Determining the Composition Layers of Planets
How do astronomers determine the composition and layers
of the planets, especially the outer four planets?
Since the outer planets are gaseous giants, they can determine the
structure through spectroscopic observations. For example, Jupiter's
outer layers come out best in methane light.
Hope this helps!
David H. Levy
In order for us to determine anything we have to have data. This
means that something from the outer four planets must reach us.
Before the days when we could send probes to the other planets,
there was one thing that certainly reached us from these planets:
light (we could certainly "see" the planets so light that has
bounced off from these planets have reached us).
Light has a distinctive way of reacting with matter. Just think of
how certain substances are differently colored from others. This
means that all forms of matter have a distinct "fingerprint" of
light reflection or emission. So, imagine we focus our telescopes
onto a planet, collect the light that bounced off that planet, then
we can analyze the light and look for distinctive patterns of
particular elements or substances. ...this is not easy, because all
the elements and substances will be reflecting back light at the
same time and the data is a mash-up of all these patterns. However,
with good detective work and analysis, we have been able to
determine the composition the gas planets and the atmospheres above
the inner planets.
Greg (Roberto Gregorius)
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Update: June 2012