To date, researchers have found 188 planets orbiting other stars. Of these 188, 10 are known to be "transiting planets" which means that the planet passes in between their star and Earth (line of sight) in their orbits. Only gas giant sized planets in close orbits to their stars have been identified as transiting planets due to limitations in detection techniques and equipment. The point is that these transiting planets can have both mass and density determined, which in turn can tell us about the composition of the planets. The researchers found that the heavy element make up of the planet was related to relative heavy metal makeup of it's star. Core sizes on these planets can range from 1 earth mass to 100 earth masses.
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Extrasolar Planets
