The Planet That Defies Physics: What’s Hiding Inside K2-360 b?
An international team of researchers from Japan and Europe has unveiled a groundbreaking discovery: a dense “super-Earth” planet in the K2-360 system, located approximately 750 light-years from Earth. Published in Scientific Reports on November 8, this finding sheds new light on how planets form and evolve in extreme environments.
K2-360 b: The Ultra-Short Period Super-Earth with Extreme Density
The standout of this system, K2-360 b, is a rocky planet about 1.6 times the size of Earth, completing an orbit around its sun-like star every 21 hours. Its extreme density—comparable to lead—makes it one of the densest ultra-short period planets discovered to date.
Mass and Size:
Mass: 7.7 times that of Earth
Diameter: Slightly larger than Earth
Density: The planet’s density suggests it might be the stripped core of a once-larger planet that lost its outer layers to intense stellar radiation.
“This is the densest well-characterized planet among ultra-short period planets,” said John Livingston, lead author of the study.
K2-360 c: The Massive Outer Companion Shaping the System
K2-360 c, the system’s other planet, is at least 15 times more massive than Earth. With an orbital period of 9.8 days, it does not transit its star, making its size difficult to measure. However, its gravitational influence was detected through the motion of the host star.
This outer companion could hold crucial clues about the formation of K2-360 b. Computer simulations suggest that gravitational interactions with K2-360 c may have driven the inner planet into its ultra-close orbit through a mechanism known as high-eccentricity migration.
Unique Formation and Evolution Insights
The high density of K2-360 b suggests an unusual evolutionary path. Unlike many close-in planets that migrate inward via gas-disk interactions, K2-360 b’s orbit might have been shaped by:
Gravitational Interactions: Likely caused by its outer companion, K2-360 c, which made its orbit highly elliptical before tidal forces stabilized it.
Tidal Circularization: A process where the planet’s orbit and rotation synchronized due to tidal interactions, possibly influenced by the planet’s spin-axial tilt.
Iron-Rich Composition Similar to Earth
Detailed models of K2-360 b’s interior reveal an iron-rich, rocky structure closer to Earth than Mercury:
Iron Core Proportion: 48% of the planet’s mass
Surface Features: Likely a molten magma layer due to intense stellar heat
“Our models suggest K2-360 b has a substantial iron core surrounded by a rocky mantle,” said Mahesh Herath, a co-author and Ph.D. candidate at McGill University.
Why K2-360 System Matters for Planetary Science
Ultra-short period planets like K2-360 b are rare, and their extreme properties offer a unique window into planetary evolution. The presence of a massive outer companion provides vital constraints on the formation theories of such systems.
“K2-360 is an exceptional laboratory for understanding planetary formation in extreme environments,” concludes Livingston.
The discovery of this multi-planet system provides valuable insights into how diverse planetary systems form and evolve across the galaxy, deepening our understanding of the processes shaping rocky worlds like our own.
Source: The Planet That Defies Physics: What’s Hiding Inside K2-360 b?
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