Wait but there’s a better comment. I thought I had it below, but this one was the one I was actually searching for:https://www.reddit.com/r/askscience/comments/12eggw/seeing_as_how_jupiter_is_a_gas_giant_

Well, if you weren’t wearing a space suit, no matter where you started you would die almost instantly because there is essentially no oxygen at any level of Jupiter’s atmosphere.

But let’s say you do have a space suit. What do you mean by “step foot on it”? Jupiter is, as you noted in your question, a gas giant, meaning it’s made of gas. There is no solid surface. And just like Earth’s atmosphere, the gas doesn’t really have a “top”, it just gets thinner and thinner as you get further and further from the planet, until at some point it is indistinguishable from interplanetary space (which, you may be interested to know, is not a true vacuum

.

But let’s say you just get dropped from some height way outside of Jupiter’s visible atmosphere. Once you got within about 200,000 miles (about 300,000 km) of the planet’s surface, you’d die fairly quickly from radiation poisoning.

But let’s say your space suit has radiation-resisting superpowers. Well due to Jupiter’s extreme mass, you’d quickly accelerate through the tenuous upper atmosphere at about 2.6 g, and burn up just like a meteor flying through Earth’s upper atmosphere.

But let’s say we dropped you in the middle of Jupiter’s upper atmosphere, where the pressure were just about the same as Earth’s surface pressure (1 bar). Now we’re getting somewhere. You’d be falling, but since you’re already in the thicker part of the atmosphere, your terminal velocity will be fairly low (taking Jupiter’s higher gravity and the atmosphere’s lower density into account (it is mostly hydrogen, so its density is about 10 times less than Earth’s even though the pressure is similar), your terminal velocity would be about 3200 km/h (2000 mph)). This is probably slow enough that frictional heating and heating from supersonic compression would not burn you up.

But hell, for shits and giggles, and in the name of keeping you alive as long as possible, let’s give you a parachute, a little smaller than the one given to the Galileo probe, so that you fall at about the same velocity initially (~100 m/s, or about 360 km/h, 220 mph). Now we’re cooking. Not literally though, because the temperature at this level is fairly comfortable: The temperature is just about 0 C (32 F), so you’d actually be pretty comfy.

So okay, now you’re in your radiation-proof spacesuit, with your handy parachute, falling through the atmosphere just at the top of the clouds. These clouds are made

Well, if you weren’t wearing a space suit, no matter where you started you would die almost instantly because there is essentially no oxygen at any level of Jupiter’s atmosphere.

But let’s say you do have a space suit. What do you mean by “step foot on it”? Jupiter is, as you noted in your question, a gas giant, meaning it’s made of gas. There is no solid surface. And just like Earth’s atmosphere, the gas doesn’t really have a “top”, it just gets thinner and thinner as you get further and further from the planet, until at some point it is indistinguishable from interplanetary space (which, you may be interested to know, is not a true vacuum

.

But let’s say you just get dropped from some height way outside of Jupiter’s visible atmosphere. Once you got within about 200,000 miles (about 300,000 km) of the planet’s surface, you’d die fairly quickly from radiation poisoning.

But let’s say your space suit has radiation-resisting superpowers. Well due to Jupiter’s extreme mass, you’d quickly accelerate through the tenuous upper atmosphere at about 2.6 g, and burn up just like a meteor flying through Earth’s upper atmosphere.

But let’s say we dropped you in the middle of Jupiter’s upper atmosphere, where the pressure were just about the same as Earth’s surface pressure (1 bar). Now we’re getting somewhere. You’d be falling, but since you’re already in the thicker part of the atmosphere, your terminal velocity will be fairly low (taking Jupiter’s higher gravity and the atmosphere’s lower density into account (it is mostly hydrogen, so its density is about 10 times less than Earth’s even though the pressure is similar), your terminal velocity would be about 3200 km/h (2000 mph)). This is probably slow enough that frictional heating and heating from supersonic compression would not burn you up.

