Question

when pluto was first discovered in 1930, it was accepted as the ninth planet in our solar system. however, it lost that status in 2006 when the international astronomical union created a new classification of celestial bodies: dwarf planets, the category into which pluto was moved, are similar to regular planets in two ways: both types of planets orbit the sun and contain sufficient mass to have been shaped into spheres by gravity. the primary difference between regular planets and dwarf planets involves their orbits. regular planets have cleared their “neighborhoods” of other objects by deflecting or consuming the smaller bodies that they have encountered, leaving their orbits relatively unobstructed. a dwarf planet like pluto, however, has not cleared its orbit. pluto is one of many small, icy objects in its region of space, and since it does not have significantly more mass than these objects, it has not managed to absorb them, nor to move them away through direct contact or gravitational interactions. pluto was considered a planet from 1930 to 2006, at which point it was reclassified. dwarf planets like pluto are distinguished from actual planets by the characteristics of their orbits. regular planets and dwarf planets both have enough mass to become spherical, and they both orbit the sun. what is the main, or central, idea of the passage?

Explanation:

The passage discusses Pluto's classification as a planet until 2006 and its re - classification as a dwarf planet. It explains the key difference between regular planets and dwarf planets in terms of their ability to clear their orbits of smaller bodies through gravitational interactions. Regular planets have cleared their neighborhoods, while dwarf planets like Pluto have not.

Answer:

The main idea is that regular planets have cleared their orbital neighborhoods of smaller bodies through gravitational interactions, while dwarf planets like Pluto have not been able to do so, which led to Pluto's reclassification from a planet to a dwarf planet in 2006.