Helium-dominated atmospheres on rocky planets provide unique climate conditions for potential life

Star system: LHS 1140 | Distance from the Sun: 48.8 light years

Climate models of rocky planets with helium-dominated atmospheres suggest these worlds may possess distinct thermal characteristics compared to planets with more common gases like nitrogen or hydrogen. Because helium is a simple atom with fewer internal ways to store energy, it creates a specific temperature profile that influences how heat is distributed and retained on a planet's surface.

The study compared the warming effects of helium to nitrogen and hydrogen atmospheres. While helium-dominated atmospheres provide more surface warming than nitrogen-rich ones, they are less efficient at trapping heat than hydrogen-dominated atmospheres. This temperature regulation directly impacts the habitable zone, the region around a star where liquid water can exist, making this zone narrower for planets orbiting red dwarf stars.

Researchers utilized radiative-convective modeling to simulate the physics of these alien atmospheres. They examined factors like how light interacts with gas particles and the pressure of the air, ranging from 1 to 20 times Earth's atmospheric pressure at the surface. By understanding these interactions, they assessed how these planets might look when analyzed from afar.

Despite the narrower habitable zone, these worlds are primary targets for future observation. Because helium-dominated atmospheres have a large scale height—meaning the atmosphere is more extended or "puffy" compared to those made of heavier gases like carbon dioxide—they are easier to detect and study using transit spectroscopy, a method where light from a star filters through a planet's atmosphere to reveal its chemical makeup.

Key findings
- Helium-dominated atmospheres provide more warming than nitrogen atmospheres but less than hydrogen atmospheres.
- Rocky planets with helium-dominated atmospheres around red dwarf stars have a narrower habitable zone than those with hydrogen.
- Large atmospheric scale height makes these planets excellent candidates for analysis by the James Webb Space Telescope.
- Helium's simple atomic structure leads to a steeper drop in temperature with altitude compared to more complex gas molecules.

Scientific study

Climates of temperate rocky planets with He-dominated atmospheres (external link)