But hell, for shits and giggles, and in the name of keeping you alive as long as possible, let’s give you a parachute, a little smaller than the one given to the Galileo probe, so that you fall at about the same velocity initially (~100 m/s, or about 360 km/h, 220 mph). Now we’re cooking. Not literally though, because the temperature at this level is fairly comfortable: The temperature is just about 0 C (32 F), so you’d actually be pretty comfy.

So okay, now you’re in your radiation-proof spacesuit, with your handy parachute, falling through the atmosphere just at the top of the clouds. These clouds are made of ammonia, but let’s just assume your spacesuit and parachute are okay with that. You’d actually be okay for quite a while; maybe a little bored, but hey, you’re on motherfucking Jupiter.

After about 5 minutes, you’ve fallen to the 2-bar level (about twice the average surface pressure on Earth). You are now falling through different clouds, made of ammonium hydrosulfide and ammonium sulfide

. They don’t look much different than regular clouds, but they do have a brownish tint that gets browner the deeper you go. Some people may find this surprising, but you won’t feel many ill effects, even as the pressure increases rapidly. The bends are only seen with rapid decompression; the only ill effects from rapid compression are if the compression is too rapid to allow your body cavities (such as inner ear, sinuses, etc) to equalize. So as long as your ears are clear of wax, you should be fine.

About 10 minutes later, you have reached the 4 bar pressure level, which is about 4 times the average atmospheric pressure at sea level, or about the pressure you’d experience under 30 meters (100 feet) of water. The temperature has actually gotten quite cold, and is now around -40 C (-40 F). But assuming all the capabilities your spacesuit already had, I’m sure it wouldn’t be too much to ask for a small heater. You are now passing through clouds of water ice, just like you might see at high altitudes on Earth, but it is getting very dark. You are also being whisked along horizontally by winds reaching 200 m/s (450 mph, 720 km/h), but you barely notice as they are not very turbulent.

15 more minutes go by, and you are now at a pressure of 10 bar, or 10 times normal sea-level atmospheric pressure. At bit before this level you should have changed the mixture of air you are breathing; if you breathed normal air at a pressure of 10 bar or more, you would suffer from acute oxygen toxicity , which can be quickly fatal (oxygen is actually toxic at much lower pressures, but it would take much longer than our quick decent through jupiter). At the same time, you can suffer from nitrogen narcosis

, which has similar symptoms to inhaling nitrous oxide initially, but can quickly progress to severe symptoms like coma or death. So as you dive deeper your magic space suit also changes the mixture of air you are breathing, so that the partial pressures of oxygen and nitrogen remain the same as you are used to breathing, with the rest filled with helium or neon, which are the only known gasses which don’t exhibit a toxic effect at high pressures. But provided this is all taken care of, you are actually quite comfortable, as the temperature has risen back up to about 23 C (73 F).

Another 25 minutes pass, and you are starting to realize you’re in trouble. You are in complete darkness now, and the temperature has been steadily increasing as you go further down: now over 100 C (212 F) and still rising fast. Your spacesuit’s systems are starting to fail. Within a few minutes, the temperature is over 200 C (392 F), and you don’t have much longer to survive. Not wanting to endure a miserable, burning death, you take your conveniently placed cyanide capsule and end your interplanetary adventure.

But your body keeps falling.

Down into interior regions where we have little ideas of the exact composition. Pressure and density are increasing drastically, slowing your descent to a crawl. The atmosphere of mostly hydrogen is actually a liquid now, and is now several thousand degrees, but with essentially no oxygen around your body turns into a charcoal-like substance. Your parachute cuts away, but your spacesuit remains intact because it is convenient to the story, and your compressed, dead chunk of bodily substance slowly sinks, beyond 1,000 bar, beyond 10,000 bar…

Until finally, at an insanely crushing pressure of 2,000,000 bar (and a temperature of 5,000 K, about the temperature of the surface of the sun!), you stop sinking. Because your super-spacesuit is conveniently still intact, your body is still mostly water, which is essentially incompressible, even at these incredible pressures. As such, at this level, where the density is about 1 g/cm3 or about 1000 kg/m3 (this is approximately the density of water) you and the surrounding atmosphere are the same density, so you will no longer sink! So there your carbonated corpse floats, for all eternity, until the heat death of the universe.

