Mega-Earth GJ 523b: a young, ultra-dense planet with a tilted orbit

GJ 523 b (BD+39 2675 b) is a recently confirmed planet orbiting a mid-type orange dwarf star called Gliese 523. This planet is unusually massive for its size, earning it the classification of a mega-Earth. At just 170 million years old, GJ 523b is much younger than most known exoplanets, and it orbits its star every 17.75 days. Its high density suggests it has very little gas, despite its large mass, which is rare for planets of this size.

Researchers used precise measurements of the star's motion to determine the planet's mass and orbit. They found that GJ 523b has a radius about 2.5 times that of Earth and a mass over 23 times greater. The planet's density is more than twice that of Earth, indicating a rocky composition with little or no atmosphere. The system's age was estimated using the rotation of the star and its companions. The planet's orbit is highly tilted compared to the star's rotation, a feature known as high orbital obliquity.

GJ 523b's combination of high mass, young age, dense composition, and tilted orbit challenges current ideas about how planets form and evolve. The study also introduces the term "mega-Earth" for ultra-dense, sub-Neptune-sized planets like GJ 523b.

Key findings
- GJ 523b is a massive, ultra-dense planet called a mega-Earth
- The planet is young, only 170 million years old
- It has a highly tilted orbit compared to its star's rotation
- Its high density suggests little or no gas envelope
- Mega-Earths are a new class of rocky exoplanets

Scientific study

GJ 523b is a Massive, 170 Myr-old Mega-Earth, Likely on a Polar Orbit (external link)