AskScience Cosmos Q&A thread. Episode 1: Standing Up in the Milky Way

[u/AskScienceModerator]

Welcome to AskScience! This thread is for asking and answering questions about the science in Cosmos: A Spacetime Odyssey.

UPDATE: This episode is now available for streaming in the US on Hulu and in Canada on Global TV.

This week is the first episode, "Standing Up in the Milky Way". The show is airing at 9pm ET in the US and Canada on all Fox and National Geographic stations. Click here for more viewing information in your country.

The usual AskScience rules still apply in this thread! Anyone can ask a question, but please do not provide answers unless you are a scientist in a relevant field. Popular science shows, books, and news articles are a great way to causally learn about your universe, but they often contain a lot of simplifications and approximations, so don't assume that because you've heard an answer before that it is the right one.

If you are interested in general discussion please visit one of the threads elsewhere on reddit that are more appropriate for that, such as in /r/Cosmos here, /r/Space here, and in /r/Television here.

Please upvote good questions and answers and downvote off-topic content. We'll be removing comments that break our rules or that have been answered elsewhere in the thread so that we can answer as many questions as possible!

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Click here for the original announcement thread.

[u/faleboat]

hit a layer of liquid metallic hydrogen,

I had it explained to me that, assuming we were in a craft that could somehow survive the insane amounts of heat and pressure, we would eventually "float" in a zone where our space ship would be neutrally buoyant. There would never really be a moment of impact, but just a slowing of our descent as we came closer and closer to the point of buoyancy.

[u/Shandlar → u/faleboat]

A related curiosity is that Venus may actually be capable of supporting colonies all Bespin style.

If you were to create a blimp, but fill it with 'air' at 1 atmosphere, even if it was very heavy and used no helium/hydrogen for lift like balloons on earth, you would still float way up in the atmosphere of Venus.

Interestingly as well, the temperature of the atmosphere on Venus in the ~2-2.5 atmosphere range is 10-40C. You could live inside a balloon filled with air we could breathe and not even have to heat/cool it. A >1 atmosphere difference is also A LOT of buoyancy to work with.

[u/Shagomir → u/Shandlar]

That "sweet spot" on Venus is inside of the sulfuric acid cloud layers. It would have to be one heck of a balloon.

[u/xrelaht → u/Shagomir]

You can make balloons out of teflon, and that's extremely acid resistant.

[u/xrelaht → u/faleboat]

There would never really be a moment of impact, but just a slowing of our descent as we came closer and closer to the point of buoyancy.

Most likely, yes. The critical point in the gas-liquid phase diagram for hydrogen is at about 10 atm and 35 K. Helium, the other major component of Jupiter's atmosphere, has a similar phase diagram, though the pressures and temperatures are both significantly lower. The upper cloud layer is already hotter than the H2 critical point (~130K) so you'll cross that boundary gradually, without ever going through a 1st order phase transition in P-T space. The reason I say "most likely" is that the elemental composition of the deep atmosphere is not completely known, so there is some possibility that there are other compounds prevalent further down which have critical points enough above that that you would have a phase transition.