Everything we have ever seen in nature is built out of 92 unique atomic building blocks called the chemical elements. An element is identified and named depending on the size of its atomic core, called the nucleus. Hydrogen is the simplest and lightest element, whereas uranium is the heaviest element found to occur naturally in nature. Using an instrument called a spectrometer that breaks white light up into the colors of the rainbow, astronomers can determine which elements make up the rocky debris that originates in asteroids that have fallen onto the white dwarf. Thus, it is possible to figure out the chemical composition of the rocky objects that orbit around white dwarf stars. Planetary scientists believe that the rocky planets Mercury, Venus, Earth, and Mars in our own solar system were built up, 4.6 billion years ago, from accumulation of huge numbers of smaller objects similar to the asteroids that now orbit the Sun between Mars and Jupiter. We now have direct samples of these asteroids in the form of meteorites that fall to Earth; meteorites are little pieces broken off from asteroids that suffered collisions long ago.

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