Keep an eye on this one: astronomers find a potentially habitable ice world

An exoplanet called LHS 1140 b could be the closest habitable world to Earth, an analysis of data collected by the James Webb Space Telescope (JWST) has shown.

Located 48 light-years away in the constellation Cetus, LHS 1140 b is one of the most promising exoplanets found in another star’s habitable zone, according to the study led by a team of astronomers from Université de Montréal (UdeM) in Canada.

The planet is 1.7 times the size of Earth and is located in the so-called “Goldilocks’ Zone” of the low-mass red dwarf star it orbits. Exoplanets in this zone have temperatures that could allow water to exist on them in liquid form.

According to researchers, LHS 1140 b is either completely covered in ice – similar to Jupiter’s moon Europa – or maybe an ice world with a “bull’s eye” of a liquid ocean and a stable, cloudy atmosphere.

The ocean is believed to measure about 4,000 kilometers in diameter, equivalent to half of the surface area of the Atlantic Ocean.

The surface temperature in the middle of this alien ocean could even be a pleasant 20 degrees Celsius, all of which suggests that the planet is a promising “super-Earth,” according to researchers.

“Of all currently known temperate exoplanets, LHS 1140 b could well be our best bet to one day indirectly confirm liquid water on the surface of an alien world beyond our Solar System,” said Charles Cadieux, a Ph.D. student at UdeM and lead author of the study.

“This would be a major milestone in the search for potentially habitable exoplanets,” Cadieux said.

From 'mini-Neptune' to 'super-Earth'

When the planet was first discovered, astronomers speculated it might be a gaseous “mini-Neptune.” However, the analysis of data from the JWST collected in December 2023 “strongly” excluded that scenario, researchers said.

The new evidence suggested that LHS 1140 b might not only have liquid water but also a nitrogen-rich secondary atmosphere that came to be after the world initially formed.

“This is the first time we have ever seen a hint of an atmosphere on a habitable zone rocky or ice-rich exoplanet,” said Ryan MacDonald, an astronomer from the University of Michigan who contributed to the research.

“LHS 1140 b is one of the best small exoplanets in the habitable zone capable of supporting a thick atmosphere, and we might just have found evidence of air on this world,” MacDonald said.

More data and time are needed to confirm the findings, according to UdeM professor René Doyon, who supervised the study. More specifically, researchers will need at least a year of observations to verify that LHS 1140 b has an atmosphere and up to three years more to detect carbon dioxide.

“Detecting an Earth-like atmosphere on a temperate planet is pushing Webb’s capabilities to its limits – it’s feasible, we just need lots of observing time,” said Doyon.

Due to its limited visibility with the JWST, the planet can only be observed at a maximum of eight times per year. It means that the telescope will have to observe it “at every possible opportunity” for several years to determine whether it has habitable surface conditions.

The results of the study are available on arXiv, an open-access research platform, and will soon be published in The Astrophysical Journal Letters, a peer-reviewed publication.