Observatoire de Paris
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<-   Planets or stars?   ->
The two types of planets in our solar system : terrestrial planets and gaseous planets.
Crédit : NASA and Paris Observatory / UFE

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 :

  • Star : 1.400.000 km
  • Giant planet : 140.000 km
  • Earth : 13.000 km

A planet is much less massive than a star. Their masses are approximately :

  • Giant planet (ex : Jupiter) : 1000 times less massive than the Sun
  • Earth : 300 times less massive than Jupiter and 300,000 times less massive than the Sun.