Astronomers have identified a unique multi-planet system, K2-360, featuring an ultra-dense “super-Earth” and an outer planetary companion. This discovery, published in Scientific Reports on November 8, offers fresh insights into planetary formation and evolution in extreme conditions.
Details of the K2-360 System
Located approximately 750 light-years away, the K2-360 system includes two planets orbiting a sun-like star:
- K2-360 b:
- An ultra-short period super-Earth orbiting its star every 21 hours.
- Measures 1.6 times Earth’s size but has a mass of 7.7 Earth masses, making it as dense as lead—the densest known ultra-short-period planet.
- Likely represents the exposed iron-rich core of a once-larger planet, stripped of its outer layers by intense stellar radiation.
- K2-360 c:
- An outer planet with a mass at least 15 times that of Earth, completing an orbit every 9.8 days.
- Does not transit its star, but its gravitational influence allowed researchers to measure its minimum mass.
Key Findings
- Formation Insights:
- The extreme density of K2-360 b suggests it underwent high-eccentricity migration, where interactions with K2-360 c caused the inner planet’s orbit to become elliptical before tidal forces circularized it.
- This process stripped K2-360 b of its gaseous envelope, leaving behind a rocky core with an iron content similar to Earth but more extreme.
- Surface Conditions:
- K2-360 b’s proximity to its star likely keeps its surface in a molten, magma state, due to extreme heat.
- Unique Architecture:
- Systems with both an ultra-short-period planet and a massive outer companion are rare. K2-360’s structure provides a valuable case study for testing theories of planet migration and composition.
Significance of the Discovery
- Extreme Planetary Evolution: K2-360 b’s high density and compact orbit make it an ideal model for studying how planets evolve under intense radiation and gravitational forces.
- Constraining Models: The system challenges existing models of planetary migration, suggesting alternative pathways for planets to settle into ultra-short-period orbits.
- Comparative Planetology: Understanding K2-360 b offers broader insights into the diversity of rocky planets across the galaxy, particularly those subject to extreme environments.
By uncovering this dense super-Earth and its massive outer companion, astronomers have gained a new perspective on how planetary systems form and adapt to their surroundings, deepening our understanding of the varied architectures that exist in the cosmos.