Astronomers have identified K2-360 b, a newly discovered Super-Earth with a density comparable to lead. This rocky planet, with a mass equivalent to 7.7 Earths, measures only 1.6 times the size of Earth, resulting in a remarkable density of approximately 11 grams per cubic centimeter.
K2-360 b belongs to the ultra-short-period (USP) Super-Earth category, completing an orbit around its star in just 21 hours, making it the densest known planet in its class. Discovered in 2016 by NASA's K2 mission, follow-up observations have allowed for precise measurements of its mass and radius.
The planet's lead-like density is twice that of Earth and surpasses other high-density exoplanets like GJ 367b and TOI-1853b. However, TOI-4603b, with a density of 14.1 grams per cubic centimeter, challenges K2-360 b's record, although it may be classified as a brown dwarf rather than a traditional exoplanet.
To understand K2-360 b's solid composition, researchers developed a model of its interior, suggesting a substantial iron core constituting about 48 percent of its mass. The formation of such a dense planet is theorized to result from the remnants of a larger gas giant that migrated closer to its star, leading to atmospheric loss and leaving behind a rocky core.
Additional insights were gleaned from the star's wobble, indicating the presence of a larger companion planet, K2-360 c, likely similar to Neptune. Astrophysicist Alessandro Trani from the Niels Bohr Institute noted that gravitational interactions could have caused K2-360 b's tight orbit through a process called high-eccentricity migration.
This discovery underscores the diversity of planetary systems in the universe, revealing worlds that challenge our understanding of planetary formation.