A planet is a spherical celestial body made up of a solid core and surrounded by an atmosphere.
It doesn't shine, which is what makes it different from a star, but it reflects the light from the star around which it orbits.
Because planets are much smaller, much less massive, and much less luminous (one billion times less than the star itself) than starts, they are very difficult to detect.
A planet is much smaller than a star. Their diameters are approximately :
A planet is much less massive than a star. Their masses are approximately :