{image}
How many planets are there?
So what definition have they decided on?
For a celestial object to be considered a planet, it must satisfy two conditions:
1- The object must be in orbit around a star, but must not itself be a star
2- It must have enough mass for the body's own gravity to pull it into a nearly spherical shape
Any object with a mass greater than 0.6% that of our Moon and a diameter greater than 800km would normally meet the second condition. But borderline cases will have to be resolved by more observation.
Some objects currently considered to be moons and asteroids could be eligible if they meet those basic tests. So the definition leaves the door open for other objects to join the expanding club.
@ BBC: Q&A New planets proposal
