MADRID, November 15, 2024 - A newly discovered multiplanetary system around a Sun-like star includes an ultra-short period planet with one of the highest densities ever measured. The findings, published in Scientific Reports, shed light on the formation and evolution of planets in extreme environments.
The system, named K2-360, is located approximately 750 light-years from Earth and consists of two planets orbiting a star similar to our Sun. The first, K2-360 b, is a super-Earth with a short orbital period, roughly 1.6 times the size of Earth, and completes its orbit every 21 hours. With a mass 7.7 times greater than Earth, it is the most characterized and dense planet of its type discovered to date.
The second planet, K2-360 c, is a larger outer planet at least 15 times more massive than Earth, orbiting its star every 9.8 days. Its exact size remains unknown as it does not transit in front of its star.
John Livingston, the lead author from the Tokyo Astrobiology Center, noted, "K2-360 b is remarkable: it is as dense as lead, concentrating nearly eight Earth masses in a sphere slightly larger than our planet." This extreme density suggests it may be the stripped core of a once larger planet that lost its outer layers due to intense radiation from its nearby star.
The discovery was facilitated by NASA's K2 mission, which first detected the inner planet transiting in front of its star in 2016. Follow-up observations with ground-based telescopes confirmed the planet's nature and revealed the presence of the outer companion.
Researchers believe that K2-360 b's formation involved unique dynamics. Computer simulations indicate that the outer planet may have played a crucial role in pushing the inner planet into its current tight orbit through a process known as high eccentricity migration.
The analysis suggests K2-360 b has a composition rich in iron, more similar to Earth than Mercury, with an estimated iron core constituting about 48% of its mass. This positions it closer to being a super-Earth rather than a super-Mercury, despite its extreme density.
Understanding planets like K2-360 b aids in reconstructing how terrestrial planets form and evolve under varying conditions throughout the galaxy. The discovery of the K2-360 system provides valuable insights into planetary system architectures and the processes shaping them.