As everybody knows Jupiter is made up of gases and these gases mainly contain hydrogen and helium. Since light passes through gases and does not reflect when shining on them, how we are able to see Jupiter? What is the physics behind it?

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    $\begingroup$ Light doesn't reflect gases? Then explain this bottle of chlorine gas? $\endgroup$ – Kyle Kanos Jul 21 '15 at 15:38
  • $\begingroup$ if gases reflects lights and light does not pass through then can we able to see each other? and cl is itslef having colour @KyleKanos $\endgroup$ – SpringLearner Jul 21 '15 at 15:47
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    $\begingroup$ Light does indeed reflect off molecules in gases, it is just that not all of the light is reflected in the visible band. $\endgroup$ – Kyle Kanos Jul 21 '15 at 16:10
  • $\begingroup$ possible duplicate of Why can't we see gases? $\endgroup$ – Carl Witthoft Jul 21 '15 at 16:19
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    $\begingroup$ As the answers show, this is not really a duplicate. $\endgroup$ – Emilio Pisanty Jul 21 '15 at 17:01

In general, what you see in Jupiter's atmosphere is simply clouds: large collections of small liquid droplets floating in the atmosphere. Liquid droplets are excellent at scattering light in any direction, and indeed one can visually see clouds on Earth with some regularity.

In fact, it is indeed possible to observe 3D details on these clouds. Here is an example from Saturn:

enter image description here

Image source

It is clear that most of the reflected light comes from clouds, which are bathed in a (mostly) transparent atmosphere.

The Wikipedia article on Jupiter's atmosphere makes it clear that it is indeed the clouds that are visible. These inhabit the troposphere, and there are another three layers of atmosphere (stratosphere, thermosphere and exosphere) sitting on top of it which are mostly transparent (much like Earth!).

However, you should also note that:

  • Gases are transparent but only up to a point, and they do scatter light in all directions (including backwards). In fact, the air on Earth's surface does scatter light, which is why the sky isn't black. What matters is the thickness of gas that the light must travel through - a few meters in air is fine, but, on the other hand,
  • Jupiter is big. Like, really big. If it was in fact simply made of hydrogen and helium at constant atmospheric pressure and density, you still wouldn't be able to see through it.
  • Jupiter is made (mostly) out of hydrogen and helium, but that doesn't mean that the hydrogen and helium are gaseous. As you descend into Jupiter, the gaseous atmosphere smoothly transitions into liquid, and then you meet a mantle made of metallic hydrogen. The centre is a core of ice and rock.

    enter image description here

    Image source

For a better look at Jupiter, I heartily recommend Phil Plait's Crash Course Astronomy:

enter image description here.

  • $\begingroup$ very nicely explained +1,can you please explain the second point If it was in fact simply made of hydrogen and helium at constant atmospheric pressure and density, you still wouldn't be able to see through it. $\endgroup$ – SpringLearner Jul 21 '15 at 17:21
  • $\begingroup$ As I explained, all gases scatter light to some extent. Jupiter is so thick that any sort of scattering will make it opaque. You're used to seeing the stars through ~100km of atmosphere, but Jupiter is 70,000km thick. $\endgroup$ – Emilio Pisanty Jul 21 '15 at 17:30
  • $\begingroup$ "Space is big. Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space." $\endgroup$ – Robin Ekman Jul 22 '15 at 12:44

Jupiter is cloudy. It's upper atmosphere contains clouds of ammonia, ammonium hydrosulfide and water. These clouds reflect light just as clouds made up of water droplets reflect light in Earth's atmosphere.

We should note that no gas is completely transparent, even if only because of Rayleigh scattering. The sky on Earth looks blue because our atmosphere scatters light - the colour is because it scatters blue light more than red light. However the majority of the light we see coming from Jupiter has been refleted from the tops of clouds.

  • $\begingroup$ That's a first, I think. I usually find my one-paragraphers buried under awesome answers of yours. In fact, I think I'll go look for some of those to upvote. $\endgroup$ – Emilio Pisanty Jul 21 '15 at 16:21
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    $\begingroup$ I was just thinking dammit Emilio has top trumped me :-) $\endgroup$ – John Rennie Jul 21 '15 at 16:23
  • $\begingroup$ * It's upper atmosphere contains clouds of ammonia, ammonium hydrosulfide and water* hydrogen being lighter why it does not stay at upper atmosphere? $\endgroup$ – SpringLearner Jul 21 '15 at 17:22
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    $\begingroup$ @SpringLearner: on Earth clouds are made from water droplets and/or ice crystals that are denser than air, yet they stay up. The reason they stay up is because the droplets/ice crystals are very small and their terminal velocity in air is smaller than the air currents in the atmosphere. Exactly the same argument applies to clouds on Jupiter. $\endgroup$ – John Rennie Jul 21 '15 at 17:27

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