Daily Weird News Report
Some rocky exoplanets orbit so close to their stars that their surfaces may be covered in molten rock, yet they can still retain thick atmospheres for billions of years, according to a modeling study reported by Phys.org.
The apparent contradiction comes from the intense stellar radiation surrounding these worlds. Radiation should gradually drive atmospheric gases into space. But the new model suggests that lava moving across a planet’s surface can regulate the supply of gases from its interior, known as outgassing. On some planets, that release may balance the rate at which the atmosphere escapes.
The study, led by Stanford graduate student Barron Nguyen with researchers including Laura Schaefer, expands the “cosmic shoreline” framework. That framework describes a boundary between rocky planets able to keep atmospheres and those whose atmospheres are stripped away by stellar radiation.
The researchers propose a new region beyond that boundary called the “cosmic sandbar.” In this regime, hot, close-orbiting planets with molten surfaces can maintain atmospheres because outgassing and atmospheric loss remain in balance. The name refers to sandy ridges that form offshore on Earth.
Between the cosmic shoreline and the proposed sandbar lies what the researchers call the “airless valley.” Planets in that region may be close enough to their stars to lose atmospheric gases, but not hot enough to keep their surfaces molten and replenish those gases. As their surfaces cool and solidify, gases can become trapped underground.
To develop the model, the researchers simulated exchanges between an atmosphere and a molten surface while also accounting for atmospheric escape, cooling and the eventual solidification of lava. They compared the resulting lava-world scenarios with other known exoplanets and worlds in the solar system.
The work was motivated in part by observations of planets such as 55 Cancri e. The super-Earth, nearly eight times Earth’s mass, orbits about 20 times closer to its star than Mercury orbits the Sun. Phys.org reported that observations by the James Webb Space Telescope in 2024 indicated that 55 Cancri e has a thick atmosphere, adding to a growing list of similar lava worlds.
The researchers said future exoplanet surveys may further test and develop the expanded cosmic shoreline framework.
