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Name: Salvador
Status: other
Grade: other
Location: FL
Country: N/A
Date: 1/20/2005

I would like to know how is the composition (what kind of gases) of planets atmosphere is determined from the spaceship?

I believe the device used is called a spectrometer. When light travels through a gas, There are certain very specific wavelengths which are affected by the gas. Basically, every type of gas has a "thumbprint" which can be read by a spectrometer looking at light that had to pass through the planet's atmosphere.

Ryan Belscamper

Salvador- all I know is it is spectroscopy: Absorption vs. frequency, or emission vs. frequency.

There are probably a bunch of different kinds of spectroscopy:

- sunlight reflected off the surface, transmitted through the atmosphere,

- sunlight grazing the horizon, transmitted through the atmosphere,

- night-side glow from UV and ionization of the top of the atmosphere,

- far-infrared thermal emissions as the night-side tries to cool into space,

- characteristic absorption-peaks at certain radar frequencies as they go from satellite to ground and back,

- characteristic absorption-peaks of certain laser wavelengths when trying to bounce them off the ground,

- faint back scattering of an intense pulsed laser beam, in a gas or clear liquid or solid, happens with slight frequency shifts called "Raman scattering". The shifts are characteristic of the substances present.

This is a rather powerful technique. It does not require any surface-bouncing; it only needs clear enough gas for the laser-beam to reach the point you want to measure.

In addition, any space-ship in low orbit is sailing through the upper fringes of the atmosphere. The ship can take some into an instrument an and can test that any way it wants. You can usually tell the general type of atmosphere from that. But you might not pick up on some heavy minority components present at ground level.

Plenty of room here for the Klingons to do it differently than the Vulcans, in science-fiction stories. In real life, some NASA space probes can do it right now, too, if the atmosphere is clear enough. And astronomers are always collecting spectrographic data from earth telescopes and trying to fit that to atmospheric models.

Jim Swenson

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