Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Planetary Atmosphere Composition
Name: Salvador
Status: other
Grade: other
Location: FL
Country: N/A
Date: 1/20/2005


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


Replies:
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



Click here to return to the Astronomy Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory