Super Earth discovered with record density

A lead-heavy exoplanet, possibly the leftover core of a giant planet that flew too close to its sun, has just been discovered .

Named K2-360 b , the exoplanet is 7.7 times more massive than Earth but only 1.6 times the size. It has a density of about 11 g/cm³, which is about the same as lead and twice the density of Earth.

Among the ultra-short-period super-Earths, K2-360 b is the densest.

Close-up illustration of K2-360 b (red) orbiting its star (Image: Astrobiology Center).

A planet's period is the period we call a year, or the time it takes for a planet to complete one orbit around its star. K2-360 b is nicknamed "ultrashort" because its year is just 21 hours long on Earth.

Thanks to its close proximity to its star, the exoplanet was easily detected by astronomers, who have figured out some of the reasons why it is so dense.

In 2016, when NASA's K2 project discovered the shadow of this planet on its star , scientists immediately investigated and discovered that this was an unknown exoplanet.

Digging deeper, they measured the mass and radius and calculated the density of K2-360 b. In contrast, exoplanets have a density of only 0.03 g/cm³, or you can imagine them as light as cotton candy.

To figure out what makes K2-360 b so solid, the team created a model that simulates the core of this super-Earth, based on observations of it and its host star.

Models suggest that the planet has a large iron core that makes up about 48% of its mass . K2-360 b may be the dead core of a world that was once much larger and farther away from its host star.

Over time, it drifts closer, where intense radiation washes away atmospheric gases and leaves behind a solid mass of rock that is likely to be completely covered with lava.

Another discovery supported the team's claim. They discovered that further away from K2-360 b is a much larger planet, dubbed K2-360 c , that is similar in size and density to Neptune.

Dynamical models suggest that due to the eccentric migration, K2-360 c may have pushed the smaller planet K2-360 b into its current orbit very close to the star.

The gravitational interaction between these bodies causes K2-360 b's orbit to become elliptical, which tidal forces then cause it to rotate and move closer to the star.

The findings of this study add to the growing body of evidence that the universe is filled with strange planets that seem to exist only in works of science fiction.