How do astronomers distringuish different types of exoplanets?

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Offline chris

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When astronomers pick up an exoplanet orbiting a distant star, how do they know what it's made of?
I never forget a face, but in your case I'll make an exception - Groucho Marx


Offline evan_au

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With current technology, we can only very rarely see the planet directly.

So astronomers aren't sure of the composition, but they can make some educated guesses.

What they do know is:
  • The type of star, from which they can estimate the star's size and mass
  • The period of the planet's orbit, which tells them its distance from the star
  • How much the planet is swinging the star around in its orbit, which gives the mass of the planet
  • How physically big the planet is, compared to the star (if the planet passes in front of the star)
Given estimates of the size and mass of the planet, astronomers can calculate the planet's density:
  • If it has a density around 5 times higher than water, it is probably an iron-cored planet like Earth
  • If it is large, and has a density of less than 1.5 times that of water, it is probably a gas giant like Jupiter or Saturn
  • Intermediate values may represent a mixture of rock and water or ices
  • From the mass of the planet, and its temperature, they can estimate the likelihood that the planet could hold on to an atmosphere

In future, several orbiting satellites could be combined to form a large telescope which could block out the light from a distant star, and obtain images of exoplanets directly. By taking a spectrum of the light from each planet, the composition of the atmosphere can be determined, and possibly the composition of a surface below the atmosphere.


Offline RD

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As the exoplanet eclipses its star the starís light will pass through the exoplanetís atmpsphere and introduce new dark bands into the absorption spectrum that tell which elements are present in the exoplanet atmosphere.

see ...
« Last Edit: 20/07/2012 12:42:53 by RD »