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Name: David
Status: educator
Grade: 6-8
Location: VA
Country: USA
Date: Winter 2011-2912


Question:
How do astronomers determine the composition of extrasolar planets?


Replies:
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.

Sincerely David H. Levy


David,

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) Canisius College



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