Scientists currently believe that the axis of Earth is tilted because, early in its formation, it was hit by a nearly planet-sized object. The collision not only knocked Earth off its perpendicular axis but also created the debris that became the Moon. Scientists call this explanation the ...
Solar system, assemblage consisting of the Sun and those bodies orbiting it: 8 planets with about 210 known planetary satellites; many asteroids, some with their own satellites; comets and other icy bodies; and vast reaches of highly tenuous gas and dust