a dwarf planet usually is much smaller in size / in mass than other planets & pluto is a kind of dwarf planet ->  pluto is a dwarf planet that has much smaller mass than other planets  pluto is a dwarf planet that has much smaller mass than other planets & a dwarf planet is a kind of celestial object ->  pluto is a celestial object that  has much smaller mass than other planets  pluto is a celestial object that  has much smaller mass than other planets & as the mass of a celestial object decreases , the surface gravity of that celestial object weakens -> pluto will have much less gravity than other planets