Activities: Using the attached table of values, make three graphs:

Sample plot:


Scientific context: Scientists use graphs like the ones you just made to try to determine how the solar system formed. The terrestrial planets are all small and rocky, and the outer planets (except for Pluto) are large and gaseous. Why? Scientists think that the planets all formed out of leftover material that was in a huge disk of gas and dust around the sun in the early days of the solar system. As material got farther from the sun (see exercise 3), the temperature got cooler, and some of the components began to condense and rain out. Heavy materials like iron and other metals were the first to condense out, and scientists think that this is why the terrestrial planets have high densities and are made up mostly of rock and metal. It wasn't until out near the orbit of Jupiter that the temperature got cool enough to allow volatiles like water and other ices to condense out of the disk, and this could be why the outer planets are made up mostly of gases and ices. This theory is still being developed, and scientists still aren't sure of all the details. It seems, however, that formation of planets is a natural by-product of star formation. We can see billions of stars in the sky, so it seems likely that at least some must have planets around them. Since planets are so much smaller (and therefore dimmer) than stars, they're hard to detect, but recently we've had the first confirmed discoveries of planets around other stars than the sun. As our telescopes and detectors get better and better, we seem sure to detect even more. So maybe someday we'll be able to see how our theories of planetary formation apply to other solar systems!

Back to Introduction or Forward to Activity 2

This module was written by Cynthia Phillips, Dept. of Planetary Sciences, University of Arizona, Tucson AZ, and funded in part by the NASA Spacegrant program.

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