Using the Webb telescope, scientists may have found the ‘best bet’ for an ocean world outside our solar system!

In humanity's relentless quest to find life beyond Earth, the key lies in discovering a world capable of hosting water. Excitingly, scientists may have pinpointed a planet beyond our solar system that harbours vast oceans of this life-sustaining liquid!

While thousands of exoplanets (worlds outside our solar system) have been identified so far, only a rare few lie within the ‘Goldilocks zone’—an area neither too hot, nor too cold, and thereby perfect to allow liquid water to exist. Among these, LHS 1140 b stands out.

Since its discovery in 2017, it has been subject to extensive examination. Located 48 light years (about 450 trillion kilometres) away from Earth, LHS 1140 b is relatively nearby in astronomical terms. This exoplanet is 1.7 times larger than Earth and boasts 5.6 times its mass.

Originally, scientists classified LHS 1140 b as a "mini-Neptune," a small gas giant with an atmosphere too thick in hydrogen and helium to support life. However, recent observations from the James Webb Space Telescope (JWST) have revealed a surprising truth: LHS 1140 b is a rocky "super-Earth," altering our understanding of its potential to support life.
The most promising ocean world candidate
The Webb telescope recently achieved a breakthrough by analysing the planet's atmosphere during its transit across its star. The absence of hydrogen and helium signatures led to the conclusion that the planet is not a mini-Neptune. Instead, the planet's density suggests it houses large quantities of water, as per study co-author Martin Turbet from France's CNRS research centre.

Lead study author Charles Cadieux, a PhD student at the University of Montreal, remarked that among all known temperate exoplanets, LHS 1140 b is possibly the most promising candidate for confirming liquid water on the surface of an alien world.

Approximately 10 to 20 percent of the exoplanet's mass is estimated to be water. In stark contrast, Earth's oceans account for a mere 0.02 percent of its mass. The state of this water, whether liquid or ice, hinges on the planet's atmospheric composition, with gases like carbon dioxide playing a crucial role.

One encouraging factor is the planet's gentle warming by its red dwarf star, which is only one-fifth the size of our Sun. This stellar relationship suggests that the exoplanet's surface temperature is likely comparable to that of Earth and Mars.

One hypothesis is that the planet's surface is predominantly ice, but with a substantial liquid ocean in areas most exposed to the star's heat. This ocean could span approximately 4,000 kilometres in diameter, covering about half the surface area of the Atlantic Ocean, according to models. Alternatively, the liquid water might be concealed beneath a thick ice shell, similar to the icy moons orbiting Jupiter and Saturn.

Webb's instruments have detected indications of “the presence of nitrogen,” Cadieux noted, emphasising that further research is required to confirm this finding. Nitrogen, ubiquitous on Earth, is considered another potential life-supporting ingredient.

The researchers aim to secure additional observation time with the Webb telescope to gather more data on LHS 1140 b. They estimate it will take at least a year to determine whether the exoplanet has an atmosphere, and an additional two to three years to detect the presence of carbon dioxide.

The study was recently published in The Astrophysical Journal Letters and can be accessed here.