Extrasolar Planet Composition
Date: Winter 2011-2912
How do astronomers determine the composition of extrasolar planets?
Good question. I think that other than identifying a single object
by its affect on its parent star, I do not think there is much they
can do regarding its composition. For example, an Earth-sized planet
would be described as being like Earth because of its small size; it
makes sense to suppose that it is rocky and watery. Moreover, a big
planet would probably be gaseous like Jupiter.
David H. Levy
Since the only data we get from extrasolar planets is what can be
"seen", that is the light coming from reflected off these planets,
then any knowledge we can conclude must be in the light. From how
often a particular planet blocks the light from its star, we can
calculate the planet's orbit. From the way the star wobbles, we can
calculate the gravitational effect a planet has on its star and
calculate the mass of the planet, from the absorption spectra of the
light reflected off the planet (adjusting for red shift), we can
determine the most prevalent atoms (particularly gases) that are
present and able to absorb particular wavelengths.
Greg (Roberto Gregorius)
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Update: June 2012