Super-Earth Ocean World Discovered
JWST has identified LHS 1140 b as a likely "eyeball" ocean world 50 light-years away, with the 1.7x Earth-sized super-Earth containing 10-20% water by mass and a nitrogen atmosphere. The planet represents one of the most promising candidates for habitability outside our solar system.
- The host star, LHS 1140, is a red dwarf about a fifth the size of our sun and is located in the constellation Cetus. It is over 5 billion years old and has a slow rotation period of 131 days, making it relatively inactive and less likely to strip away the planet's atmosphere with powerful flares. - The "eyeball" configuration is a hypothesis based on the high likelihood that the planet is tidally locked, with one side permanently facing its star. This would create a stable "bulls-eye" of liquid water on the star-facing side, which models suggest could be 4,000 kilometers in diameter with a surface temperature of a comfortable 20°C (68°F). - While water covers over 70% of Earth's surface, it only accounts for 0.02% of our planet's mass. The estimate that LHS 1140 b is 10-20% water by mass illustrates how incredibly water-rich it is by comparison. - This planet was first discovered in 2017 by the MEarth Project, but its precise characteristics were uncertain. It took subsequent observations from the Hubble, Spitzer, and TESS space telescopes to refine its mass and radius before the JWST could analyze its atmosphere. - The potential for a nitrogen-dominated atmosphere is significant as it would be a "secondary atmosphere," one that developed after the planet formed, similar to Earth's. JWST's observations helped rule out the alternative scenario of it being a "mini-Neptune" with a thick, hydrogen-rich primary atmosphere. - LHS 1140 b orbits within its star's habitable zone, but receives only about 43% of the energy that Earth gets from the Sun. Its equilibrium temperature is a frigid
