The astronomical community generally believes that one of the most common types of planets in the Milky Way is a "water world", which is speculated to be rich in water or ice. However, the latest research by Jie Li's team at the University of Michigan shows that some planets are low-density and can easily be misjudged as rich in water. In fact, their main components may be pistil-like organic matter rich in carbon, hydrogen, oxygen, and nitrogen. Scientists estimate that "soot" accounts for up to 40% of the comet's total mass.
An artist's depiction of the "Smoke Planet" and its formation. Image source: Ari Gea/SayoStudio
The study points out that, similar to the snow line (the distance at which water ice can stably exist around a star), there is also a "soot line" in the planet-forming disk, which refers to the location where this organic matter can stably persist. In the middle area between the soot line and the snow line, it is suitable to form a planet rich in soot but lacking in water; outside the snow line, water and soot are mainly mixed, forming a "soy-water world". Models estimate that these sour-dominated planets may contain up to 25% sor, while "soon-water" worlds may have 15-20% sor and anywhere from 25% to 50% water.
It is extremely difficult to distinguish between the "smoke world" and the "water world". Existing planet mass and radius data cannot distinguish the two types of planets, leading to the fact that many originally thought to be "mini-Neptunes" may actually be composed of organic carbon rather than water. The authors suggest that only by analyzing the composition of a planet's atmosphere can we accurately determine which type of planet it belongs to.
Observations show that methane and carbon dioxide have been detected in the atmospheres of some exoplanets such as K2-12b and TOI-280d, supporting that they belong to a "soot world" or have experienced migration from the outside to the inside. In particular, TOI-280d has an unusually high carbon-to-oxygen ratio, which is closer to the theoretical definition of a "solar planet".
Scientists point out that soot planets have unique implications in terms of habitability: they may have diamond cores, which cause slow circulation of volatiles and make it difficult to generate a magnetic field to protect life. However, they are also rich in organic matter such as methane, which provides raw materials for the prebiotic chemical processes required to originate life.
The paper concludes that more detailed atmospheric observations and theoretical modeling are needed to clarify the boundary between the water world and the soot world.
Compiled from /ScitechDaily