Thick carbon dioxide or sulfur dioxide atmospheres possible on lava planet TOI-561 b

Star system: TOI 561 | Distance from the Sun: 276 light years

TOI-561 b is a rocky, ultrashort-period exoplanet that orbits its star extremely quickly, resulting in intense irradiation. Recent data suggests this world may possess a thick, secondary atmosphere hovering above a global, molten surface, or magma ocean. Unlike the primary atmospheres of giant planets, which are captured from gas clouds, a secondary atmosphere is generated by gases released from the planet's interior over time.

Researchers used the PROTEUS framework, a computer model that links a planet's interior processes with its atmospheric evolution, to simulate how TOI-561 b could maintain such an atmosphere for billions of years. By testing various chemical compositions and physical conditions, the model identified the specific requirements necessary for the planet to hold onto its gas against the eroding effects of stellar radiation.

The findings show that TOI-561 b is consistent with having a high-pressure atmosphere reaching up to 10,000 times the pressure found at Earth's surface. This thick layer is likely composed of heavy molecules, dominated by either carbon dioxide or sulfur dioxide. Successful scenarios require an oxidized mantle and an efficient mechanism for retaining gases, suggesting that interior-atmosphere interactions are critical for the survival of atmospheres on irradiated rocky worlds.

Key findings
- TOI-561 b likely hosts a thick, high-molecular-weight atmosphere of 10^3 to 10^4 bar pressure.
- Atmospheric composition is likely dominated by either carbon dioxide or sulfur dioxide.
- Survival of this atmosphere requires an oxidized mantle and a small iron core radius fraction.
- A global magma ocean is consistent with the observed bulk density of the planet.
- Retention of these gases is possible despite intense irradiation if escape efficiency remains low.

Scientific study

Evolutionary pathways toward survival of a thick CO2- or SO2-rich atmosphere on the lava world TOI-561 b (external link)