“SOOT” PLANETS MAY BE MORE COMMON THAN WATER WORLDS IN SPACE

Scientists have discovered that many exoplanets once thought to be “water worlds” may actually be “soot” planets—carbon-rich worlds with methane atmospheres, similar to Saturn’s moon Titan. This new finding changes our understanding of the composition and potential habitability of worlds beyond our solar system.
An international team of astronomers has concluded that many exoplanets previously considered “water worlds” could in fact be “soot” planets—carbon-rich bodies with a composition similar to comets. The researchers published their findings on the arXiv portal.
The scientists analyzed the process of planet formation in protoplanetary disks and proposed a new concept: the “soot line.” This line is located closer to a star than the traditional “snow line,” beyond which icy planets form. In this inner region, carbon compounds are stable enough to be actively incorporated into the composition of forming planets.
According to the calculations, the “soot” content in such worlds could make up to 25% of their mass. As a result, they would have methane-rich atmospheres and hydrocarbon haze, making them resemble Saturn’s moon, Titan.
The authors of the study note that many “water worlds” may also contain a significant amount of carbon compounds. This means they should be classified into “dry” and “wet” variants. For example, among the known exoplanets, TOI-270 d could be a candidate for a “soot” world, as the James Webb Space Telescope has detected high levels of carbon dioxide and methane in its atmosphere.
The question of habitability on such planets remains open. On one hand, “soot” could suppress geological activity and strip a planet of its magnetic field. On the other hand, a methane-rich atmosphere and the presence of water could create conditions where pre-biological chemistry might emerge.