This super-Earth defies planetary physics 🪐

In the immensity of space, a planet intrigues astronomers with its extreme properties. Nestled in the K2-360 system, the very special super-Earth K2-360 b could well redefine our understanding of rocky worlds.

Located 750 light-years from Earth, K2-360 b orbits its star in only 21 hours. It has a radius 1.6 times that of our planet, but its mass, nearly eight times greater, indicates an extraordinary density equivalent to that of lead. This unique feature makes it the densest planet in its category.


Such density is explained by a massive core likely composed of iron, representing nearly half of its total mass. This peculiarity suggests that K2-360 b is the remnant of a once larger world, stripped of its outer layers by the intense stellar radiation.

Astronomers assume the surface of this planet is covered in an ocean of magma—a direct consequence of its proximity to its star, subjecting it to extreme temperatures. This heat could also account for the disappearance of a potential primordial atmosphere.

In the same system, another planet, K2-360 c, is also intriguing. More massive, it completes an orbit around the star in 9.8 days. Its presence may have played a role in the current positioning of K2-360 b via a gravitational mechanism known as "high-eccentricity migration."

According to this process, K2-360 b's orbit was initially highly elliptical. Tidal forces exerted by the star would have later stabilized this trajectory into a close, circular orbit. These interactions highlight the complexity of planetary dynamics.

The discovery of K2-360 b, made possible by NASA's K2 mission and confirmed with ground-based telescopes, offers a unique opportunity to study planet formation in extreme environments. This particular system challenges existing models, especially regarding the evolution of super-Earths.

These ultra-dense worlds are rare, and their extraordinary characteristics provide insights into the diversity of planetary architectures in the universe. K2-360 b could serve as a model to explore the fate of other exoplanets that are close to their stars.

What is high-eccentricity migration?

High-eccentricity migration is a dynamic process that shapes the orbit of planets around their star. This phenomenon occurs when gravitational interactions between multiple celestial bodies disturb a planet's initial orbit. In such a scenario, a planet's orbit can become extremely elliptical, bringing it alternately very close to and very far from its star.

For K2-360 b, this migration would have been caused by interactions with its neighboring planet, K2-360 c. These forces could explain how such a massive planet ended up on an orbit so close to its star.

Astronomers use this mechanism to explain the presence of giant or rocky planets that are located very close to their star, defying traditional planetary formation models.