QUESTION:
Could a camera be made that is an x-ray type camera that could see
through the atmosphere of Neptune to its rocky core--to see if it is made
out of nitrogen, methane, and carbon monoxide, like Pluto?

ANSWER from Chris Burrows on March 28, 1996:
X-ray telescopes can be built, and have been used to study many astronomical
objects.  The problem is that we can only study objects that emit x-rays.  When
you take an x-ray photograph of somebody's broken leg, you need a source of
x-rays to project through the leg, and a detector (film) on the other side.  We
can build the detector, but no source of x-rays is even nearly
strong enough to penetrate through Neptune's atmosphere.  In fact, x-rays don't
even get through our own atmosphere - which is why we need to send satellites
above our atmosphere to study sources that emit x-rays.  So how can you see
inside a planet?

One way is to send a probe into the atmosphere - like was just done by the
Galileo probe at Jupiter. Unfortunately, probes that we know how to build get 
destroyed by the high pressure after only penetrating to a small depth.  (maybe
 a few hundred kilometers).  Other methods are more indirect.  You can study 
seismic waves, and model their propagation time and paths through the planet
-We have done a lot of such studies for the sun, earth and moon.  Or you can
look carefully at the effects of the planet's gravity on a satellite's orbit.
Small changes in the orbit can be used to understand how the planet is made up.
Because the gas giants have very convective atmospheres, they dredge
up material from large depths to their surface.  So you can study their
composition by looking at that material.

Finally, you can weigh the planet by seeing how it perturbs
other planets, and you can measure its size by looking with a telescope. Did
you read this week's New York Science Times?  In the laboratory you can
determine how hydrogen and other materials behave at high pressures and
temperatures.  Then you can ask how the planet must be made up to have the
right size and density.

Hope this helps!

Chris