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I have this Earth-like planet that is running short on materials, like minerals and gasses, and they have a big spaceship that is able to gather materials from a gas giant that orbits the same star the planet does. What materials might the planet need that a gas giant could be realistically made of?

I am no expert, thus I'm asking, but I know that for an atmosphere to be breathable you need at least Nitrogen and Oxygen and that the gas giants in the Solar System are mainly made of Hydrogen (please correct me if i'm wrong). Now, it doesn't necessarily need to be a gas giant, but it must be at least a planet made of something the main planet is needing, like solid nitrogen that once melted gets pumped into the atmosphere, but is that even possible? What materials might a planet in a super distant future need for its own survival?

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    $\begingroup$ I suggest reconsidering accepting my answer. Generally in SE is advised to wait at least 24 hours before accepting an answer. You are more likely to get more ideas and they may be more fitting. Besides @notovny said basically the same thing (focusing on the isotope Helium 3, mine was more generic) 2 minutes before I posted :) $\endgroup$ – Duncan Drake Sep 10 '20 at 14:55
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    $\begingroup$ You do not need nitrogen to breathe. $\endgroup$ – Edgar Bonet Sep 11 '20 at 12:32
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Helium-3.

Helium 3, or Trialphium, is the lighter, rarer stable isotope of helium that is often suggested as a fuel source for advanced fusion plants, because Deuterium-Trialphium fusion is aneutronic, so the reactor housing doesn't need to deal with neutron irradiation the way that the lower-temperature Deuterium-Tritium fusion does, and the charged particles produced by D-3He fusion are easier to convert directly to electrical power.

As a light, non-reactive gas, Helium-3 is generally rarer on Earth than in other parts of the solar system, -- monatomic helium tends to escape from the atmosphere of Earth over geologic timescales, and unlike Helium-4, which can be replenished from radioactive decay, Earth's Helium-3 is primordial, and potential replenishment from the Solar Wind is typically stopped by the Earth's atmosphere and magnetosphere. As a result the fraction of available Helium that's 3He is lower on Earth than in other solar system bodies.

In a high-tech, long-lived civilization, it may initially be feasible to obtain Solar-wind-deposited-Helium-3 from strip-mining the surface of their moons, but ultimately, if they have a light nearby gas giant like a Saturn or so, and decent in-system spacefaring technology, obtaining it from the upper atmosphere may be more economical.

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  • $\begingroup$ But we have no idea whether the civilization in question has any particular use for helium-3. Helium in general, yes, lots of uses for that. $\endgroup$ – jamesqf Sep 10 '20 at 17:58
  • $\begingroup$ @jamesqf well, the Nazis wanted it. We must get it too. $\endgroup$ – Duncan Drake Sep 10 '20 at 19:39
  • $\begingroup$ @jamsesqf As mentioned in the Wikipedia article ,D-3He is believed to be good for high-temperature fusion without having to deal with the neutron irradiation of the reactor housing you get with D-T fusion, which could make for lighter reactors.. Admittedly, without more details on the available technology, it's difficult to suppose whether the civilization in question needs to go that route. $\endgroup$ – notovny Sep 10 '20 at 19:47
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    $\begingroup$ Does radioactive decay replenish Helium-4 quickly enough to fill everyone's party balloons? $\endgroup$ – Michael Hampton Sep 11 '20 at 4:20
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    $\begingroup$ @RossPresser Yeah, you're probably right if they have moons available that they haven't already strip-mined for 3He. I guess it's possible that a sufficiently old civilization has done so, and the sci-fi setting I was thinking of when suggesting the answer was written 20 years ago and may have underestimated Lunar 3He supplies. $\endgroup$ – notovny Sep 11 '20 at 16:00
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Helium

Helium has an influx from the Earth crust into the athmosphere. From there it eventually escapes into space. See Can helium disappear from Earth?

In the case of your planet that has already happened. Either their crust emitted less helium or more escaped anyway they ran out of it.

Some people may think it is important just for baloons and talking funny at parties but it is actually very useful: 15 uses for helium you never knew existed

But here are good news! There is Helium on Jupiter! Actually it rains
Helium rain on Jupiter

So, provided that the big spaceship manages to avoid falling in the gravity pit, you can go there and lower the bucket.

P.S. notovny was 2 mins faster :)

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Helium-3 is the most economical choice for mining from a gas giant. Hydrogen, ammonia, and methane are very easily produced, and nitrogen is in abundance and not going anywhere.

But if your Earth-like planet has an Earth-like moon, then there's a good chance Helium-3 is there too. Should probably look there before sucking dry a gas giant.

Now, it doesn't necessarily need to be a gas giant, but it must be at least a planet made of something the main planet is needing

In our own solar system, we've got proposals to profitably mine at least 11 different bodies, we're thinking of mining bodies made of magnesium silicate, aluminium, iron silicate, nickel, iron, cobalt, gold, platinum and... water.

(Water is converted to fuel for the return trip - saving lifting it off the planet)

You also can mine (more like dismantle) Mercury for free energy.

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Helium is not only important for Fusion. Hightec often needs a cooling to 3 or less Kelvin. Thats mosttime done with Helium 4. (The normal one). The Large hadron colider in CERN institiute for examle, needs a couple of % of the worldwide traidable helium. Helium will become more and more expensive in our future. The most helium comes from the Oil and Gas industrie, but when this industire stopps, it will become very expensive.

Gasgiants are made of hydrogen to almost 90% and almost 10% Hydrogen. All other stuff together has less than 2%.

Nitrogen is a good idea too. You will need it for Terraforming, or Big Spacehabitats. Even if a Gasgiant has only 0,1% in his Atmosphere it would be a good source.

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