D-32: The Giant

The following was originally published on the Stellaris forums.

 

Good morning, everyone! Today we’re going to talk about a planet. A very large planet, in a very interesting system. Meet HD 114762 b; or as we call it unofficially, Latham’s Planet.

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This is the very first exoplanet that humans ever discovered. It was discovered in 1989 by a team led by Dr David Latham, hence the name, and was unconfirmed until 1991. This is incredibly early: Exoplanet searches didn’t really kick off in a serious way until the early 2000s. Latham’s Planet must have been a very special place to be noticeable in this way.

Oh, it is.

Latham’s Planet is enormous. Even now, with vastly more planets discovered, it sits solidly near the top of the table. We don’t know its exact mass but it’s between 11 and 63 times Jupiter. (If you think that’s an inexact number then you haven’t met enough astrophysicists.)

At the time when we discovered it, it gave us two shocks. The first is how close it is to its star, and the second is how eccentric its orbit is. In the Solar system all the gas giants are a long way out and all the orbits are neat and circular. Latham’s Planet was an early sign that this isn’t even close to universally true. At its furthest from the star it’s only one-third as far out as Earth is, and at its closest it’s one-tenth as far.

We think that anything which gets this close will quickly lose its atmosphere unless it’s very heavy and has a heavy atmosphere. Latham’s Planet, however, is nothing if not heavy, which once raised the question: is it actually a brown dwarf?

What’s a brown dwarf?

Gas giants are big balls of gas. Stars are balls of gas so big that they’ve begun to fuse the gases in their core. There isn’t a clear line between the two: some gas giants get large enough that they begin to undergo some limited fusion in their core, and thus straddle the line between stars and gas giants. They’re called brown dwarfs but a better image may simply be “like Jupiter but glowing slightly.”

In other words, Latham’s Planet may actually be Latham’s Really Small And Dim Star That’s Very Close To Another Star.

Is it a brown dwarf?

It turns out not. In 2014, Stephen Kane and Dawn Gelino applied more modern methods and showed that Latham’s Planet wasn’t glowing.

Can earthlike life exist there?

Not only no but hell no. Firstly it’s a gas giant much larger than Jupiter, its gravity would crush anyone. Secondly it’s incredibly close to its star: the light would be so intense that it would boil surface water. Thirdly and most importantly, it is a gas giant. You cannot live on a gas giant.

It might have moons, but since Latham’s Planet is not in the habitable zone, they would not be habitable by earthlike life either.

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So why do you mention this disappointing planet?

Because it’s important in human history: this is the first exoplanet we ever discovered. But also because I wanted to talk about gas giants. See, gas giants are pretty awesome.

Hydrogen will be a useful fuel in the future, especially if we go to space in a big way. We can use hydrogen to fuel fusion reactors and to create liquid water. Gas giants have rather a lot of it. In fact they have so much that below a certain point the gas wouldn’t actually be in gas form at all because the pressure would turn it liquid.

Many people have the image of spacecraft dipping down to the surface of a gas giant to skim off some gas for their engines. This is inaccurate for tworeasons. Firstly, there’s no clear “surface”, only a fuzzy region which fades between “atmosphere” and “void.” That region has too much gas in it to fly through easily but too little to be worth mining.

Secondly, descending to lower orbits and then ascending to lower ones is expensive in energy terms. This is especially true if the body you’re orbiting is heavy or you’re close to it. Latham’sPlanet is very heavy, and we’d need to be very close to skim the atmosphere. As a result doing this would almost certainly cost more energy than we got from it.

Unless we built a facility to do it.

If we were to put a station in low orbit aroundLatham’s Planet and dangle a space elevator down from it into the atmosphere, then we could mine all the gas we wanted and take it up to orbit for easypickup and delivery. It would even be in convenient pressurised form. This sounds easier than it is: the upper-atmosphere storms on Jupiter are scary places and there’s no reason to suppose thatLatham’s Planet will have it any easier. That space elevator is going to be blown around like tinsel in a hurricane.

It wouldn’t be a very desirable posting. We’d be better off leaving all the personnel – if there are any – in the orbital station and having the mining operation mechanised. However, if we needed fuel in space in that system then we would have as much as we wanted. To all intents and purposes we would never come even close to running out of gas from Latham’s Planet.

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