How do astronomers know that Jupiter is completely made of gases?

Question

I just am curious. Astronomers tell us that they are but how do they really know that.

Answer 1

We've sent probes and satellites there for one example.

Answer 2

various things come into play. and i do not believe that the planet is entirely completely gas.  There is a rocky, well, molten silicate, core that is more massive than the entire earth, from what I understand.

Anyway, you can get mass from gravitational behavior.  size can be estimated, so you get density.  surface composition is available from spectroscopy (light wavelengths indicate composition to simplify), chemical stability relations with P-T variations give an idea of what the planet has to have for proportional composition, to have the mass and density that is observed.  And that is basically it.  More to it than that, but those are the fundamentals.

Answer 3

Different gasses reflect white light in different spectrums of light. Scientists use  Spectrometers to figure out what gasses are in Jupiter. And that's how they know it's a gas planet

Answer 4

All the planets in the solar system were initiated by the rocky debris ejected by a super nova so they all contain some rocky material at their core.

  The sun was also started from the event of rocks crashing into a hydrogen field but it is likely no rocky material resides at the sun's core.

Answer 5

It's pretty simple really.

We know the chemical composition of Jupiter through analysis of it's spectrum.

"...The answer lies in the one of the many amazing things to do with light. (Come to think of it, light seems to be the answer most of the time in astronomy.) In this case, we use spectroscopy, which is studying the light from an object by the different wavelengths."

http://www.madsci.org/posts/archives/200...

This was known long before any probes were sent.

Each element has a unique spectral "signature" that is used to identify it.

http://en.wikipedia.org/wiki/Spectral_si...

Here's Jupiters :)

http://images.google.com/imgres?imgurl=h...

Answer 6

You can find the density of an object with the following

Density = mass / volume

We know the mass of Jupiter by the orbits of it's moons. The greater the mass, the greater the gravity, the faster the moons will orbit. So we know the value of the mass of Jupiter.

Furthermore, it's not too hard to measure it's size, there's various methods on how to do that. You could do some basic trig if you knew how much of the sky it occupied and it's distance.

So if you know these two, you can solve for density.

The density of Jupiter is low, really low... like a gas o_O

Still though, Jupiter isn't made completely of gas. As you get deeper within Jupiter, pressure builds, and that same pressure forces the hydrogen to assume a liquid like state called "liquid metallic hydrogen". Furthermore, beneath this there is believed to be a rocky core (based on planet formation models. Heavy objects sink to the centre of gravity, so any heavy objects should coalesce into a neat little sphere in the centre of Jupiter, the core).