 The 2006 debate surrounding Pluto and what constitutes a planet led to Ceres being considered for reclassification as a planet . A proposal before the International Astronomical Union for the definition of a planet would have defined a planet as " a celestial body that ( a ) has sufficient mass for its self @-@ gravity to overcome rigid @-@ body forces so that it assumes a hydrostatic equilibrium ( nearly round ) shape , and ( b ) is in orbit around a star , and is neither a star nor a satellite of a planet " . Had this resolution been adopted , it would have made Ceres the fifth planet in order from the Sun . This never happened , however , and on 24 August 2006 a modified definition was adopted , carrying the additional requirement that a planet must have " cleared the neighborhood around its orbit " . By this definition , Ceres is not a planet because it does not dominate its orbit , sharing it as it does with the thousands of other asteroids in the asteroid belt and constituting only about a third of the mass of the belt . Bodies that met the first proposed definition but not the second , such as Ceres , were instead classified as dwarf planets . 
 The 2006 debate surrounding Pluto and what <a href='uninflect' title='1'><mark>constitutes</mark></a> a planet led to Ceres being considered for reclassification as a planet . A proposal before the International Astronomical Union for the definition of a planet would <a href='been_done' title='2'><mark>have</mark></a> defined a planet as " a celestial body <a href='null_relcl' title='3'><mark>that</mark></a>( a ) <a href='got' title='4'><mark>has</mark></a> sufficient mass for its self @-@ gravity to overcome rigid @-@ body forces so that it <a href='uninflect' title='5'><mark>assumes</mark></a> a hydrostatic equilibrium ( nearly round ) shape , and ( b ) is in orbit around a star , and <a href='drop_aux' title='6'><mark>is</mark></a>neither a star nor a satellite of a planet " . Had this resolution been adopted , it would <a href='been_done' title='7'><mark>have</mark></a> made Ceres the fifth planet in order from the Sun . This never happened , however , and on 24 August 2006 a modified definition was adopted , carrying the additional requirement that a planet must <a href='been_done' title='8'><mark>have</mark></a> " cleared the neighborhood around its orbit " . By <a href='None' title='9'><mark>this</mark></a><a href='negative_concord' title='10'><mark>definition</mark></a> , Ceres <a href='negative_concord' title='11'><mark>is</mark></a> <a href='negative_concord' title='12'><mark>not</mark></a><a href='None' title='13'><mark>a</mark></a><a href='negative_concord' title='14'><mark>planet</mark></a> because it <a href='uninflect' title='15'><mark>does</mark></a> not dominate its orbit , sharing it as it <a href='uninflect' title='16'><mark>does</mark></a> with the thousands of other asteroids in the asteroid belt and constituting only about a third of the mass of the belt . Bodies <a href='null_relcl' title='17'><mark>that</mark></a>met the first proposed definition but not the second , such as Ceres , <a href='uninflect' title='18'><mark>were</mark></a> instead classified as dwarf planets . 
The 2006 debate surrounding Pluto and what constitute a planet led to Ceres bein considered for reclassification as a planet . A proposal before da International Astronomical Union fir the definition of a planet would done defined a planet as " a celestial body ( a ) got sufficient mass for its self @-@ gravity to overcome rigid @-@ body forces so that it assume a hydrostatic equilibrium ( nearly round ) shape , and ( b ) is in orbit around a star , and neither a star nor a satellite of a planet " . Had dis resolution been adopted , it would done made Ceres the fifth planet in order from tdaSun . This never happened , however , and on 24 August 2006 a modified definition was adopted , carrying the additional requirement that a planet must done " cleared thdaeighborhood around its orbit " . By no definition , Ceres ain't no planet because it do not dominate its orbit , sharing it as it do wit thedaousands of other asteroids in the asteroid belt and constituting only about a third of the mass of the belt . Bodies met the dast proposed definition but not the second , such as Ceres , was instead classified as dwarf planets .