Sources (among some others linked above in-line):

http://www.agu.org/journals/je/v103/iE10/98JE01766/98JE01766.pdf
http://lasp.colorado.edu/education/outerplanets/giantplanets_interiors.php
http://www.hq.nasa.gov/pao/History/conghand/fig15d3.gif

http://thesciencepundit.blogspot.com/2010/04/air-friction-myths.html http://en.wikipedia.org/wiki/Terminal_velocity#Examples http://en.wikipedia.org/wiki/Atmosphere_of_Jupiter#Vertical_structure

Hope you enjoyed reading!

One of my all time favorite Reddit comments it’s about this. Astrophysics PhD /u/astromike23 answers in this comment

The following is the pasted text:

For the interior of Jupiter, let’s imagine taking a descent from cloud-tops down to the core based on our best guesses of what lies below.

You start falling through the high, white ammonia clouds starting at 0.5 atmospheres, where the Sun is still visible. It’s very cold here, -150 C (-240 F). Your rate of descent is roughly 2.5x that of Earth, since gravity is much stronger on Jupiter.

You emerge out the bottom of the cloud deck somewhere near 1 atmosphere. It’s still somewhat bright, with sunlight filtering through the ammonia clouds much like an overcast day on Earth. Below, you see the second cloud-deck made of roiling brown ammonium hydrosulphide, starting about 2 atmospheres.

As you fall through the bottom of this second cloud deck, it’s now quite dark, but warming up as the pressure increases. Beneath you are white water clouds forming towering thunderstorms, with the darkness punctuated by bright flashes of lightning starting somewhere around 5 atmospheres. As you pass through this third and final cloud-deck it’s now finally warmed up to room temperature, if only the pressure weren’t starting to crush you.

Emerging out the bottom, the pressure is now intense, and it’s starting to get quite warm, and there’s nothing but the dark abyss of ever-denser hydrogen gas beneath you. You fall through this abyss for a very, very long time.

You eventually start to notice that the atmosphere has become thick enough that you can swim through it. It’s not quite liquid, not quite gas, but a “supercritical fluid” that shares properties of each. Your body would naturally stop falling and settle out somewhere at this level, where your density and the atmosphere’s density are equal. However, you’ve brought your “heavy boots” and continue your descent.

After a very, very long time of falling through ever greater pressure and heat, there’s no longer complete darkness. The atmosphere is now warm enough that it begins to glow - red-hot at first, then yellow-hot, and finally white-hot.

You’re now 30% of the way down, and have just hit the metallic region at 2 million atmospheres of pressure. Still glowing white-hot, hydrogen has become so dense as to become a liquid metal. It roils and convects, generating strong magnetic fields in the process.

Most materials passing through this deep, deep ocean of liquid metallic hydrogen would instantly dissolve, but thankfully you’ve brought your unobtainium spacesuit…which is good, because it’s now 10,000 C (18,000 F). Falling ever deeper through this hot glowing sea of liquid metal, you reflect that a mai tai would really hit the spot right about now.

After a very, very, very long time falling through this liquid metal ocean, you’re now 80% of the way down…when suddenly your boots hit a solid “surface”, insomuch as you can call it a surface. Beneath you is a core weighing in at 25 Earth-masses, made of rock and exotic ices that can only exist under the crushing pressure of 25 million atmospheres.

You check your cell phone to tell you friends about your voyage…but sadly, it melted in the metallic ocean - and besides, they only have 3G down here.

TL;DR: You would stop falling about 10% of the way down, where your density matches the density of the surrounding hydrogen “supercritical fluid”.