[thedoc (OP)]

I've heard before that gas giants have no true surface. If you were visit one, would you sink in to the core, or would the mass on the surface" allow you to penetrate but only so far?
Asked by Allana
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[thedoc (OP)]

We answered this question on the show...

Heather Douglas put this to Dr Marc Rayman from NASA's Jet Propulsion Lab to see if he could clear the air...
Alanna - If I landed on a gassy planet, would I sink to the core?
Heather - Our Solar System has a whole host of different planet types. Some made of rock like, earth others of ice like Pluto and others made of gas like Jupiter. But what would happen if I were to travel past Mars, weave through the asteroid belt, and try to land on the gas giant? I spoke to Dr. Mark Raymen who works at NASA’s jet propulsion lab.
Marc - Although some planets seem to be gassy, they aren't like the light, airy, and substantial gas we generally think of. On Earth, the weight of the air above you pulled down by our planet’s gravity creates a modest pressure. This is about 1 kilogram per square centimetre. That’s the mass of a big book, like a dictionary if you remember those from the 20th century, pushing down on an area about the size of a single Lego brick. We conveniently call it 1 bar.
Heather - That's Earth, but what about Jupiter?
Marc - In contrast to our planet, gas planets are composed mostly of gas. They're also gigantic and the weight of all that gas is tremendous. For example, Jupiter is mostly hydrogen and it is enormous, 11 times the diameter of Earth and over 300 times the mass. It may have a rocky core that’s more than 10 times the mass of Earth. All that mass causes intense gravity, pulling downward on the gas which compresses it and creates fantastically high pressure.
Heather - More pressure than one dictionary, how many though? A hundred? A thousand? Ten thousand?
Marc - If you ever tried to land on a gassy planet, you would be subjected to pressure beyond anything you can imagine. As you descended below the colourful gas clouds, the pressure would grow and grow, rising to 1 million bar, at a depth of about 10,000 kilometres.
Heather - One million dictionaries.
Marc - You would be immersed in a sea of hydrogen so dense that it’s more like liquid than gas. At 20,000 kilometres, the pressure is around 2 million bars. That’s 2,000 times greater than the highest pressure found on Earth in the Mariana Trench in the deepest part of the Pacific Ocean.
Heather - Two million dictionaries.
Marc - The hydrogen is compressed so hard that the electrons are squeezed off. The strange condition makes the hydrogen metallic, but going still deeper, the pressure would continue to skyrocket, exceeding perhaps 40 million bars at the rocky core, more than 60,000 kilometres deep.
Heather - Forty million dictionaries.
Marc - If you ever tried to land on a gassy planet, you would not even make it to a few hundred kilometres. Your spacecraft,and you, would be utterly destroyed, squashed by the crushing atmospheric pressure, long before you found the core. So, you might sink to the core, but only in the form of squished atoms.
Heather - I don’t think I’ll be going to Jupiter after all. Thanks for clearing the air on this one, Marc. Next week, we’re sequencing Lorianna’s question…
Lorianna - I was wondering why the mother doesn’t reject a baby because it has a different genetic sequence.

[chiralSPO]

My understanding is that there is a solid core at the center of Jupiter (not sure about planets like Saturn). Even in Jupiter's case, the solid part is an incredibly small fraction of the planet. One could say that it is a rocky planet with an enormous atmosphere, but since there is so much "atmosphere" it really doesn't make sense to talk about it that way.

[alancalverd]

If there is no phase change ("surface") you can't land on it!

[Pecos_Bill]

It would not be difficult to land on Jupiter or any other planet.

If you should want to be able to take off again, that is an entirely different kettle of fish and a horse of a different color.

[SiempreFillInTheBlank]

I think the ship would get stuck somewhere in the upper atmosphere when the density of the ship equals the density of the surrounding gas. It would be like a hot air balloon kind of floating a few hundred meters above the ground (except theres no ground to see). Or like how some fauna spend most their life in a band of the ocean. Also you would get blown around at hurricane speeds in the gas bands. So while you can't land, you could float around on a cruise.

[chiralSPO]

I agree that the ship would sink to the depth at which its density was about the same as the surrounding environment and go no further. However, if that ship is made of anything denser than hydrogen, it will have a very long fall.

Yes, the pressure increases and the hydrogen becomes a metallic liquid, but that really isn't very dense (Jupiter has an overall average density of about 1.3 g/cm³). And we should not forget that those incredibly high pressures will also act on the ship! The solid parts of the ship may not be very compressible, but the whole thing would probably crush like a tin can if you had any atmosphere (and would certainly sink to the core if there were no atmosphere on board!)