Select all of the answers that apply. which of the following criteria do astronomers use to classify an object as a planet? the object orbits a star. the object is at least as large as mercury. its gravity makes the object spherical. the object clears its orbit of other objects. the object has an atmosphere.

The correct answers are: The object orbits a star. Its gravity makes the object spherical. The object clears its orbit of other objects.

According to the current definition of planet, as it is defined by the International Astronomical Union, a planet is a celestial body that fulfills with these three conditions: it orbits around a star, it is massive enough to have a spherical shape due to hydrostatic balance, and it has cleared its orbit of other objects. Around a star there are several kinds of orbiting objects, not all of them are spherical, like asteroids and comets, and while many of them are spherical (like many natural satellites), not all of them have cleared their orbit from the presence of other objects, like the case of Pluto. This definition was made after the debate about whether Pluto was to be considered a planet or not, and astronomers decided to create a new category in which Pluto fits: dwarf planets. These are massive spherical objects in direct orbit around their star that didn't clear up their orbit from the presence of other objects.

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