Little Big Trouble

So throughout the Pre-Sequel, people and things are constantly reminding you about the lack of air on the moon. Janey even brings up the classic “Your eyeballs will pop like grapes when the pressure differential gets too harsh” bit. Now this phenomenon is known as explosive decompression, and it occurs when the pressure inside of a structure is much greater than the pressure outside and a rupture opens in the structure’s surface. The structure then begins to tear open as the air inside attempts to escape, and depending on how harsh the pressure differential is, it could potentially explode.

Now, we do observe explosive decompression occurring in the game, most notably in the beginning of the game when the shipping container you land in opens for the first time. However, the force of this decompression isn’t too terribly strong, which suggests that there was some sort of outside pressure that it could attempt to equalize with. After all, explosive decompression can happen without a vacuum. A balloon popping is the same principle at work.

Furthermore, if there were no atmospheric pressure at all, what Janey said would have been absolutely correct. The Vault Hunters’ eyes would’ve popped out of their heads by the time they reached the first O2 generator. But they all seem to be totally fine in this presumed vacuum, and can even last for several minutes without any protective gear. Not to mention, the effects on their health are rather slow, and simply standing over an O2 leak can fix it despite a tiny vent like that not providing any pressure at all.

So it’s safe to assume that there is in fact an atmospheric pressure from the way our heroes don’t explode upon entering it. But I can hear some of you saying, “But op, that’s just because it’s a video game. They don’t want you to die immediately just by not having an Oz kit,” which may be correct. But there’s actually more evidence to show that an atmosphere exists. And that evidence is that there are flying enemies on Elpis.

Now I don’t mean the stupid Dahl Jetfighters or dudes with jetpacks, but the actual fauna of Elpis. The Rathyds and Shugguraths.

Rathyds are somewhat bat-like, and Shugguraths are big bulbous things that just seem to levitate. Both of these animals require an atmosphere in order to fly. The Rathyds are a bit easier to explain, and it’s simply because wings require air to function. They need something to push off of to stay airborne. Shugguraths are a bit more complicated, and a little less obvious, and in order to come to a reasonable conclusion with the information we’re given, we have to do a little guesswork. From my best assumption, Shugguraths are able to float due to some kind of organ similar to a fish’s air bladder. Fish (or at least certain kinds) have a dedicated organ to control buoyancy in water. Filling it up with air will make them lighter than the water and cause them to rise, while emptying it will make them heavier and cause them to sink. Based on the Shuggurath’s size and appearance, most of it’s body may serve this function, filtering in large amounts of light air particles to float higher, and expelling those particles to settle down. This also assumes it has a method of filtering those lighter particles, but the human body can tell the difference between oxygen and carbon dioxide, so it stands to reason that it can.

So, we have definitive proof that there is some sort of atmospheric pressure on Elpis, but how much, and what is it made of?

The “how much” question can be answered pretty simply actually. Elpis has a much smaller gravitational pull than say, Pandora, so it wouldn’t be able to retain enough air particles to create a “normal” pressure level that humans would be able to tolerate, at least immediately. In terms of the effects, it’s similar to how the air thins as you climb to higher altitudes on Earth. It takes some getting used to, but humans can absolutely live comfortably there. It’s more than likely a bit more harsh on Elpis, since it’s a much smaller mass, which would also explain why most Scavs, soldiers, and explorers opt to wear spacesuits. It just makes the excursions more comfortable. Furthermore, even though there are flammable compounds in the atmosphere (which I’ll get to soon), this limited pressure would prevent combustion as well. There simply just aren’t enough molecules in a close enough proximity for a flame to grow, and that’s why you can’t ignite enemies outside a building.

As for the atmosphere’s contents, there are two main compounds we can surmise make up most of the atmosphere: oxygen and methane. Elpis is shown to be rather cold pretty much all the time. There are caves of frozen methane just beneath the moon’s surface. However, Pandora is located in a solar system with two suns, and has a day/night cycle of around 90 hours. Judging by this, Elpis, with it’s apparent lack of an ozone layer, likely has extremely harsh temperatures akin to a desert. Blistering heat during the day, frigid cold at night. And since there’s nothing to lock that heat from the day in, chances are it wouldn’t penetrate very deep. But that methane does sometimes melt and make it’s way to the surface, and when it does, the heat of the day is going to evaporate it and send it into the atmosphere.

Aditionally, Elpis houses pockets of oxygen, which is made apparent by the vents that you can stand in to refill your Oz kit. These vents are fairly numerous in the locations you visit, but they aren’t particularly large, and we can’t say for certain whether or not the same goes for the entirety of the moon. In any event, this oxygen leaking from the moon’s surface would still be held in by the moon’s gravity, even in small amounts. This would certainly contribute ever so slightly to the atmosphere of Elpis.

But there’s actually one more compound that can also be thrown into the mix: ethane. It’s mentioned by Nurse Nina during the quest, “A Bunch Of Ice Holes,” that Elpis’ caves are stores of frozen “methane, ethane, and other ane”. While we can’t determine exactly what this “other ane” is, ethane most certainly is a real element, and it would have to exist in somewhat similar quantities to the methane in order to be of note. Though there’s likely more methane on the planet, and subsequently in the atmosphere as well.

So to tie everything together, we have an atmosphere of methane, ethane, and trace amounts of oxygen. The harsh day temperatures on Elpis evaporate the liquid methane and ethane into the air, while pockets of oxygen leak from vents on the surface. The low gravity of Elpis isn’t able to keep a high enough pressure for humans to comfortably inhabit, which leads to explosive decompression for the various pressurized containers scattered about. This atmosphere is to thin, and has too little oxygen for humans to breathe without specialized equipment, or for fires to burn, but is still dense enough for the fauna to achieve flight (and as a bonus, ethane as a compound has nearly twice the molecular weight as both oxygen and methane, which come out about the same, so a Shuggurath could absolutely use the oxygen and methane to stay buoyant in an ethane rich atmosphere).