K2-239 d is a rocky world located approximately 160 light-years away in the constellation Sextans. It is the outermost of three Earth-sized planets orbiting a very cool red dwarf star.

Key Physical Characteristics

• Planet Type: Terrestrial (rocky) world.
• Size: It is roughly 1.1 times the radius of Earth, making it very similar in size to our home planet.
• Orbit: It completes one orbit around its star every 10.1 Earth days.
• The Star: K2-239 is an M-dwarf star. Because it is much smaller and cooler than the Sun, its planets can orbit very closely and still remain temperate.

Habitability & Environment

In Lisa Kaltenegger’s research, K2-239 d is noted for its potential “Earth-like” radiation levels:

• Location: It sits within the Habitable Zone, specifically near the inner edge where liquid water could theoretically exist.
• Energy Intake: It receives a level of starlight that could support a temperate climate, depending on whether it has a protective atmosphere to regulate heat.
• Tidal Locking: Like most planets orbiting close to red dwarfs, it is likely tidally locked, meaning one side is in permanent daylight while the other is in eternal darkness.

Scientific Significance

• Ideal for Analysis: Because K2-239 is a relatively bright star for its type, it is considered an ideal target for transmission spectroscopy. This allows scientists to study the chemical makeup of the planet’s atmosphere as it passes in front of the star.
• Triple System: The system contains three planets (b, c, and d), all of which are Earth-sized. This provides a “laboratory” for Kaltenegger and her team to compare how three similar rocky worlds evolve differently at varying distances from the same sun.
• Rocky Composition: Its size and mass suggest a solid, rocky surface rather than a gas-shrouded “mini-Neptune,” which is a key requirement for the search for life.

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Published @ March 24, 2026 9:31 am