NASA’s James Webb Space Telescope has discovered a giant Earth-like exoplanet located scores of light years away in a habitable zone known to harbor carbon-bearing molecules—meaning the planet may support life.
The space agency announced in a statement this week that a spectral analysis of K2-18 b—an exoplanet about eight times as massive as Earth located some 120 light years away—detected significant levels of carbon-bearing molecules including methane and carbon dioxide.
Astronomer Nikku Madhusudhan, lead author of the research and a scientist at the University of Cambridge, said that the new results show large quantities of methane and carbon dioxide in K2-18 b’s atmosphere without traces of ammonia, which supports the hypothesis that there may be a water ocean under a hydrogen-rich atmosphere.
“Our findings underscore the importance of considering diverse habitable environments in the search for life elsewhere,” Mr. Madhusudhan said. “Traditionally, the search for life on exoplanets has focused primarily on smaller rocky planets, but the larger Hycean worlds are significantly more conducive to atmospheric observations.”
NASA noted that the findings do not necessarily mean that K2-18 b can support life. The planet’s large size—a radius 2.6 times the radius of Earth—means that the planet’s interior likely contains a large mantle of high-pressure ice, similar to Neptune, but with a thinner hydrogen-rich atmosphere and an ocean surface.
Those so-called “Hycean worlds” are predicted to have liquid water or oceans—a vital ingredient for life. However, it is also possible that the ocean is too hot to be habitable.
“Our ultimate goal is the identification of life on a habitable exoplanet, which would transform our understanding of our place in the universe,” Mr. Madhusudhan said. “Our findings are a promising step towards a deeper understanding of Hycean worlds in this quest.”
Additionally, NASA’s observations also appear to have detected a molecule called dimethyl sulfide (DMS), the agency said. On Earth, DMS is primarily produced by organisms found in surface seawater as well as fresh water.
Mr. Madhusudhan told BBC News that his entire was ”shocked” when they saw the results, explaining DMS is “only produced by life” and the majority of the molecule in Earth’s atmosphere “is emitted from phytoplankton in marine environments.”
However, Mr. Madhusudhan noted that more data would be needed to confirm if DMS is indeed present. Those results are expected in a year.
“Upcoming Webb observations should be able to confirm if DMS is indeed present in the atmosphere of K2-18 b at significant levels,” he stated.
Many of the Earth-size exoplanets discovered in recent years orbit small red dwarf stars, rather than sun-like stars. These stars are much smaller and cooler than our sun and the exoplanets around them are in closer orbits than Earth is to the sun, but they likely have similar moderate surface temperatures because the stars are cooler.
K2-18 b is located in the constellation Leo and orbits the cool red dwarf star K2-18 in what’s known as the “habitable zone,” where the surface temperature of the planet could support liquid water and the potential for life.
Exoplanets such as K2-18 b, which have sizes between those of Earth and Neptune, are unlike anything in our own solar system, NASA said. These worlds are referred to as “sub-Neptunes” and are poorly understood among astronomers, who are actively debating the nature of these world’s atmospheres.
“Although this kind of planet does not exist in our solar system, sub-Neptunes are the most common type of planet known so far in the galaxy,” Dr. Subhajit Sarkar of Cardiff University in Wales, who is also a member of the analysis team, said in a statement. “We have obtained the most detailed spectrum of a habitable-zone sub-Neptune to date, and this allowed us to work out the molecules that exist in its atmosphere.”
NASA stated that data suggesting K2-18 b may be a Hycean exoplanet is intriguing to astronomers, as some believe that these worlds are promising environments to search for evidence for life on exoplanets.