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One idea is to simply define a planet as a natural object in space that is massive enough for gravity to make it approximately spherical. But some scientists object that this simple definition does not take into account what degree of measurable roundness is needed for an object to be considered round.
In 2006, the International Astronomical Union (IAU) adopted a definition of a planet in the Solar System, placing the four terrestrial planets and the four giant planets in the planet category; Ceres, Pluto, and Eris are in the category of dwarf planet.
17 Φεβ 2022 · Space is the zone above and around our planet where there is no air to breathe or to scatter light. Space is a vacuum, but it is far from empty.
27 Ιουν 2019 · What Is a Planet? The Short Answer: A planet must do three things: it must orbit a star, it must be big enough to have enough gravity to force a spherical shape, and it must be big enough that its gravity cleared away any objects of a similar size near its orbit. This cosmic cloud, called Sharpless 2-106, is an area where stars (and planets) form.
One idea is to simply define a planet as a natural object in space that is massive enough for gravity to make it approximately spherical. But some scientists objected that this simple definition does not take into account what degree of measurable roundness is needed for an object to be considered round.
What is a planet? A planet is a celestial body that is in orbit around a star; it has enough mass for its gravity to create a round shape; and it has cleared its neighborhood of smaller objects.
After much debate, it was decided that a planet should be defined as an object which (a) orbits the sun, and (b) is massive enough not only to coalesce itself into a nearly spherical shape, but also to gravitationally dominate its region of the solar system.
