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Solar System glossary

asteroids: small rocky or metallic bodies, most of which orbit the Sun between Mars and Jupiter
comets: made of ice and dust, these frozen pieces of leftover planets move in elliptical orbits around the Sun. As they approach it and begin to melt, comets may release glowing tails of dust and gas millions of miles long.
hydrostatic equilibrium: in a star, the balance acheived between the enormous outward pressure of gas heated by fusion and the inward pull of its own gravity.
mass: the amount of matter contained within a given object.
supernova: an explosion that occurs when a high mass star uses up its fuel and is unable to maintain hydrostatic equilibrium

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