Astronomers have made a thrilling discovery: LHS 1140 b, a distant rocky or icy exoplanet, might harbor a vast, temperate ocean, raising hopes of finding habitable worlds beyond our solar system. The so-called “Super Earth” is “our best bet” so far for finding liquid water on a planet beyond the solar system.

The exciting discovery made by the James Webb Space Telescope could mark a pivotal moment in our quest to find life among the stars.

Why LHS 1140 b Stands Out

LHS 1140 b orbits a red dwarf star 48 light-years away in the constellation Cetus. It is about 1.7 times the size of Earth. Its orbit is smack in the “habitable zone,” where conditions might be just right to support liquid water.

“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, lead author of the science paper and doctoral student at Université de Montréal.

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

LHS 1140 b has been of interest to planetary hunters for some time. Previous observations suggested it might be a water world, but it was the JWST’s advanced capabilities that provided crucial new insights.

It wasn’t clear whether LHS 1140 b was a mini-Neptune type exoplanet or a super-Earth (a rocky planet larger than Earth). James Webb’s data now strongly put the mini-Neptune scenario to rest. If LHS 1140 b is a mini-Neptune, you’d see strong absorption features due to its big atmosphere.

Instead, the evidence from James Webb’s spectroscopic data points to LHS 1140 b as a super-Earth. The data, in fact, goes a step further, revealing hints of a nitrogen-rich atmosphere like our planet’s — this particular feature requires more observation to confirm, the researchers note.

Nevertheless, the nitrogen atmosphere could be big if true as it greatly influences the conditions suitable for liquid water. Ryan MacDonald, a NASA Sagan Fellow at the University of Michigan noted that this is “the first time we have ever seen a hint of an atmosphere on a habitable zone rocky or ice-rich exoplanet.”

A promising start

Current models suggest that LHS 1140 b could resemble a snowball or ice planet, with one side always facing its star due to the exoplanet’s synchronous rotation (just like Earth’s Moon), resulting in a liquid ocean on the heated side. This ocean could span about 2,485 miles (4,000 kilometers) in diameter, or roughly the size of the Atlantic Ocean, with a surface temperature of around 20 degrees Celsius (68 degrees Fahrenheit).

While further observations are necessary to confirm these findings, the discovery of LHS 1140 b marks a significant milestone in the quest to find habitable worlds. As MacDonald aptly put it, “this is a very promising start.”

“This is our first tantalizing glimpse of an atmosphere on a super Earth in the habitable zone. Compared to other known habitable zone exoplanets, such as those in the TRAPPIST-1 system, the star LHS 1140 appears to be calmer and less active, making it significantly less challenging to disentangle LHS 1140 b’s atmosphere from stellar signals caused by starspots,” MacDonald said.

“Our initial reconnaissance of LHS 1140 b with JWST has revealed this to be perhaps the best habitable zone exoplanet currently known for atmospheric characterization. While we need more JWST observations to confirm the nitrogen-rich atmosphere, and to search for other gases, this is a very promising start.”

Scientists continue to study LHS 1140 b, hopeful that it will bring us closer to answering one of humanity’s most profound questions: Are we alone in the universe?

The findings were reported in the Astrophysical Journal Letters.