TRAPPIST-1 g is the sixth planet from its star and the largest of the four habitable-zone planets in the system, located 40 light-years away.
Key Physical Characteristics
- Planet Type: Terrestrial (rocky) world.
- Mass: It is slightly larger than Earth, with a mass of about 1.32 times that of our planet.
- Orbit: It completes one orbit around its dim red dwarf star every 12.4 Earth days.
- Size: Its radius is about 1.13 times that of Earth.
Habitability & Environment
In Lisa Kaltenegger’s research, TRAPPIST-1 g is often modeled as a “cold Earth” or an “Ice World”:
- Energy Intake: it receives only about 25% of the starlight that Earth gets from the Sun. This puts it at the very outer edge of the habitable zone.
- Atmospheric Needs: To remain habitable for liquid water, it would require a very thick atmosphere with a massive greenhouse effect—much stronger than Earth’s—to keep it from freezing solid.
- Composition: Like planet “f,” its lower density suggests it contains significant amounts of volatile materials, likely meaning it has a deep layer of water-ice or a global ocean covered by a thick ice shell.
Scientific Significance
- Testing the Limits: Planet “g” is a vital case study for the “outer edge” of habitability. It helps scientists like Kaltenegger determine exactly how much greenhouse warming is needed to prevent a planet from becoming a permanent “snowball.”
- Tidal Locking: It is tidally locked, meaning the star-facing side might have a small open-water area (a “liquid eye”) while the rest of the planet remains frozen in eternal darkness.
- Observation Target: Due to its larger size and position, it is a primary candidate for telescopes to look for heavy gases and determine if it has successfully held onto a substantial atmosphere.
