A planet relatively close to Earth may be the first planet discovered outside our solar system to have a potentially habitable liquid ocean, according to scientists using the James Webb Space Telescope. More than 5,000 planets have been discovered outside the solar system so far, but only a few are in the so-called “Goldilocks zone” (not too hot, not too cold) where liquid water, a key ingredient for life, could exist.

The exoplanet LHS 1140 b is one of the few planets in this habitable zone and has been extensively studied since its discovery in 2017. It is 48 light-years from Earth, which corresponds to a distance of more than 450 trillion kilometers (280 trillion miles) – relatively close in the vast distances of space.

The exoplanet was thought to be a small gas giant called a “mini-Neptune” with an atmosphere too full of hydrogen and helium to support alien life. But new observations by the Webb telescope have confirmed that the exoplanet is actually a rocky “super-Earth.” It is 1.7 times the size of Earth but 5.6 times its mass, according to the study, published Wednesday evening in The Astrophysical Journal Letters.

The “best option” for the ocean world

The Webb telescope was able to analyse the planet’s atmosphere as it passed in front of its star. There were no signs of hydrogen or helium, ruling out the planet being a mini-Neptune. The planet’s density suggests “it actually has a lot of water”, study co-author Martin Turbet of France’s CNRS research centre told AFP.

There could be a very large amount of water indeed. The total amount of water in Earth’s oceans is only 0.02 percent of its mass. But the exoplanet is estimated to be 10 to 20 percent water. Whether that water is liquid or frozen depends on the planet’s atmosphere.

“We don’t have direct evidence that it has an atmosphere, but several elements point to it,” Turbet said.

The study’s lead author, Charles Cadier, a graduate student at the University of Montreal, said: “Of all the temperate exoplanets currently known, LHS 1140 b may one day be our best chance for indirect confirmation of liquid water on the surface of an alien world.”

One positive aspect is that the planet is slightly warmed by a red dwarf star that is one-fifth the size of the Sun. The exoplanet’s surface temperature should be roughly similar to Earth and Mars, Turbet said. The presence of gases such as carbon dioxide will play a key role in determining whether a planet is covered in ice or water.

Apple Ocean

One possibility is that the surface is mostly ice, but there is a vast liquid ocean where the planet is most exposed to the heat of its star. Simulations suggest this ocean could be about 4,000 kilometers (2,500 miles) in diameter, roughly half the surface area of ​​the Atlantic Ocean.

Or liquid water could be hidden beneath a thick crust of ice, as is the case with the moons Ganymede, Enceladus or Europa orbiting Jupiter and Saturn. Webb’s instrument found signs of “the presence of nitrogen,” Cadier said, adding that more research is needed to confirm the discovery. Nitrogen is found everywhere on Earth and is thought to be another potential ingredient for life.

Researchers hope to use the valuable Webb telescope for a few more hours to learn more about LHS 1140 b. It will take at least a year to confirm whether the exoplanet has an atmosphere, and another two to three years to detect the presence of carbon dioxide, the researchers say.