrogen, if it started with a hydrogen-rich atmosphere, or it was formed from heavier elements to begin with — more icy, water-rich material," lead research author Eliza Kempton, an astronomer at the University of Maryland, said in a statement. "The simplest explanation, if you find a very water-rich planet, is that it formed farther away from the host star," she continued.

Although there is still plenty that astronomers don't know about GJ 1214b, they anticipate seeing additional mini-Neptunes with JWST soon. They want to determine a "consistent story" for how mini-Neptunes are made and how this specific one arrived there with so much water, according to Kempton.