National Geographic recently posted an article about the discovery of a planet that seems to break the rules of planet formation.
CoRoT-20b is a gas giant about four-fifths the size of Jupiter, making it small for a gas giant, yet it has four times Jupiter’s mass, making it incredibly dense. So dense in fact, that astronomers can’t explain how this planet formed.
Traditionally, a gas giant has a solid, inner core, surrounded by an atmosphere composed of gas. Jupiter, for example, has a core that makes up 15% of the planet’s mass. CoRoT-20b, on the other hand, has a core that makes up 50-77% of the planet’s mass.
In order for CoRoT-20b to have formed, the planet would have had to suck up everything the star it orbits was spitting out (something that doesn’t happen under traditional planet formation models). Or the heavy metals could be distributed throughout the atmosphere of the gas giant instead of being collected in the solid core of the planet (something that astronomers haven’t seen before). Either way, CoRoT-20b is one strange planet. Obviously, more data is needed to solve these riddles.
I’m amazed at how many exoplanets we are discovering, how rapidly we are discovering them, and how strange they are. Not only are there WAY more planets than expected, but our very understanding of these planets is being challenged. It’s an amazing field that deserves far more attention.